[Rob Thompson] Manufacturing Processes for Design

September 13, 2017 | Author: ashade | Category: Welding, Production And Manufacturing, Industrial Processes, Industries, Plastic
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Manufacturing Processes for Design...

Description

Manufacturing Processes for

Design Professionals

¦;*>

Hob Thompson

Manufacturing Processes for

Design Professionals

Contents On the previous spread: The Eye chair, designed by

How to use this book 8

Introduction 10

Jackie Choi for Boss Design (see pages 342-343).

The importance of materials and manufacturing knowledge for successful design practice

Any copy of this book issued by the publisher as a paperback is sold subject to the condition that it shall not by way of trade or otherwise be lent, resold,

hired out or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published and

Part One

Forming Technology

without a similar condition including these words being imposed on a subsequent purchaser.

Plastics and Rubber First published in the United Kingdom in 2007 by Thames & Hudson Ltd,i8iA High Holborn, London wcivyox

Blow Molding

Tube and Section Bending

22

Extrusion Blow Molding (EBM)

Thermoforming

© 2007 Rob Thompson

Reprinted 2010

All Rights Reserved. No part of this publication may

Forging

Plug-assisted Forming

Drop Forging

Twin Sheet Thermoforming

Roll Forging

Vacuum Casting

36 40

Compression Molding

Ul*

Compression Molding Rubber

any means, electronic or mechanical, including

Compression Molding Plastic

Injection Molding

Sand Casting Die Casting

50

Metal Injection Molding

Moldflow analysis

Electroforming

permission in writing from the publisher.

Gas-assisted Injection Molding

Centrifugal Casting

Multishot Injection Molding

Press Braking

Reaction Injection Molding

the British Library

Dip Molding

Designed by Christopher Perkins Printed and bound in China

72

Dishing

Open Bending

120 124

Glassblowing

Wet Lay-up

130 136 140 144 148

Rapid Prototyping 232

Backpressure Forming Diaphragm Forming

Stereolithography (SLA)

160

Mandrel Forming

Clay Throwing Ceramic Slip Casting

88 92

Press Molding Ceramics Jiggering Ram Pressing

Selective Laser Sintering (SLS) Direct Metal Laser Sintering (DMLS)

Bending

78 82

Secondary Pressing

Bubble Forming

3D Rotary Laminating (3Drl

152

Machine Press and Blow

Lampworking

Planishing

Cavity Forming

Filament Winding 222 3D Thermal Laminating 228

Layered Manufacturing

Hole Boring

Deep Drawing

Resin Transfer Molding

DMC and SMC Molding 218

Machine Blow and Blow

Wheel Forming

Superforming

Pre-preg Lay-up

Studio Glassblowing

Blowing

Metal Stamping

Composites Composite Laminating 206

Glass and Ceramics

Jig Chasing

Metal Spinning

Circle Bending

3D Laminating I3DL)

64 68

Metal Panel Beating

Steam Bending 198

Paper Pulp Molding 202

In-Mold Decoration

A catalogue record for this book is available from

ISBN 978-0-500-51375-0

m

Low Pressure Die Casting

storage and retrieval system, without prior

British Library Cataloguing-in-Publication Data

Veneer Lamination

110

High Pressure Die Casting

Investment Casting

Kerfing Solid Wood Lamination

Hydraulic Swaging

Pressure Forming

be reproduced or transmitted in any form or by

photocopy, recording or any other information

30

Roll Forming

Rotation Molding

104

Rotary Swaging

Vacuum Forming

Wood CNC Machining 182 Wood Laminating 190

Ring Rolling

Swaging

Injection Blow Molding lIBM) Injection Stretch Blow Molding (ISBM)

www.thamesandhudson.com

98

Mandrel Bending

168 172 176

/•

Part Two

Part Four

Cutting Technology

Finishing Technology

Chemical Photochemical Machining

Mechanical

Additive Processes

Subtractive Processes

Printing

2UU Punching and Blanking 260

Spray Painting 350

Grinding, Sanding and Polishing 376

Screen Printing 400

Die Cutting 266

Powder Coating 356

Thermal

Wheel Cutting

Pad Printing 404

Laser Cutting

248 Water Jet Cutting 272

Electrostatic Spraying

Belt Sanding

Hydro Transfer Printing 408

Electrical Discharge Machining

254 Glass Scoring 276

Fluidized Bed Powder Coating

Honing

Foil Blocking and Embossing 412

Die Sink EDM

Anodizing 360

Wire EDM

Electroplating 364

Electropolishing 384

Galvanizing 368

Abrasive Blasting 388

Vacuum Metalizing 372

Lapping

Photo Etching 392 CNC Engraving 396

Part Three

Part Five

Joining Technology

Materials

Thermal Arc Welding

Soldering and Brazing 312

Introduction to Materials 418

Wood and natural fibres

282 Conduction Method

Manual Metal Arc Welding (MMA)

Torch Method

Plastics

introduction to Wood 464

Metal Inert Gas Welding IMIG)

Furnace Method

Introduction to Plastics 424

Softwoods 470

Staking 316

Thermoplastic 430

Hardwoods 472

Plasma Welding

Hot Air Staking

Thermoset 440

Natural fibres 480

Submerged Arc Welding (SAW)

Ultrasonic Staking

Bioplastic 446

Tungsten Inert Gas Welding (TIG)

Power Beam Welding Laser Beam Welding [LBW]

Mechanical

Electron Beam Welding (EBW)

Friction Welding

294 Joinery 324

Rotary Friction Welding (RFW)

Weaving 332

Linear Friction Welding (LFW)

Upholstery 338

Orbital Friction Welding (OFW)

Timber Frame Structures 344

Friction Stir Welding (FSWl

Vibration Welding Ultrasonic Welding Resistance Welding Projection Welding

Ceramics and Glass

288 Hot Plate Welding 320

Metals

Introduction to Ceramics and Glass 482

Introduction to Metals 448

Ceramics

Ferrous

Glass

454

488

490

Non-Ferrous 457

Directory Glossary and Abbreviations 496

298 302 308

Featured Companies 502 Organizations and Other Sources 512

of Information Further Reading 516

Spot Welding

Illustration Credits 519

Seam Welding

Acknowledgments 522 Index

524

Manufacturing Processes for Design Professionals

How to use this book Manufacturing Processes for Design Professionals explores established, emerging and cutting-edge production techniques that have, or will have, an important impact on the design industry. There is a danger today of designers becoming detached from manufacturing as a result of CAD, globalization and design education. This book aims to restore the balance with

Forming Functions

a hands-on and inspiring approach to design and production. It is a comprehensive, accessible and practical resource that focuses on providing relevant information to aid fast and efficient

Bend

Continuous

Sheet

Internal

decision-making in design projects. Cutting Functions

STRUCTURE

the process through 3 key elements.

HOWTO USE THE CASE STUDIES

This book is organized into 2 main

The text gives an analysis of the typical

The Processes section features real-life

sections: Processes and Materials.These

applications, competing or related

case studies from factories around

can be used separately or in combination.

processes, quality and cost, design

the world.The processes are explained

Each section contains design guidance

opportunities and considerations, and

with photographs and analytical and

supplied by manufacturers to ease

environmental impacts of a process.

descriptive text. All types of production

the transition between design and

There is also a full technical description

are included, from one-off to batch and

production and provides information

of the process and how the machinery

mass. For cross-comparison the case

that will inspire decision-making,

involved works, with diagrams, and a case

studies can be set against each other on

encourage experimentation and support

study showing products or components

many levels, including functions, cost,

pollination of ideas between industry

design ideas.

being made by a leading manufacturer

typical applications, suitability, quality,

and design.This ensures that designers

using the featured process.

competing processes and speed.This

fully utilize the potential of their

information is accessible, logical and at

industrial toolbox to create forward-

External

Internal

Channel

Surface

Joining Functions

Overlap

HOWTO USE PROCESSES

On the opening spread of each

The Processes section is organized into

process you will find a data panel, which

4 parts, each focusing on a specific

provides a bullet-pointed summary of

type of technology, and each process is

factors such as the typical applications,

HOWTO USE MATERIALS

explained with photographs, diagrams

quality and cost, as well as function

Each manufacturing process can be used

and analytical and descriptive text.The 4

diagrams (see opposite) which, when highlighted, indicate the particular

to shape,fabricate andfinish anumber

are: Forming Technology (blue), Cutting Technology (red), Joining Technology (orange) and Finishing Technology

functions and design outcomes of each

of the material profiles is to support

process. These function diagrams quickly

the processes, expand opportunities

enable the reader to compare a wide

for designers and provide relevant

(yellow). Each featured manufacturing

range of similar processes to see which is

information for potential applications.

process is fully illustrated and provides

the most effective in producing a given

The layout of the Processes and Materials

a comprehensive understanding of

item or component.

sections is designed to encourage cross-

parts (colour coded for ease of reference)

the forefront of each process.

Finishing Functions

thinking and engaging products for the future.

of different materials.The main objective

Preparation Colour Appearai

Protection Information

HOW TO USE THE FUNCTION ICONS

materials are more suitable for certain

These Icons represent the function that

functions than others. These Icons guide

each process performs. The functions are

designers In the early stage of product

different for forming, cutting, joining and

development by highlighting the relevant

finishing processes. Likewise, different

processes and materials for their project.

vlanufactui ing Processes for Design Professionals

Introduction Manufacturing technology is both fascinating and inspiring. The products around us are the result of the delicate touch of craftsmen, highly mechanized production, or both. The Processes section gives first-hand insight into a range of manufacturing techniques including mass producing everyday products, batch producing furniture and prototyping with some of the most advanced

Manufacturing is continually in a state of transition.The level of technology is different in various industries, so whilst some manufacturers are leading the way, such as in the production of

carbon fibre composites (page 214) and rapid prototyped plastics and metals (page 232), others are maintaining

highly skilled traditional crafts. The

technologies we have at our disposal. The visual case studies,

combination of craft and industrial

combined with in-depth technical analysis, show what happens now

techniques in processes such as panel

and how designers and research institutes are continually pushing

beating metal (page72),jiggering and jolleying ceramics (page 176) and steam

the boundaries of what will be possible in the future.

bending wood (page 198) produces

Bellini Chair

Panasonic P901iS smartphone

Designer/client: Mario Bellini/Heller Inc. Date: 1998 Material: Polypropylene and glass fibre

Designer: Panasonic. Japan

Manufacture: Injection molded

Date: 2005 Manufacture: Injection molded plastic covers using Yoshida Technoworks in-mold decoration technology

articles that unite the user and maker with a sense of pride and ownership.

The examples in this book demonstratethe inner worldngs

50) is now one of the most important

(page 50). It is also possible to integrate

of a 1 arg e ran g e of m anufacturin g

processes for designers, and probably

fabric, metal foils and leather (see image,

processes. In some cases the tasks are

the most widely used. It is utilized to

above right) into plastic moldings. Gas

carried out by hand to demonstrate the

sh ape th erm opl asti cs an d th erm os etti n g

assist injection molding produces hollow,

techniques more clearly.The continued

plastics, waxes for investment casting

rigid and lightweight plastic parts (see

importance of an operator is evident in

(page 130) and even metals (page 136). It is continually developing and in

image, above left).The introduction of

many processes. Even mass-production techniques, such as die cutting and

recent years has been revolutionized by

the amount of pressure required in the

assembling packaging (page 266),rely

in-mold decoration (page 50) and gas

molding cycle. Surface finish is improved

on an operator to set up and fine tune

assist technologies (page 50). In-mold

because the gas applies internal pressure

the production line. But, where possible,

decoration is the application of graphics

while the moldis closed.

manual labour is being replaced by

during the molding process, eliminating

computer-guided robotic systems.The

finishing operations such as printing.

within injection molding is multishot.

aim is to reduce imperfections caused

With this technology it is possible to

This is the process of injecting more

by human error and minimize labour

apply graphics on 1 side, both sides or

than 1 plastic into the same die cavity to

costs. Even so, many metal, glass, wood

onto multishot injection molded parts

produce parts made up of materials with

and ceramic processes are based on manufacturing principles that have changed very little over the years.

DEVELOPMENTS IN FORMING Plastic products have come a long way since they were first formed by

compression molding (page 44) in the 1920s. Injection molding (page

gas reduces material consumption and

Another area of important progress

^3

o a c: o ;H o z

widely used to describe the matt texture produced by EDM. Nowadays, mobile phones and similar products are more often produced with in-mold decoration, which requires a gloss finish. Whereas mass production is limited

by high tooling costs and thus high volume production of identical parts, each product directly manufactured

from CAD data is limited only by the imagination and capabilities of the designer. Rapid prototyping (page 232) is one of these processes: it is not yet suitable for mass production, but it is capable of producing similar volume parts whose shape is different each time without significant cost implications.

Combined with the possibility of making shapes not possible with any other process, these techniques are giving rise to a new design language. For example, one-off and 1 ow volume products have emerged in recent years that are designed by the customers and merely

facilitated by the designer. Also, the US military are using rapid prototyping to Entropia

different colours,hardnesses,textures or

make spare parts for their equipment, as

Designer/client: Lionel Dean, FutureFactories/

transparency. Over-molding is a similar

opposed to waiting for delivery.

Kundalini Date: 2006 Material: Polyamide (PA) nylon Manufacture: Selective laser sintering (SLS1

process; the difference is that over-

Recently metal powders have been

molding is not carried out in the same

added to the list of materials that can be

tool. Using this technique, materials other than plastic can be integrated into

shaped by rapid prototyping. At present, rapid prototyping metal is best suited

injection molding.

to the production of parts no larger

Developments in plastic molding

than about 0.01 m3 (0.35 ft3). Even so, the

are also affected by improvements in

opportunities of this process are vast,

metalworking technologies.The surface

because larger parts can be made by

finish on mobile phones and other

investment casting (page 130) a rapid

small consumer electronic equipment

prototyped wax or plastic pattern.

became almost standardized due to the development of electrical discharge

Thermoforming (page 30) is a process generally associated with plastic

machining (EDM) for plastic mold

packaging. However,Superform

making.This process makes it possible to

Aluminium in the USA and UK have

machine concave profiles (molds) to the same high degree of precision as relief profiles. High voltage sparks between

a copper electrode (tool) and metal workpiece vaporize surface material. The rate of spark erosion determines the surface finish and so it is used to simultaneously cut and finish metal parts. Hence the term 'sparked' finish was

Roses on the Vine Designer/client: Studio Job/Swarovski Crystal Palace Project Date: 2005 Material: Aluminium base with red and peridot coloured Swarovski® crystal Manufacture: Base laser cut and gold anodized

Laser Vent polo shirt

Outrageous painted guitar

Designer: Vexed Generation

Date: Spring/Summer 2004 Material: Quick dry polyester microfibre

Paint by: Cambridgeshire Coatings Ltd/US US Chemicals and Plastics Date: 2003

Manufacture: Laser cutting and stitching

Material: Illusion Outrageous paint Manufacture: Spray painting

Biomega MN01 bike

Camouflage printed rifle stock

Designer: Marc Newson

Designer:

Date: 2000

Material:

Material: Aluminium alloy frame

Manufacture:

Hydrographies Plastic stock Hydro transfer printing

Manufacture: Superforming and welding

Notes:

The transfer films can be decorated with artwork, photographs or patterns.

developed a range of processes, known as

materials. Indeed, laser cutting is used

cut edge is sealed by the heat of the

superforming (page 92), that are capable

a great deal by architects for model

laser, eliminating conventional hems

of shaping aluminium alloys (page 457)

making within short timeframes.

and magnesium alloys (page 458) using

Roses on the Vine by Studio Job (see

and reducing material usage. Another

benefit of specifying laser cutting was

a similar technique. At around 4500C

image, page 13), is an example of how

that vents could be integrated into areas

(8400F) certain grades of these metals

laser cutting can be used to produce

that needed better ventilation or greater

become superplastic and so can be

intricate, complex and otherwise

freedom of movement.

stretched to many times their length

impractical shapes with very high

without breaking. Since the development

precision.This cutting process is not

DEVELOPMENTS IN JOINING

of commercially viable metals and

limited to rigid materials. In 2004 Vexed

Powerbeam technologies (page 288),

processes in the mid 1970s, superforming

Generation launched Laser Vent. The

which include laser beam and electron

has had a major impact in the

aim of the designers was to create ultra

beam, are making an impact in joining

automotive, aerospace and rail

lightweight clothing for cyclists, but with

as well as cutting applications. Electron

industries. Recently, designers such as

the aesthetic of low-key leisurewear and

beam welding is capable of producing

Marc Newson have begun to explore the

so suitable for the office.They achieved

coalesced joints in steels up to 150 mm

possibilities of using this technology to

this by laser cutting synthetic fibre. The

(5.9 in) thick and aluminium up to

produce consumer products such as bicycles (see image,opposite).

DEVELOPMENTS IN CUTTING Like rapid prototyping, laser cutting (page 248) works directly from CAD data. This means that data can be translated very readily from a designer's computer onto th e surface of a wi de ran g e of

I

450 mm (17,7 in) thick. Laser welding is not usually applied to thick materials,

interiors, mobile phones, packaging and

cannot always be produced with lower

camouflaging gun stocks (see image,

volumes ones. For example, blow

but a recent development known as

page 15 above right).

molding plastic (page 22) and machine glassblowing (page 152) are limited

weld clear plastics and textiles (page 288).This technique has the potential to

SELECTING A PROCESS

to continuous production due to the

Process and material selection is integral

nature of the process. Therefore, there

transform applications that are currently

to the design of a product. Economically,

is very little room for experimentation.

limited to coloured materials.

it is about striking a balance between the

In contrast, the qualities of injection

Joinery (page 324) and timber frame construction (page 344) have changed

investment costs (research, development

molding can be reproduced with

and tooling) and running costs (labour

very little over the years. Developments

vacuum casting (page 40) and reaction injection molding (page 64), for instance.

have mostly been concentrated in

and materials). The role of the designer is to ensure that the available technology

This means that low volumes can be

materials such as new types of

will deliver the expected level of quality.

produced with much lower initial

Clearweld® makes it possible to laser

engineering timbers (page 465) and

High investment costs are usually

costs and therefore a higher level of

biocomposites. However, in 2005 TWI

only justifiable for high volume products,

experimentation is usually possible.

assessed the possibility of joining wood with techniques similar to friction

whereas low volume products are limited

Process selection will affect the

by high labour and material costs.

quality of the finish part and therefore

welding metals (page 294) and plastics (page 298). Beech and oak were successfully joined by linear friction

Therefore, the tipping point comes when

the perceived value. This is especially

expected volumes outweigh the initial

important when 2 processes can produce

costs.This can happen before a product

the same geometry of part. For example,

welding (see image, page 295). Friction welding revolutionizedmetalwork by eliminating the need for mechanical

has reached the market, or after years of

sand casting (page 120) and investment

manufacturing at relatively low volumes.

casting (page 130) can both be used to

The cost of materials tends to have a

manufacture 3D bulk shapes in steel.

fasteners, and in the future the same

greater impact in high volume processes.

However, due to the lower levels of

could happen in woodwork.

This is because labour costs are generally

turbulence, investment casting will

reduced through automation.Therefore,

produce parts with less porosity. It is

DEVELOPMENTS IN FINISHING

fluctuations in material value caused by

forthis reason that aerospace and

There have been many developments in

rising fuel prices and increased demand

automotive parts are investment cast.

finishing, but spray painting remains one

affect the cost of mass produced items.

of the most widely used processes, from

Occasionally the cost of production is

33

o o

c o H o

DESIGN SOFTWARE

irrelevant, such as composite laminating

Predicting and testing the quality of

years arange of sprayed finishes have

carbon fibre racing cars (page 214). Until

the finished part has become more

evolved including high gloss, soft touch,

recently, this has been too expensive

reliable with developments in computer

thermochromatic, pearlescent and

for application in commodity products,

simulation software, such as finite

to maximize the efficiency of the

iridescent. The cost of paint varies

but due to recent developments in

element analysis (FEA).There are

operation (see images, above); previously,

FEA is used to predict accurately how the

dramatically depending on the type and can be very high for specialist paints such

the production techniques it is now

many different programmes, which

tools were engineered and then tested

part will perform in application (pages

becoming more common in sports

are becoming more widely used in the

and adjusted accordingly. FEA software

124-9,214 and 226-7).This does not

as the Outrageous range (see image,

equipment and automotive parts.This is

process of design for manufacture

is not used in all forming applications,

de-skill the process of engineering;

pageij above left). A film of aluminium is incorporated into spray painted finishes

(pages 50-63,64-7 and 130-5), and

but it does have many advantages.

it is another tool that can help to

it is no longer limited to high volume

Most importantly, it reduces tooling

minimize material consumption and

by vacuum metalizing (page 372) to give

also partly due to the obvious benefits of improved strength to weight. The design features that can be

production. The forming of many

costs, because parts can be molded

double-check calculations made by

the appearance of chrome, silver or

achieved with high volume processes

products is simulated using FEA software

'right first time'.

designers and engineers.

one-off to mass production. Over the

an 0di zin g, or for functi on al purposes, such as heat reflection.

Hydro transfer printing (page 408) has recently transformed spray painting.

With this process it is possible to wrap printed graphics around 3D shapes.This

means anything that can be digitally printed can be applied to almost any surface. Applications include car

As well as mold flow simulation,

FEA simulation of an aluminium forging Software: Professional Engineer (Pro E) and

Forge3 SimuLatlon by: Bruce Burden, W.H. Tildesley Ltd

Material: Aluminium alloy Manufacture: Forging

Case Study

^ Binding this book I ~ This bool< demonstrates the techniques used

cut to size on a guillotine. Therefore, the

to manufacture many of the products that

extent of books bound in this way is divisible

surround us in our day-to-day lives. Like most

by the number of pages in a section, which

commercial books, it is manufactured using

is typically 4,8 or 16. Perfect binding is not

a process similar to traditional bookbinding.

limited by the same factors and so can be

And whether hardcover or paperback, it is

any number of pages.

made of folded sections stitched together

Linen tape is adhesive bonded onto

in a process known as section-sewn binding

the sewn edges of the sections and

(image i). An alternative method is perfect

the sewn assembly is cut to size in a

binding, which is the process of adhesive

guillotine (image 3). This produces a neat

bonding Individual pages into a scored paper

edge (image 4). Hard covers are made up

cover. It is less durable and so is limited to

of heavy-duty grey board 2.5 mm (0.1 in.)

thinner books, but the advantage is that the

thick concealed in paper, cloth or leather.

pages can be opened out flatter than section-

By contrast, paperback covers are heavy-

sewn bindings.

duty paper, which is typically around

This sequence of images demonstrates section-sewn case binding on a smaller book

0.25 mm (0.01 in.) thick. Any printed

decoration, such as hot foiling (pages 412-

than this, but the principles are the same.

5) is applied prior to assembly. The cover

In this case, the sections are made up of i5

Is adhesive bonded to the first and last

pages (image 2), which consist of a large

page, the assembly is clamped in a press

signature (printed sheet) folded 4 times and

and the adhesive cures (image 5).

Featured Company

R S Bookbinders www.rsbookbinders.co.uk

Forming Technology

Extrusion Blow Molding Process Polymer granules Conventional extrusion screw and barrel assembly

fj11

Forming Technology

{=^

Blow Molding

Part sealed

1 Extrusion die

Blow pin removed

. Extrused parison Split mold

ft

Molds open

Flash removed with profiled cutter

w

This group of processes is typically used to mass produce hollow packaging containers. They are a very rapid production method

O

for large volumes of thin walled parts.

Finished part

A

u 1 Moderate tooling costs 1 Low unit costs

Quality • High quality, uniform thin walled parts • High quality surface finish that can be gloss, textured or matt

Typical Applications

Suitability

• Chemical packaging • Consumer packaging • Medical packaging

• Suitable only for high volume production runs

Related Processes

Speed

• Injection molding • Rotation molding • Thermoforming

Stage 2: Blowing

Stage 3: Demolding

Stage A: Trimming

In stage 1 of the EBM process, a conventional

once the parison has reached a sufficient

parison to take the shape of the mold. The

extrusion assembly feeds plastlcized

length the 2 sides of the mold close around

hot polymer solidifies as It makes contact

polymer into the die. The polymer is forced

It. A seal Is formed along the bottom edge.

with the cold tool. In stage 3, when the part

over the mandrel and emerges as a circular

The parison Is cut at the top by a knife and

Is sufficiently cool the mold opens and the

tube, known as an extrused parison. The

moved sideways to the second station, where

part Is ejected. In stage U, the container Is

extrusion process Is continuous. In stage 2,

air Is blown In through a blow pin, forcing the

deflashed using a trimmer.

RELATED PROCESSES

that a wider range of anti-tamper and

pints). EBM can create the largest variety

among other materials.Typical materials

Thermoforming (page 30),rotation molding (page 36) and injection molding (page 50) can all be used to form the

other caps can be introduced.

of containers ranging between 3 ml

for the ISBM process include PE and PET

a wide choice of materials can be used in

molding is a complex process with which

COSTS

care applications.

same geometry parts. Even so, blow

this process, and complex and intricate

to work. Expert advice from engineers

Tooling costs are moderate. EBM is the

shapes manufactured.

and toolmakers is required to guide the

least expensive, the tooling for I BM is

TYPICAL APPLICATIONS

molding is the process of choice for large volumes of hollowthin walled packaging.

design process through to completion.

typically twice as much and ISBM is the most expensive.

• Very rapid cycle time (typically 1-2 minutes)

INTRODUCTION

very accurate neck finishes and the

Blow molding is carried out In 3 different

stretch cycle gives superior mechanical

ways: extrusion blow molding (EBM), injection blow molding (IBM) and injection stretch blow molding (ISBM).

properties. ISBM is particularly suitable for beverage, agrochemical and personal

Each of the processes has its particular

design opportunities and is suitable for

Stage 1: Extruded parison

TECHNICAL DESCRIPTION

The main advantages of EBM are that

ISBM can be used to produce clear

and 220 litres (0.005-387 pints). Blow

containers with very high clarity.

There are many considerations that need

chemical,veterinary and consumer

QUALITY

Stretching the pre-form during blowing

to be taken into account when designing

applications because it has low tooling

industries to produce intravenous

The surface finish is very high for all

greatly increases the mechanical

for blow molding, including the user

may contain ic or more cavities and eject

and running costs. It is a versatile process

containers, medicine bottles and vials,

of these processes.The IBM and ISBM

and con sum er packaging.

technologies have the additional

strength of the container by aligning the polymer chains longitudinally.These

(ergonomics), product (light sensitivity of contents andviscosity), filling (neck,

a batch of parts every 1-2 minutes.

that can be used to produce a wide

advantage of precise control over neck

containers also have good gas and

details, wall thickness and weight.

solvent barrier properties and so can

contents and filling line), packaging (shelf height) and presentation (labelling

be expensive, however, so machines are

be used to package aggressive foods,

using sleeves or print, for example).

often dedicated to a single product.

different industries. EBM is favourable for many

variety of shapes in an extensive choice of materials. Containers can be molded

with integral handles and multiple layered walls. IBM is a precise process that

EBM is used mainly in the medical,

IBM is utilized especially for consumer packaging and medical packaging (medicine bottles, tablet and diagnostic bottles and vials). ISBM is predominant in the personal

DESIGN OPPORTUNITIES

Cycle time is very rapid. A single mold

Labour costs are low, as production is automated. Set-up and changeover can

concentrates and chemicals.

All of the blow molding processes can be

COMPATIBLE MATERIALS

ENVIRONMENTAL IMPACTS

All thermoplastics can be shaped using

All thermoplastic scrap can be directly

is suitable for more demanding

care, agrochemicals, general chemicals,

used to produce thin walled and strong

DESIGN CONSIDERATIONS

applications such as medical containers

food and beverages and pharmaceutical

containers.The neck does not have to

A major difference between these blow

blow molding, but certain materials are

recycled. Process scrap is recycled in-

molding techniques is the capacity that

more suited to each of the technologies.

house. Post-consumer waste can also be

and cosmetic packaging. It is used to

industries to produce carbonated and

be vertical or tubular. Features such as

produce containers with very accurate

soft drink bottles, cooking oil containers,

handles, screw necks and surface texture

each can accommodate. IBM is generally

Typical materials used in the EBM process

recycled and turned into new products.

neck finishes as well as wide mouths.

agrochemical containers, health and oral

can be integrated into all 3 processes.

limited to the production of containers

include polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET) and polyvinyl chloride (PVC), while the IBM process is suitable for PP and HDPE

Recycled PET is used in the production of

ISBM is typically used to produce high

hygiene products, bathroom and toiletry

The principal reason to select I BM

between 3 ml and 1 litre (0.005-1.760

quality glass clear PET containers such as

products, and a number of other food

is that there is more control over wall

pints) and ISBM can produce containers

water bottles. The injection cycle ensures

application containers.

thickness and neck details.This means

between 50 ml and 5 litres (0.088-8.799

certain items of clothing, for example.

Blow molding plastics is more energy efficient than glassblowing.

"ase Study

Extrusion blow molding a cleaning agent container The PE polymer granules are stored in a

(116 psi) forcing the parison to take the shape

communal hopper and coloured individually

of the mold (image 4). The molds separate

(image io). The finished product is packaged

for each machine (image i). In this case a

to reveal the blown part with the blow rods

and shipped.

small percentage of blue granules are added

still inserted (image 5). The rods retract and

just prior to extrusion. The extrusion process

the part is deflashed with a profiled trimmer

is continuous and produces an even wall

(image 6).

thickness parison (image 2). The 2 halves of

4

Each batch is conveyed from the blow

the mold close around the parison to form a

molding machine to labelling and capping via

seal and the parison is cut to length (image

pressure testing (image 7). The EBM bottles

3). A blow rod is then inserted into the neck,

pass through the filling line (image 8). The

and air is blown into the mold at 8 bar

caps are screwed on automatically (image 9)

and the labels adhesive bonded to the bottle

Injection Blow Molding Process

Blowing mold

Polymer granules

ection blow molding a roll-on deodorant bottle Conventional injection screw and barrel assembly Pre-form mold Stage 2: Blowing

The polished core rods are prepared so the

when it makes contact with the relatively

pre-forms can be injection molded onto

cooler walls of the mold (image 3). The parts

them (image i). Each core rod is inserted

are stripped from the core rods (image 4),

into a split mold and hot molten white PP is

counted by a laser sensor (image 5) and

molded around it. The necl< is fully formed

pressure tested (image 6). The parts (image

(image 2). The parts are rotated through

7) are then fed into a filling and capping

120° and are inserted into the blowing

system similar to the EBM process.

mold. Air is blown in through the core rod Stripper

Stage 1: injection molding the pre-form

and the plastic is forced to take the shape of the mold cavity. The polymer solidifies

Stage 3: Stripping

TECHNICAL DESCRIPTION The IBM process is based on a rotary table

blowing station. In stage 2, air is blown into

that transfers the parts onto each stage

the pre-form forcing the parison to take the

in the process. In stage 1, a pre-form is

shape of the mold. In stage 3. after sufficient

injection molded over a core rod with

cooling, the part is rotated through 120° and

finished neck details. The pre-form and

stripped from the core rod complete. No

Staged: Final product

core rod are transferred through 120° to the trimming or deflashing is needed.

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Featured Manufacturer Polimoon www.poiimoon.com

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Case Study

Injection stretch blow molding a chemical container The pre-form is injection molded over a

and blown to form the container (Image 3),

core rod, which is removed prior to blowing.

The blown product is ejected and does not

The injection molded part is thin walled,

require any trimming. It is demolded (image

as demonstrated by the operator (Image i).

4), pressure tested (image 5) and a handle

There is not usually operator contact with

is fitted around the neck of the injection

the parts during production. The pre-form

molded container, using an annular snap

is transferred to the blow molds (image 2),

fit (image 6).The container is then sent for

The molds close around the pre-form and it

capping (image 7).

is simultaneously stretched longitudinally

TECHNICAL DESCRIPTION In stage 1, the ISBM process uses the same technique as IBM, In that the pre¬ form is injection molded over a core rod. In stage 2, however, in ISBM the core rod is removed and replaced by a stretch rod. The pre-form is inserted

into the blow mold, which is clamped shut. In stage 3, air is blown in through the stretch rod, which simultaneously

Injection Stretch Blow Molding Process

orientates the pre-form longitudinally. In stage 4, the mold opens and the parts are stripped from the stretch rod. „ . Air blown Core rod

Stretch Air blown in—fj Molds separate

rod

Blown part

Injection molded pre-form Pre-form stretched longitudinally Stage 1: Injection Stage 2: Pre-form molded pre-form stretched and blown

Stage 3: Blowing cycle

8

Blown part ejected Featured Manufacturer Polimoon

Staged: Demolded and stripped

www.polimoon.com 7

Forming Technology

Thermoforming In this group of processes, thermoplastic sheet materials are formed with the use of heat and pressure. Low pressures are inexpensive and versatile, whereas higher pressures can produce surface finishes and details similar to injection molding.

Costs

Typical Applications

Suitability

• Low to moderate tooling costs • Low to moderate unit costs, roughly 3 times material cost

• Baths and shower trays • Packaging • Transportation and aerospace interiors

• Roll fed; batch to mass production • Sheet fed: one-off to batch production

Quality • Depends on material, pressure and technique

Related Processes • Composite laminating • Injection molding • Rotation and blow molding

Speed • Roll fed cycle time: 10 seconds to 1 minute • Sheet fed cycle time: 1-8 minutes

INTRODUCTION

while they are still hot. This complicated

There are 2 distinct categories of

process is more expensive than

finishes similarto injection molding.

thermoforming: sheet fed androli fed.

conventional thermoforming.

The tooling is more expensive, but for

Pressure forming can produce surface

Above left Textured light diffuser manufactured by

Above

vacuum forming.

sheet thermoforming.

Foam filledTerracover®

ice pallet made by twin

some applications it will be less than

Sheet fed thermoforming is for heavy duty applications, such as pallets, baths,

TYPICAL APPLICATIONS

shower trays and luggage.The sheet

Thermoforming is used extensively to

single-sided tool is used, as opposed to

material is typically cut to size and

produce everything from disposable

matched tooling which is required for

loaded by hand. Roll fed processes, on the

food packaging to heavy-duty returnable

injection molding.

other hand, are supplied by a roll of sheet

transit packaging. Some typical examples

for injection molding.This is because a

Twin sheet thermoforming is used to

Pressure forming produces a fine surface finish with excellent

material from areel. It is sometimes

include clear plastic point-of-sale

produce 3D hollow geometries. Similar

referred to as the 'in-line' process because

packaging,clamshell packaging, cosmetic

parts can be produced by blow molding

it thermoforms, trims and stacks in a

trays, drinking cups and briefcases.

(page 22) and rotation molding (page 36), yet the benefit of thermoforming is that

Thermoforming is typically carried out

lighting diffusers; bath and shower trays;

it is ideal for large and flat panels. Also,

on a single mold. In vacuum forming the

forming, pressure forming, plug-assisted

garden pots; signage; vending machines;

the 2 sides are not limited to the same

mold can be made from metal, wood

forming and twin sheet thermoforming.

small andlargetanks;motorcycle

colour or even type of material.

continuous operation. Thermoforming includes vacuum

This process is also used to produce

reproduction of detail.

DESIGN OPPORTUNITIES

or resin. Wood and resin are ideal for

fairings; interiors for cars, aeroplanes and

Material developments mean that

least expensive of these sheet forming

trains;housing for consumer electronics;

twin sheet thermoformed products will

A resin tool will last between io and

processes. A sheet of hot plastic is blown

and protective head gear.

sometimes have suitable characteristics

500 cycles, depending on complexity of

Vacuum forming is the simplest and

into a bubble and then sucked onto the

Blister packaging (bubble wrap) is

prototyping andlow volume production.

for parts that were previously made by

shape. For more products, aluminium

composite laminating (page 206).

molds are cast or machined.

surface of the tool. It is a single-sided

made by thermoforming. It is produced

tool and so only one side of the plastic

continuously on a roller, which is the

will be affected by its surface. In pressure

vacuum former, and is laminated to

QUALITY

inserts can be used to form re-entrant

forming the hot softened sheet is forced

seal air into the individual blisters

Heating and forming a sheet of

angles.They are typically inserted

into the mold with pressure. Higher

and provide protective cushioning for

thermoplastic stretches it.Aproperly

and removed manually. Routing or

pressure means that more complex

packaged goods.

designed mold will pull it in a uniform

cutting into the part after molding

Vacuum forming tooling can be

manner. Otherwise, the properties of the

can sometimes produce the same

including surface textures. For relatively

very inexpensive and so is suitable for

material will remain largely unchanged.

effect. Otherwise, parts can be molded

low volumes this process is capable of

prototypin g an d 10w volum e product! on.

Thus a combination of the mold finish,

separately and welded together.

and intricate details can be molded,

molding pressure and material will

producing parts similarto injection

molding (page 50). The above 2 processes are suited

Similarto othermolding operations

RELATED PROCESSES Low pressure thermoforming techniques

determine surface finish.

The side of thermoformed plastic

Many thermoplastic materials are suitable.Therefore, there are numerous decorative and functional opportunities

to forming shallow sheet geometries.

are versatile and inexpensive.This

sheet that comes into contact with

associated with each of them. Also,

For deep profiles the process is plug

is because the plastic is formed as

the tool will have an inferior finish

materials have been developed

assisted.The role of the plug is to push

a softened sheet, as opposed to a

to pressure formed parts. However,

forthermoforming.These include

the softened material into the recess,

mass of molten material.This sets

the reverse side will be smooth and

preprinted sheets (such as carbon

stretching it evenly.

thermoforming apart from many

unmarked.Therefore, parts are

fibre-effect), which are a coextrusion of

other plastic forming processes.

generally designed so that the

acrylonitrile butadiene styrene (ABS) and

the qualities of these processes with

However, the use of sheet increases

side that came into contact with the

poly methyl methacrylate (PMMA) with

the production of hollow parts. In

the material cost slightly.To minimize

tool is concealed in application.Tools

aprintedfilm sandwiched in between.

essence, 2 sheets are thermoformed

this some factories extrude their own

can be outward (male) or inward

These materials are usually affected by a

simultaneously and bonded together

materials.

(female) curving.

minimum order in the region of 3 tonnes.

Twin sheet thermoforming combines

o ~n o

TECHNICAL DESCRIPTION

Thermoforming Processes

Plug-assisted forming

Vacuum forming is a straightforward Heated and softened sheet

process and provides the foundation for the other thermoforming techniques. A sheet of

Sheet conforms to mold profile

Clamp ring Mold pushes up into sheet

material is heated to its softening point. This is different for each material. For example,

Female mold

the softening point of polystyrene (PS) is 127-182°C (261-360°F| and PP is U3-165°C

Air channels

(289-329°F). Certain materials, such as

1—

\ v y

¦1

It!

1——

Plug-assisted preheated sheet Forming the vacuum

HIPS, have a larger operating window (that

Twin sheet thermoforming

is, the temperature range in which they are

Air sucked out from both sides

formable), which makes them much easier

Upper mold

to thermoform.

fiH]

1 \

/

The softened plastic sheet is blown into a bubble, which stretches it in a uniform manner. The airflow is then reversed and

the tool is pushed up into the sheet. The Lower mold

material is drawn onto the surface of the

mold by vacuum at about 0.96 bar (14 psi).

Preheated sheet

Forming the vacuum Preheated sheets

To assist the flow of air, channels are drilled into the tool. They are located in recesses

Plug-assisted forming is used to bring

This forms an enclosed and thin walled

and across the surface of the mold to extract

the benefits of male mold forming to female

product. Both sides of the product are

the air as efficiently as possible.

parts because blowing a softened sheet into

functional, unlike the single sheet processes.

Pressure forming is the reverse of

a bubble stretches it evenly while draping

The machines are rotary. The clamps

vacuum forming; the sheet is formed onto

the sheet into a female mold produces more

transfer the sheet into the heating chamber,

the surface of the mold under approximately

localized stretching. The plug stretches

where it is raised to softening temperature;

6.9 bar (100 psi) of air pressure. This

the sheet prior to forming and so ensures

it Is then thermoformed and clamped; and

means that a greater level of detail can be

that there is adequate wall thickness for

finally rotated to the unloading station. The

achieved. Surface details on the mold will

deep profiles. Otherwise the material

2 sheets are thermoformed individually, one

be reproduced with much more accuracy

will tear. When the air Is drawn out, the

above the other. Once fully formed they are

than vacuum forming. Surface finish can be

sheet conforms to the mold profile and the

clamped together. Residual heat from the

more accurately controlled and is therefore

hydraulic plug retracts.

functional. However, like vacuum forming only one side of the sheet will be functional.

In twin sheet thermoforming, 2 sheets are thermoformed and clamped together.

Textures are sometimes necessary

Twin sheet thermoforming

COMPATIBLE MATERIALS

on the surface of the mold to assist the

Although almost all thermoplastic

flow of air and avoid air pockets forming.

materials can be thermoformed, the

These are known as 'open textures'.

most common are ABS, polyethylene

Sheet fed thermoforming is used to

terephthalate (PET) (including PETG, which is PET modified with glycol),

Top Above

is supplied by a reel and so is limited to

polypropylene (PP), polycarbonate (PC), high impact polystyrene (HIPS) andhigh

moldmaking material, thermoforming shaped by CNC machining, produced in a single

thermoforming enables the bond to form

o.i mm to 2.5 mm (0.004-0.1 in.).The size

density polyethylene (H DPE).The glycol in

with prolonged contact. The bond has similar

of part is typically restricted to 1.5 x 3.5 m

PETG reduces brittleness and premature

Textured design feature

strength to the parent material.

(5 x 11.5 ft), although some machines are

ageing. PETG is clear (almost like PC)

vacuum formed on mold

capable of dealing with sheets of 2.5 X4m (8 x13 ft).

and is therefore often the material of

made of microporous

process sheet materials ranging from i mm to 12 mm (0.04-0.47 in.). Roll fed

Draft angles are essential when Multilayered materials are

Forming the vacuum and clamping

walled parts. It is not usually practical

th erm oformi n g over protrusi on s, or m al e

choice for lighting diffusers and medical

Microporous aluminium Carpet covered

operation.

Middle

aluminium.

packaging, for example. of parts per minute. Roll fed machines

coextruded to provide benefits: for

produces 3D hollow parts.This has

forthe depth to exceed the diameter.

molds. This is because the heated plastic

COSTS

example, providing a barrier to moisture

added benefits including lightness

Materials can be stretched more evenly

sheet is expanded; as it cools it will shrink

Tooling costs are typically low to

are generally loaded by hand. This

or bacteria; different colours; and

and rigidity, insulation and 2 separate

over the surface of a deep profile using

by up to 2%. Different materials have

moderate, depending on the size,

increases labour costs.

sandwiching recycled material between

m ateri al s (upper an d 1 ower). Sin gl e sheet thermoforming is typically limited

plug-assisted forming.

films of virgin (aesthetic) material to reduce energy.

to only a single side of functionality.

mold will leave slight pimples.These

Textured sheets can be thermoformed

(see image, page 31, above left).Typically sheets are textured on one side and

Air channels on the surface of the

are automated, while sheet fed machines

different levels of shrinkage: for example,

complexity and quantity of parts. The

ABS will shrink 0,6% and H DPE 2%. A draft

most expensive tools are machined

ENVIRONMENTAL IMPACTS

angle of 2° is usually recommended.

aluminium.Tooling for pressure forming

This process Is only used to form

Twin sheet, on the other hand, provides

can be eliminated on aesthetic surfaces

is 30-50% more expensive than vacuum

thermoplastic materials, so the majority

functional surfaces on both sides.

with the use of microporous aluminium

thermoformed, and this will be more

forming, but is still considerably cheaper

of scrap can be recycled. Kaysersberg

molds (see image, top).This material

prominent in deeper and undulating

Pi asti cs, wh o provi ded th e extrudl n g the sheet material case study (page 34),

Foam can be molded into twin sheet,

The material stretches as it Is

so the smooth side is formed against

or be injected post-forming for added

has a much shorter molding lifespan

profiles.Therefore, care must be taken

than tooling for injection molding. The speed of thermoforming depends

the m old. There is a range of standard

rigidity and strength (see image, page

because the pores clog up eventually.

to avoid sharp corners and points where

on the selected process and material

produce only 1.4% scrap material; the rest

textures, which are cast or extruded by

31, above, right).

However, they are very useful for design

three corners meet.These will cause

thickness. Sheet fed processes typically

is recycled.

details (see image, middle), which would

excessive thinning and thus weak points.

the material manufacturer. Examples

produce 1-8 parts per minute. Roll

include frosted, haircell, lens, embossed

DESIGN CONSIDERATIONS

otherwise require hundreds of air

fed machines are generally faster and

and relief.

Thermoforming is ideal for shallow thin

channels (holes).

multiple cavity tools can make hundreds

ixtruding the sheet material aysersberg Plastics extrude sheet material

in operation the sheet is pulled through

to length. The finished sheets are stacked in

ar thermoforming. They can very accurately

the rollers. However, when the process

preparation for thermoforming.

Dntrol the quality of the material and mal :=> [=> i=> Flow and heating of polymer granules Costs Solidified part ejected

• Very high tooling costs but depends on complexity and number of cavities • Very low unit costs

Injection molding process

; Quality | • Very high surface finish I • Highly repeatable process

Speed

DESIGN OPPORTUNITIES

• injection cycle time is generally between 30 and 60 seconds

So much is practically possible with injection molding that restrictions generally come down to economics. The process is least expensive when using

INTRODUCTION

housingofcon sum erelectronics,plastic

of grades, colours and hardnesses. It can

a simple split mold. Most expensive

injection molding is a widely used and

cookware handles and buttons.

be solid or foamed. Reaction injection

are very complex shapes, which are

well-developed process that is excellent

for rapid production of identical parts

RELATED PROCESSES

Ejection cycle

TECHNICAL DESCRIPTION Polymer granules are dried to exactly

are made up of water cooling channels

the right water content and fed into the

[for temperature control), an injection

hopper. Any pigments are added at this

point (gate), runner systems (connecting

stage at between 0.5% and 5% dilution.

parts) and electronic measuring

The material is fed into the barrel,

equipment which continuously monitors

where it is simultaneously heated, mixed

temperature. Good heat dispersal

molding is used for a diverse range of

achievable in a range of sizes, from large

products, including foam moldings for

and moved towards the mold by the

within the tool is essential to ensure the

car bumpers to the tiniest widgets.

rotating action of the Archimedean screw.

steady flow of melted polymer through

The relative suitability of related

upholstering furniture and car seats, and

Retractable cores controlled by cams or

processes depends on factors such as

low volume production of car bumpers

The melted polymer is held In the barrel

the die cavity. To this end, some cores

hydraulics can make undercuts from

products. Accurately engineered tools

momentarily as the pressure builds up

part size and configuration, materials

and dashboards.

are machined from copper, which has

the sides, top or bottom of the tool

ready for injection into the mold cavity.

and high injection pressures are essential

being used,functional and aesthetic

with tight tolerances. It is used to create a huge diversity of our day-to-day plastic

for achieving excellent surface finish and reproduction of detail. Consequently, this

requirements, and budget.

Although injection molding is

simultaneously and will not affect the

QUALITY

cost significantly, depending on the

the melted plastic is injected into the die

The high pressures used during injection

complexity of the action.

cavity. Cycle time is determined by the

process is suitable only for high volume

very often the most desirable process

molding ensure good surface finish,

production runs.

due to its repeatability and speed,

There are many different variations

The least expensive injection molding tooling consists of 2 halves, known as the

size of the part and how long the polymer

male tool and female tool. But engineers

fine reproduction of detail and, most

are often integrated into the molding

takes to resolidify, and is usually between

and toolmakers are constantly pushing

cycle, so eliminating finishing processes

30 and 60 seconds.

the boundaries of the process with more

thermoforming (page 30) is a suitable

importantly, excellent repeatability.

alternative for certain sheet geometries,

of the most popular include gas-assisted

and extrusion Is more cost-effective

The downside of the high pressure is that the resolidified polymer has a

injection molding (page 58), multishot injection molding (page 60) and in-mold decoration (page 62).

for the production of continuous

tendency to shrink and warp. These

pearlescent,thermochromatic and

profiles.

defects can be designed out using rib

photochromatic effects, as well as vibrant

by injection molding can be prototyped

much better conductive qualities than aluminium or steel.

In-mold and insert film decoration

on injection molding technology. Some

Parts that will ultimately be made

The correct pressure is achieved and

details and careful flow analysis. Surface defects can include sink

such as printing. There is also a range of pigments available to produce metallic,

fluorescent and regular colour ranges. Inserts and snap-fits can be molded into

Clamping pressure Is maintained

multiple gates and multishot injection

shrinkage once the part is ejected.

of contrasting materials.

To eject the part, the tools move apart, the cores retract and force is applied

by the ejector pins to separate the part from the surface of the tool. The part is

TYPICAL APPLICATIONS

and produced in low volumes by vacuum

marks, weld lines and streaks of

Injection-molded parts can be found

pigment.Sink marks occur on the

in every market sector, in particular in

casting (page 40) and reaction injection molding (page 64). Both of these

surface opposite a rib detail, and

combine up to 6 materials in one

autom oti ve, i n dustri al an d h ous eh ol d

processes are used to form polyurethane

weld lines appear where the material

product.The combination possibilities

products.They include shopping baskets,

resin (PUR).This is a thermosetting

machined from either aluminium or tool

is forced to flow around obstacles, such

include density,rigidity, colour, texture

stationery, garden furniture,keypads, the

steel. The tools are very complex parts

plastic that Is available in a wide range

as holes and recesses.

and varying levels of transparency.

of the injection molding process. They

the product to assist assembly.

Multishot injection molding can

complex tooling, retractable cores,

after injection to minimize warpage and

dispensed onto a conveyor belt or holding container, sometimes by a robotic arm. Tools and cores are generally

DESIGN CONSIDERATIONS

Case Study

Designing for Injection molding is a

Manufacturing and assembling a Pedalite

complex and demanding task that involves designers, polymer specialists, engineers, toolmakers and molders. Full

This bicycle pedal light is powered by an

ensuring a 'right first time' product. The

collaboration by these experts will help

energy storage capacitor and microgenerator

technically challenging combined overmold

anatomy of the injection-molded parts as

realize the many benefits of this process.

rather than any form of chemical battery.

assembly, for instance, was approved at the

well as the internal mechanisms and parts,

It was designed by Product Partners, in

first-off tool trials.

Injection molding operates at high

The cutaway drawing (below) shows the

injection-molded casings very often have to

temperaturesandinjectsplasticized

conjunction with the ciient (Pedalite Limited),

material into the die cavity at high

toolmaker/molder (ENL Limited), gearbox

feasible Davall Gears were recruited to

case, specific spindle bearings have been used

pressure.This means that problems

manufacturer (Davall Gears) and polymer

provide expertise in gear ratios, gear

to satisfy legislations and the gear system is

distributor (Distrupol Limited).

detail design, materials specification and

designed for optimum energy generation.

can occur as a result of shrinkage and

A dose working partnership with ENL

stress build-up. Shrinkage can result in warpage, distortion, cracking and sink marks. Stress can build up in areas with

die cavity and so the material must be

fed into the thickest wall section and finish in the areas with the thinnest wall sections. For best results wall thickness should be uniform, or at least within io%. Uneven wall sections will

gloss areas are more expensive to

as mold preparation anddemolding,

produce different rates of cooling, which

produce than matt or textured ones.

increase the costs significantly.

cause the part to warp. The factors

that determine optimal wall thickness

COMPATIBLE MATERIALS

ENVIRONMENTAL IMPACTS

include cost,functional requirements

Almost all thermoplastic materials can

Thermoplastic scrap can be directly

and molding consideration.

be injection molded. It is also possible to

recycled in this process. Some

mold certain thermosetting plastics and

applications, such as medical andfood

metal powders in a polymer matrix.

packaging, require a high level of virgin material, whereas garden furniture may

of the part, while decreasing wall thickness; and secondly, they aid the

COSTS

require only 50% virgin material for

flow of material during molding. Ribs

Tooling costs are very high and depend

adequate structural integrity,hygiene

should not exceed 5 times the height of

on the number of cavities and cores and

and colouring capability.

the wall thickness. Therefore, it is often

the complexity of design. Injection molding can produce small parts very rapidly, especially because

Injection molded plastic is commonly associated with mass produced short term products, such as disposables.

All protruding features are treated as

multicavity tools can be used to increase

However, it is possible to design products

ribs and must be 'tied-in' (connected) to

production rates dramatically. Cycle time

so that they can be disassembled

the walls of the part to reduce air traps

is between 30 and 60 seconds, even for

easily, which is advantageous for both

and possible stress concentration points.

multiple cavity tools. Larger parts have

maintenance and recycling. If different

Holes and recesses are often integrated

longer cycle times, especially because the

types of materials are used, then snap

in part design in order to avoid costly

polymer will take longer to resolidify and so will need to be held in the tool while

fits and other mechanical fasteners

it cools.

and dispose of the parts with minimal

Injection molded parts are often finished with afine texture, which disguises surface imperfections. Large

about materials selection andmoldflow

lines and so forth.

path of least resistance as it enters the

secondary operations.

Polymer distributor Distrupol was consulted

problems of sinkage, flow marks, weid

The injected plastic will follow the

as opposed to fewer deep ribs.

MOLDFLOW ANALYSIS

and self-lubrication properties.

components in CAD to reduce potential

ejection from the tool.

recommended to use lots of shallow ribs,

chosen for its exceptional wear characteristics

successfully translated through the design,

design led to the modification of the

0.5° to avoid stressing the part during

design: firstly, they increase the strength

manufacture. Polyamide (PA) nylon was

analysis. Feedback on the developing

too small. Draft angles should be at least

Ribs serve a dual function in part

accommodate a fixed-space package. In this

ensured Product Partners'ideas were

development and toolmaking process,

sharp corners and draft angles that are

To ensure the gearbox concept was

Labour costs are relatively low. However,manual operations, such

make it more convenient to disassemble environmental impact.

MOLDING THE PEDALITE

ASSEMBLING THE PEDALITE

The raw material 1s a glass-filled nylon

There are many parts that make up the

that is white in its raw state, if a colour

Pedalite (see image, page 54). All of the

is required, then pigment is added. In

plastic parts are injection molded.The

this case a small quantity of Clariant

bearing locator is a friction fit, which

masterbatch yellow was used (Image i).

requires more precise tolerance than

The end result is a surprisingly vivid

can be achieved with injection molding.

yellow colouring.

Therefore, it is drilled post-forming

In normal operations, the injection

(image 6) and the bearing locator and

molding process takes place behind a

bearing inserted. The overmolded end

screen within the machine (image 2),

cap is fixed to the pedal housing with

but for the purposes of this case study

screw fixings (image 7). The reflectors

the dies are shown in close-up with the

snap fit into place (image 8), ensuring

screen open.

that all the components are held together

The polymer is melted and mixed

securely.The snap fits can be released so

before injection into the die cavity. Once

that the Pedalite can be dismantled for

the die cavity has been filled, packed

maintenance and recycling (image 9).

and clamped, and the polymer has

The finished product is installed by

resolidified, the male and female halves

conventional means onto a bicycle

of the mold move apart. The product

(image 10).

is held in the moving tool by the upper

Cycle pedal design is subject to

and lower retractable cores and the 2

considerable safety and technical

side-action cores (image 3), The injection

restrictions. Pedalite eliminates the

point is indicated by the sprue, which has

expense and inconvenience of battery

remained intact, to be removed either

replacement, as well as the negative

by hand or robotically. The 4 cores are

environmental Impact of battery disposal.

retracted in sequence, to reveal the true

The 24/7 light output of Pedalite does

complexity of this molding (image 4).

not replace existing cycle safety lighting,

Finally, the part is ejected from the mold

but supplements it and also provides a

by a series of ejector pins (image 5).

unique light 'signature' (lights moving up and down) that helps motorists judge their distance from the cyclist.

Featured Manufacturer

ENL www.enl.co.uk IO

ase Study

Moldflow analysis Prior to manufacturing, Moldflow software is

The examples below illustrate analysis of flow,

used to analyse and maximize the efficiency

warp, fibre orientation, cooling and stress,

the automotive hubcap for PolyOne (image 3)

This analysis too] is used to predict

it was possible to reduce stress and make sure

shrinkage and warping, which are the

all types of plastic injection molding and

MPI/FLOW

there were no air traps in critical areas.The

result of stresses built up during the

metal die casting. It brings together part

MPI/Flow simulates the filling and packing

colour scale indicates bulk stress.

molding process. The Information is

design, material selection, mold design and

phases in the molding process, helping to

The colour scale on the automotive

processing conditions to determine the

predict the behaviour of the material as it

Interior product manufactured by Resinex

processing parameters to minimize

manufacturability of the part. This reduces

flows through the die cavity. This is used to

and Gaertner & Lang (image 4) indicates

potential problems.

the costs and time delays associated with

optimize the location of the gate, balance

fill time in seconds. Appearance is very

otherwise unforeseen manufacturing

runner systems and predict potential

Important, so the flow analysis software

problems. It also maximizes the efficiency

problems. Different versions are used

was used to eliminate weld lines and colour

switchboard cabin (image 5). The analysis

of production and can reduce material

to simulate different plastic and metal

variation in critical areas. This was achieved

found that by reducing wall thickness

consumption with significant savings.

molding techniques.

by changing the location of the gate and

warp could be reduced by go%.

of a design. The software is suitable for

A 3D model of the required part is

The MPI/Flow is here demonstrated on

By changing the location of the gate on

MPI/WARP

used to specify material selection and

Any more than 5 mm (0.2 in.) warp

was unacceptable on this Efen electronic

On the CAD model for a Jokon

temperature of the runner system.

generated in a suitable computer aided

3 products. Two stages of an Abtec part are

automotive lamp assembly (image 6), it

design (CAD) or computer aided engineering

simulated (images 1 and 2) to demonstrate

was essential that the part did not warp

(CAE) software package.

confidence of fill, which is colour coded, MPI/

so that it would maintain a water-tight

Moldflow is a predictive analysis tool

Flow was used to simulate various

seal in application. Warpage was reduced

used to simulate the 3D model in production

gate positions and runner system

by 50% by optimizing wall thickness

to analyse filling, packing and cooling.

configurations.

(images 7 and 8).

Confidence Of Fill

MPI/COOL

Confidence Of Fill

MPI/Cool 1s used to analyse the design

Low 1

Low

of mold cooling circuits. Uniform cooling is important to make sure that the part does not warp and to minimize cycle times.

A filter housing manufactured by Hozelock shows the configuration of the mold cooling circuits (images 9 High

to 11). Changing the layout of the circuit reduced cycle time by 2 seconds and so saved more than 4% of the production cost; reducing the wall thickness reduced cycle time by 7.3 seconds and shot weight

[sec]

by 19,6%, saving 24% of the production costs. Combining the 2 produced 26.1% overall savings.

Featured Manufacturer

Moldflow www. m 0 Id flow, com

TECHNICAL DESCRIPTION

Gas-Assisted Injection Molding Process

Gas-assisted injection molding Partially filled die cavity

techniques were first used in mass production in 1985. Since then the

technology has steadily improved and

The Air Chair was designed by Jasper

is now into the third generation of development. Initially it was developed to overcome the problem of sink marks

Gas injection molding the Magis Air Chair

Modified injection molding equipment

caused by shrinking. A smalt amount of

gas was blown in during the injection polymer cooled before the tool opened.

Stage 1: Conventional injection molding

With very precise computer control,

it is now possible to gas fill long and Air pocket

complex moldings. Each cycle will be slightly different because the computer

breaching it. Finally, the gas is injected to

skin is aesthetic and therefore should not

produce a hollow section and make it rigid

(image i).The gas injection molding sequence

be filled. However, unfilled PP is not strong

but lightweight.

takes approximately 3 minutes (images 2-5).

enough to make the entire structure.

The sample cut from the leg of the Air

cycle to apply internal pressure as the

Two materials are used because the outer

Morrison and production began in 2000

The 2 layers of material in this sample are

The gas injection molding technique produces a plastic chair with a very good

Table shows 2 technologies (image 6). The

produced in a similar way to gas injection.

surface finish. It weighs only 4.5 kg (9.92 lb)

first is gas injection, which creates the hollow

The outer skin is injected first. The glass

and is capable of withstanding heavy use.

profile.The second technology is the thin skin

filled PP is injected behind it in a technique

around the outside of the material: there is a

known as 'packing out'. The second material

clear division between the outer unfilled PP

acts like a bubble of air and pushes the first

and the glass filled structural internal PP.

material further into the die cavity without

makes adjustments for slight changes in material properties and flow.

The process uses modified injection Injection continues

molding equipment, in stage 1, plastic

is injected into the mold cavity but does not completely fill it. In stage 2, gas is

Gas injected

injected, which forms a bubble In the molten plastic and forces It Into the

Stage 2: Gas injected

extremities of the mold. The plastic and gas injection cycles overlap. This

Finished part

produces a more even wall thickness

because as more plastic is injected the air pressure pushes It through the mold like a viscous bubble. The gas bubble maintains equal pressure even over long and narrow profiles. Wall thickness can be 3 mm (0.118 in.) or more. In stage 3, as the plastic cools and solidifies, the gas pressure is

Stage 3: Finished product

maintained. This minimizes shrinkage.

Less pressure is applied to the plastic because the gas assists its flow around the die cavity.

Featured Company Magis www.magisdesign.com

Multishot Injection Molding Process

Multishot injection molding a handheld gas detector Polymer B granules

This product is molded by Hymid for Crowcon.

molded over it. The TPE provides integral

are inserted into the mold by hand prior to

It is a handheld gas detection unit (image

features with hermetic seals, such as flexible

each injection cycle.

i). Multishot injection molding has very

buttons and a seal between the 2 halves.

important benefits that are essential for Platen rotates 180°

Rotating platen

Static platen

Part A rotated into die cavity ready for njection of polymer B

Moving and rotating platen

The mold half with the moldings rotates

The finished moldings are stacked (image 7) ready for assembly. The integral and

the effectiveness of this device, which is

through 180° (images 3 and 4), In doing so, it

flexible button detail is shown in the final

potentially lifesaving.The part is made up of

brings the solidified PC into alignment with

product (image 8).

a water clear polycarbonate (PC) body and

the second injection cavity. Then the finished

thermoplastic electrometric (TPE) covering.

molding is ejected (image 5) ready for the

The features of these materials are combined

next injection cycle to commence.

by multishot injection molding. This is a tricky combination because the

The knurled metal inserts (image 6) are incorporated in the PC by overmolding,These

materials operate at different temperatures.

Therefore, the runner system for the PC is heated with oil, whereas the TPE runner is cooled with water. Molten polymer A injected into lower die cavity

Of the 2 die cavities (image 2), the

Molten polymer B injection molded over solidified polymer A

Empty die cavity Stage 3: Rotation

Stage 2: Ejection

Stage 1: Injection

closest has just been injected with water clear PC, This gives the product rigidity, toughness and impact resistance. The

farthest die cavity is the PC with aTPE

TECHNICAL DESCRIPTION Injection molding 2 or more plastics together

In stage 1, polymers A and B are injected

In stage 2, the molds separate and the

is known as multishot or overmolding. The

at the same time Into different die cavities:

sprue is removed from molded polymer A.

difference is that multishot is carried out

polymer A is injected into the lower die

Meanwhile the finished molding is ejected

in the same tool. Overmolding is a term

cavity; meanwhile, polymer B is Injected

from the upper die cavity. The rotating

used to describe injection molding over

over a previously molded polymer A in the

platen spins to align molded polymer A with

any preformed material, including another

upper cavity. The molten polymers form a

the upper die cavity. In stage 3, the mold

thermoplastic, or metal insert, for example.

strong bond because they are fused together

closes again and the sequence of operations

under pressure.

is repeated.

The process of multishot Injection molding uses conventional Injection molding machines. It is possible to multishot up to 6 different materials simultaneously,

each one into a different die cavity in the same tool.

The tool is made up of 2 halves: one Is mounted onto a static platen, the other onto a rotating platen. Like conventional injection, this process can have complex cores, Inserts and other features.

Featured Manufacturer

Hymid Multi-Shot www.hymid.co,uk

TECHNICAL DESCRIPTION

In-Mold Decoration Process

Case Study

The in-mold decoration process is used Printed PC film loaded

to apply print to plastic products during

In-mold decoration Luceplan Lightdisc

injection molding, thus eliminating secondary operations such as printing and spraying. However, the cycle time of

injection molding is increased slightly. The process is used in the production of nearly every modern mobile phone, camera and other small injection molded product.

In stage 1, a printed PC film is loaded

Stage 1: Film inserted

side of the mold is textured to provide the

fixed in place (image 8). Then the 2 halves of

of the Luceplan Lightdisc (image i). It was

diffusing effect in the light (image 4). The

the Lightdisc are screwed together (image 9).

designed by Alberto Meda and Paolo Rizzatto

mold is clamped shut under 600 tonnes

The fixings are covered with a snap fit

in 2002. By incorporating in-mold decoration,

(66i US tons) of hydraulic pressure and the

enclosure (image 10), which means the whole

the diffuser acts as shade, too. Graphics and

injection molding takes place (image 5).The

product can be taken apart for maintenance

instructions are included on the in-mold film

part is demoldedby hand (image 6), but this

and recycling.

and this eliminates all secondary printing.

can also be carried out using a robot.

The process is similar to conventional

into the die cavity prior to injection molding. The print side is placed

This case study demonstrates the production

Plastic injected behind film

inwards, so that when it is injection

This finished molding is inspected prior

injection molding, except that a printed film

to assembly (image 7). Screw bosses are

is placed into the die cavity.

incorporated into the injection molding,

The film is prepared and placed into the

molded the print will be protected

so the assembly procedure is relatively

mold by hand (images 2 and 3).The opposite

behind a thin film of PC.

straightforward. The electrics are inserted and

In stage 2, when the hot plastic is injected in the die cavity, it bonds with

Conventional injection molding equipment

the PC film. (This is similar to multishot injection molding.) In stage 3, the film becomes integral with the injection molded plastic and has a seamless finish, with a printed surface.

Stage 2: Conventional Injection molding

If the surface of the mold is not flat or slightly curved then the film is

Finished part with printed surface

thermoformed to fit exactly. When the

hot plastic is injected it is forced against the mold face at pressures between 30

and 17,000 N/cm2 (20-11,720 psi). The pressure is determined by the type of material and surface finish. Another technique, known as insert

film molding, differs because the film is supplied as a continuous sheet. It is

Stage 3: Finished product

sucked into the die cavity by a strong vacuum (similar to the thermoforming process), the mold closes and the injection process follows.

8

Featured Company Luceplan www.Luceplan.com

9

IO

Cold Cure Foam Molding Process Part A: liquid isocyanate Part B: liquid polyol

Upper mold

Forming Technology

Reaction Injection Molding

Lower mold Upper mold raised

Runners Retractable core Steel framework

Bung inserted

Reaction injection molding (RIM) includes cold cure foam Core retracted

molding. Both processes are used to shape thermosetting foam by injecting thermosetting polyurethane resin (PUR) into a mold, where it reacts to form a foamed or solid part. Stage 1; Mold filled

• Low to moderate tooling costs, depending on the size and complexity of molding

Typical Applications

Suitability

• Automotive • Furniture • Sporting goods and toys

• One-off to high volume production

Stage 2: Polyurethane formed

Stage 3: Demolded and trimmed

TECHNICAL DESCRIPTION In stage 1, the molds are cleaned and a release agent is applied. Inserts and frames are then put into place and the

Quality • High quality moldings with good reproduction of detail

Related Processes

Speed

mold Is clamped shut. The 2 ingredients

• CNC machining • Injection molding • Vacuum casting

• Rapid cycle time (5-15 minutes), depending on complexity of molding

that react to form PUR are stored In separate containers. The polyol and

Isocyanate are fed Into the mixing head, where they are combined at high

INTRODUCTION

RIM is chosen a great deal in the

properties of the part are similar to

pressure. The predetermined quantities

injection molding.

of liquid chemicals are dispensed into the

These are low pressure, cold cure

automotive industry for products such as

processes. Cold cure foam molding

bumpers,under-bonnet applications and

is generally attributed to molding PL) R foam for upholstery and sports

car interiors. It is utilized in the medical

QUALITY

they begin to go through a chemical

and aerospace industries for niche

The quality of the surface finish is

exothermic reaction to create PUR.

equipment, whereas RIM covers molding

products and low volume production

determined by the surface of the mold.

mold at a low pressure. As they are mixed

During stage 2 the polymer begins to expand to fill the mold. The only pressure

The tooling can be produced in glass reinforced plastic (GRP), etched or alloyed

on the mold is from the expanding liquid,

RELATED PROCESSES

steel. Even though this is a low pressure

so molds have to be designed and filled to

Bulk foam geometries are also formed

process, the liquid PUR reproduces fine

volume production, this process is

by CNC machining (page 186) orfoam

surface textures and details very well.

commonly used to prototype parts

fabrication.This technique is often

that will be injection molded (page 50) because the tooling is much less

utilized to cover wooden structures in

DESIGN OPPORTUNITIES

upholstery (page 342). Foam molding is

This is an extremely versatile process

expensive than for injection molding,

becoming more widely used, for example,

as the mechanical properties of the

while repeatability and accuracy are high.

in the production of furniture and car

cured PUR can be designed to suit the

seats-new formulations of PURfoam

application.The flexibility of foam can

of the part. The upper and lower sections

TYPICAL APPLICATIONS

producing fewer isocyanates, so they are

range from semi-rigid to very rigid, and

of the mold are separated and the cores

Popular uses include domestic and

therefore less toxic.

the density can be adjusted from 40 kg/

are removed. The mold Is then cleaned

m3 to 400 kg/m3 (2.5-25 lb/ft3).The outer

and prepared for the next cycle.

all types of PUR including foam. In both

runs, too.

processes, the density and structure of PUR are chosen to suit the application.

As well as low, medium and high

commercial furniture such as chairs,

Vacuum casting (page 40) is used to form similar geometries in PUR,

skin andinnerfoam can have contrasting

and cushions.These processes are also

but is typically applied to smaller and

properties to form parts with a rigid skin

suitable for cushioning functions in

more complex shapes. Vacuum casting

andlightweight foam core, for example.

and RIM are chosen to prototype

safety and tactility in toys.

and manufacture low volumes.The

Above

Above

A predetermined measure of polyol and isocyanate is dispensed into a plastic bag to demonstrate the

The 2 liquids react and expand to form lightweight and flexible

expands the runners allow trapped air to

car, train and aeroplane seats, armrests

footwear, such as in the soles, and for

ensure even spread of the polymer while

it is still in its liquid state. As the polymer

RIM is similarto injection molding: parts can be textured and the surface

escape. A bung is Inserted in the gate to maintain internal pressure in the mold.

In stage 3, the product is demolded after 5-15 minutes. Shot and cycle times vary according to the size and complexity

reaction process.

foam.The reaction isi-way,so once the material has been

formed it cannot be modified except by CNC machining.

Case Study

Cold cure foam molding the Eye chair The Eye chair has a parallel Internal core,

the mold through the gate at the top

complex internal steel structure and plastic

(image 3). After 12 minutes the chemical

back plate for upholstery, so has a challenging

reaction is complete and the part can be

geometry for foam molding.

demolded.The 2 halves of the mold are

The first step in the molding cycle is

separated to reveal the foam product

the mold preparation. A release agent is

(image 4). The chair is removed from the

sprayed onto the internal surfaces of the

internal core and checked for any defects

mold (image ij.The steelwork is then loaded

(image 5). Excess flash is then removed

into the mold over the internal core and the

with a rotating trimmer (image 6). This

whole assembly is closed and clamped shut

foam seat is part of the Eye chair (image

(image 2). A predetermined quantity of polyol

7), which is upholstered (page 342) by Boss

and isocyanate are mixed and injected into

Design.

molding) or RRIM (reinforced reaction

be softer and are upholstered or covered.

injection molding). Finally,fibre mats

Closed-cell foams are self-skinning and

and other textiles can be molded in,

used in applications such as armrests.

XI

m > o

o O O r~ a

for improved resistance to tearing and stretching.

COSTS

The molds can be made in various

Tooling costs arelowtomoderate.They

materials, depending on the quantities

are considerably less than when tooling

and required surface finish. GRP is often

for injection molding due to reduced

used to produce molds for prototyping; it

pressure andtemperature.GRPtooling is

is relatively inexpensive and reduces lead

cheaper than aluminium and steel.

times. For production runs above 1,000,

Cycle time is quite rapid (5-15 minutes). Atypical mold will produce

units, aluminium or steel tools are used.

50 components per day.

DESIGN CONSIDERATIONS The size of part that can be molded ranges from minute to very large (up to

significantly. Prototyping and low volume

3 m/10 ft long).The polymer is very liquid

production require more labour Input.

printed with in~mold decoration.

in its non-catalysed state, so will easily

Preformed materials are used to decorate

fl ow aroun d 1 arg e an d complex m ol ds.

the surface of the part, and colour is

A predetermined quantity of PU R is

framework, the foam must be at least

mixed and Injected in each cycle to

10-15 mm (04-0.59 in.) larger, to ensure

ensure minimal waste. Flash has to

plastic molding processes. For example,

the structure is not visible on the surface

be trimmed from the molded part.

both thick and thin wall sections from

of the foam.

RIM has many advantages over other

5 mm (0.2 in.) upwards can be molded

The Eye chair is molded in cold cure MD1

This CAD visual shows the supporting metal framework, which is

are included in the molding for upholstery.

ENVIRONMENTAL IMPACTS

When foam molding over steel

specified by Pantone reference.

Above

Labour costs are low to moderate and automated processes reduce labour costs

Reconstituted foam blocks are often

Incorporated into the molded part to

into the same part. Also, inserts such as

COMPATIBLE MATERIALS

plywood laminates, plastic moldings,

PUR is the most suitable material

threaded bushes and metal structures

because it is available in a range of

during the reaction are harmful and

can be molded into the part (see

densities, colours and hardnesses. It can

known to cause asthma.The polyol/MDI

reduce virgin material consumption. The Isocyanates that are off gassed

formulation of around

overmolded with foam.

image, left). Fibre reinforcement can be

55lC

hardens in about 24 hours.

geometries to thermoforming and 1

temperature and slow dipping speed;

|1^0°F|, so as the tool cools and the wall

RELATED PROCESSES

Case Study

Dip molding a flexible bellow The pre-heated aluminium tools are dipped

ensuring that the viscous liquid does not fold

Compressed air is blown in, which frees the

in dilute silicone solution (image i).Ttie

over on itself and trap air (image 3). After 45

plastic part from the metal and allows it to be

silicone promotes the flow of liquid over the

seconds the tank is lowered to reveal the dip

removed (image 7).

surface of the tool and then acts as a release

molded parts (image 4), which are quickly

The inside of the final part is matt

agent once it has solidified. The water steams

inverted (image 5) and placed in an oven to

(replicating the tool) and the outside is

from the surface of the tool to leave a very

fully cure.

smooth and glossy (image 8).

thin film of concentrated silicone. The tools are mounted above the tank

They are removed from the oven and

lowered into a bath of cold water (image 6).

of room temperature liquid plastisol PVC

The water lowers the temperature of the tool

(image 2). They are submerged steadily.

enough for the operatorto handle the parts.

on the other hand, air bubbles can form if

There are many vivid colours available

the dipping speed is too fast. Prototyping Is essential to calculate the optimum dip

matt or foam-like finishes. PVC is also

speed and tool temperature.

available in clear, metallic, fluorescent

and parts can be produced with gloss,

and translucent grades.

DESIGN OPPORTUNITIES A major advantage is that tooling for

DESIGN CONSIDERATIONS

this process is very low cost. There is no

This process is only suitable for molding

pressure applied to the tool and wear

over a single tool, therefore the accuracy

is minimal with flexible materials,

of the outside details is difficult to

PVC Is the most suitable material for the

so the same tooling can be used for

maintain.The PVC will smooth over

prototyping and actual production. Multiple tools can be mounted together

features such as sharp corners.This will

dip process and so makes up the majority of dip molded and coated products. The environmental credibility of PVC

ENVIRONMENTAL IMPACTS

produce variable wall thicknesses, which

for simultaneous dipping to reduce cycle

can be a problem with protruding details

has been under Investigation In recent

time considerably.Typically, the tooling

because sufficient material may not

years due to dioxins, harmful organic

is machined or cast aluminium, and It 1s

build over them.

a male tool, which Is simpler to machine

Tool design is affected by the nature of the liquid material. Plastisol PVC is

compounds that are given off during both the production andthe incineration

than a cavity.

Wall thickness Is determined by 2

viscous and gels on contact with hot

the liquid polymer. It is also advised that radii are used to help the flow of plastic.

There are many additives, which are used to Improve the material's

in dip molding because the reaction

resistance, UV stability and temperature

process is i-way. It can be ground up and

avoid air bubbles in molten metal. This

resistance, and to reduce its toxicity

used In other applications.

means that sand casting is suitable for

for food-approved grades. The level of

metal. Therefore, flat surfaces, un dercuts

the dip time (dwell). Within reason, high

and holes become air traps if they are not

This is similar to sand casting (page 120), which requires draft angles and fillets to

temperatures and long dips produce thick wall sections. Wall thickness is

designed carefully. Air traps will stop the material coming Into contact with the

generally between 1 mm and 5 mm

hot metal tool, resulting in depressions and even holes where the material has

the production of the tooling because if it can be sand cast effectively then

plastlcizer affects the hardness of PVC.

(0.04-0.2 In.).

not gelled sufficiently. In contrast, air

chances are it will dip mold just as well.

to 100; whereby 30 is very soft and 100 is

include dual colour and different

traps might be deliberately designed into a tool to produce holes that would

COMPATIBLE MATERIALS

shore hardness. As well as the obvious

otherwise need to be punched as a

PVC is the most common material used

COSTS

aesthetic advantages, twin dip can

secondary operation.

for dip molding and coating. Other

Tooling costs are minimal. Cycle time is

To avoid air traps, a draft angle of

materials, in eluding nylon, silicone, latex

rapid and multiple tools reduce cycle

electrical insulation that wears to

between 5° and 15° is recommended on

and urethane, are also used, but only for

time dramatically.

highlight material thinning.

faces that are parallel to the surface of

specialist applications.

It is possible to dip twice to build

provide functional benefits, such as

Gelled material cannot be reused

flame retardant qualities, chemical

factors: the temperature of the tool and

up 2 layers of material.The advantages

of the material.

It Is available from shore hardness A 30 semi-rigid.

Labour costs are moderate.

Featured Manufacturer Cove Industries www.cove-industries.co.uk

Forming Technology

Panel Beating Smooth curves and undulating shapes in sheet metal can be produced with this sheet forming process. Combined with metal

INTRODUCTION Panel beating is controlled stretching

Manual panel beating is a highly skilled process. Coventry Prototype Panels

and compressing of sheet metal. Many

operate a 5-year apprenticeship, which

welding technologies, panel beating by a skilled operator is

techniques are used, including press

is required to learn all of the necessary

braking (page 148), dishing, crimping, wheel forming (English wheeling) and

skills. Wheeling and jig chasing are

capable of producing almost any shape.

jig chasing (hammerforming).These

both smooth and sharp multi-directional

processes in conjunction with arc

curves, embosses, beads andflanges.

1 Low to moderate tooling costs 1 Moderate to high unit costs

Quality High quality handmade

Typical Applications

Suitability

welding (page 288) produce almost any

• Aerospace • Automotive • Furniture

• One-off to low volume production

profile in sheet metal. Panel beating is

Related Processes Deep drawing Stamping Superforming

Speed • Long cycle time, dependent on the size and complexity of part

combined to form sheet materials into

TYPICAL APPLICATIONS

used in the automotive, aerospace and

Panel beating is used in prototyping,

furniture industries for prototyping, pre-

production and repair work for the

production and low volume production

automotive,furniture and aerospace

runs. It is used to produce the entire

industries. Examples of cars that are

chassis and bodywork of cars.

manufactured in this way include Spyker, Rolls Royce, Bentley, Austin Martin and

Above Dishing into a sand bag is now largely confined to prototyping.

CD

Right This Austin Healey 3000 was given a completely new body by Coventry Prototype Panels.

Jaguar. Designers Ron Arad and Ross Lovegrove harness the opportunities of these techniques to produce seamless

Surfaces are planished and polished (page 388) and a skilled operator can

A range of sheet materials can be formed, including stainless steel,

achieve a superior A-class'finish.These

aluminium and magnesium. Even

techniques are used to finish stainless

though magnesium is more expensive

RELATED PROCESSES

steel brightwork for Bentley production

than aluminium, it has superior strength

Stamping (page 82), deep drawing (page 88) and superforming (page 92) are

cars because the requirements of the

to weight and is approximately one-third

surface finish are so high.

lighter.

difference is that panel beating is labour

DESIGN OPPORTUNITIES

production, panel beating is used in

intensive and thus has higher unit costs.

The most important benefit for designers

combination with superforming.These

metal furniture, interiors and sculpture.

For low to medium volume

used to produce similar geometries. The

Stamping and deep drawing require

is that almost any shape can be produced

processes complement each other

matched tooling, which means very

in metal by panel beating. Large and

because superforming produces sheet

high investment costs but dramatically

small radius curves are produced with

profiles with a high surface finish in a

reduced unit costs and improved cycle

similar ease by a skilled operator. Sheets

single operation. Panel beating is used to

time.Therefore, panel beating is usually

can be embossed, beaded or flanged to

produce details such as fins, air intakes

reserved for production volumes of under

improve their rigidity without increasing

and beading that have re-entrant angles

1 o parts per year. Any m ore th an thi s an d

their weight.

and are not suitable for superforming in

it becomes more economical to invest in matched tooling or superforming.

Parts are not limited to the size of the

a single operation.

sheet metal because multiple forms can be seamlessly welded together. In fact,

DESIGN CONSIDERATIONS

QUALITY

most shapes are produced from multiple

A significant consideration is cost. A

Shaped metal profiles use the ductility

panels because they would be too

great deal of skill is required to produce

and strength of metals to produce

impractical to make from a single piece

accurate profiles with a high surface

lightweight and high strength parts.

of material.

finish.This means high labour costs.

Panel Beating Process

Epoxy or steel jig

Dishing into a sandbag

Jig chasing

It also means that there are very few

COSTS

facilities that can carry out such work.

Tooling costs are low to moderate

the level of skill required is very high.

Soft tooling (epoxy) is only suitable for production of up to 10 parts. After this

depending on the size and complexity.

Therefore, labour costs are high, but,

For one-offs and low volumes they

combined with low tooling, costs are

hard tooling in steel is required because

are 5-axis CNC machined (page 186)

considerably cheaper than start-up costs

the soft tooling will continuously have to be replaced. Material thickness is limited

from blocks of epoxy and can be used

for the related processes.

to 0.8 mm to 6 mm (0.024-0.236 in.)

tools are machined from steel, which is

for aluminium and 0.8 mm to 3 mm

considerably more expensive but still a

Panel beating is an efficient use of

(0.024- o.n8 in.) for steel.

great deal less expensive than tooling for

materials and energy.There is no scrap

stamping or superforming.

produced in the forming operations,

COMPATIBLE MATERIALS

Wheel

for up to 10 parts. For higher volumes

Cycle time is long but depends on

Planishing

can be shaped in this way. Aluminium,

is possible to construct the chassis and

bodywork of a car from 3D CAD drawings

operations.

most commonly used sheet materials.

in approximately 6 weeks.

Panel beating the Spyker C8 Spyder ofthe Spyker C8 Spyder in aluminium (image 1), In 1914 Spyker cars merged with the Dutch Aircraft Factory to combine

TECHNICAL DESCRIPTION

their skills in automotives, aircraft and Planishing is a finishing operation and

Panel beating is made up of different

epoxy, or 'hard' and made of steel. Epoxy

operations, such as dishing, jig chasing and

tools will typically only produce up to 10

is essentially smoothing over the surface

been producing lightweight and high

wheel forming. Planishing is used to produce

parts or so before the edge details are

with repeated and overlapping hammer

performance cars.They are manufactured

a smooth finish on panel beaten sheet metal.

too worn. Large circumference curves are

blows. Aflat-faced planishing hammer

in low volumes and so can be modified

typically formed by another method prior

or slap hammer are used to hammer the

to bespoke customer requirements. It is

for certain applications. They are useful

to jig chasing. For example, a sheet may be

surface gently against a dolly or dome. The

even possible for customers to watch cars

in the forming of deep profiles such as

wheel formed to the general shape of the

process stretches the metal slightly but is

being built by the skilled operators via a

motorcycle mudguards. Dishing is rapid,

tool and then jig chased to form accurate

not considered a forming operation. After

dedicated webcam in the factory.

but it is the least accurate and controllable

sheet metal shapes. An engineer's hammer

a succession of taps with the hammer, the

of the panel beating techniques. A wooden,

is used to beat a plastic or metal chaser

operator abrades the surface with a metal

handcrafted aluminium. Sheet

leather or plastic mallet (generally shaped

against the surface of the metal. Plastic

file to highlight remaining undulations. This

aluminium is cut to size (Image 2).

like a teardrop) is used to beat the metal

chasers are used for soft profiles and dish

process is repeated until the desired surface

A crimping machine is used to compress

into shape. With each blow the sand or metal

shapes, while metal chasers are used for

finish is required. After this the metal work

(gather) the metal together in a selected

shot displaces and conforms to the shape

tight bends, sharp angles and flat surfaces.

is sanded and polished.

area for increased curvature on the wheel

Bags of sand or metal shot are still used

of the profile of the hammer, which allows

Wheel forming is also known as English

the metal to be formed. It requires a great

Wheeling. It was developed and mastered by

deal of skill to stretch and compress the

panel beaters in early automotive production

metal accurately Into the bag. Hammering

in England. The metal workpiece is passed

into a shaped dolly or over a stake is more

back and forth between a wheel and an anvil.

accurate but less versatile.

The wheel is flat faced and the anvil has a

Jig chasing (also known as hammerformingl is the process of stretching

profile (crown). The role of the anvil is to stretch the sheet progressively with each

and compressing Igatheringl sheet metal

overlapping pass. Low-crown anvils produce

to conform to the shape of a CNC machined

a large radius curve and high-crown anvils

tool. The tool is either 'soft' and made of

produce a tighter bend.

although there may be scrap produced

magnesium and all types of steel are the

the size and complexity of the part. It

This case study illustrates the production Wheel forming

ENVIRONMENTAL IMPACTS

in the preparation (ofthe blank,for instance) and subsequent finishing

Most ferrous and non-ferrous metals

Case Study Preformed metal workpiece

This is a labour intensive process and

aerodynamics. Since then they have

The chassis and bodywork are

former (image 3). It works like 2 pairs of pliers, gripping and forcing the sheet together in tandem.

r other side of the metal by the operator

The wheel former is made up of a flat-

(image 12). It takes a great deal of skill and

faced wheel and a low- or high-crowned

anvil (image 4). The sheet is passed bacl< and

patience to achieve the desired finish.

forth between the rolls in overlapping strokes

The finished panels are polished to a very

(image 5). Each pass stretches the metal

smooth finish and spray painted. In the

slightly and so forms a 2-directional bow in

meantime, the brightwork is polished on

the sheet.

conventional polishing wheels (image 13).

When the correct curvature is

Assembly of the car engine, suspension

approximately achieved in the sheet, it is

and interior (images 14 and 15) is carried out

transferred onto the jig chaser. It is clamped

by Karmann in Germany.

onto the surface of the epoxy tool and gradually stretched and compressed to conform to the shape (image 6).The sheet is worked gently with a variety of chasers until it matches the shape of the epoxy tool precisely. Polyamide (PA) nylon chasers are used to stretch selected areas of the

sheet into embossed details (image 7). Aluminium chasers are used to form flat

>

areas (image 8).

The sheet is removed from the tool CD

m >

and holes are cut and filed (image 9). After this it is mounted onto the tool once again and reworked with an aluminium

chaser (image 10). The panels are shaped individually and then brought together on a jig. They are TIG welded (page 290) to form strong and seamless joints (image 11). Each weld is carefully levelled by grinding, planishing, filing and polishing. A slap hammer is used to planish the curved metal onto a dolly, which is held on the

7

Featured Manufacturer Coventry Prototype Panels 6

8

www.covproto.com

TECHNICAL DESCRIPTION

Spinning Process

In stage 1 of the spinning process, a

circular metal blank is loaded onto the tool (mandrel). In stage 2, the metal blank and mandrel are spun on the lathe and a rolling wheel forces the metal sheet onto

Forming Technology

Metal Spinning

the surface of the mandrel. This stage of

the process is similar to throwing clay on a potter's wheel. The metal is gradually

Spinning is the process of forming rotationally symmetrical sheet metal profiles. It is carried out on a single-sided tool, as progressive tooling or - in a process known as spinning on-air'

- without tooling at all.

shaped and thinned as it is pressed onto

INTRODUCTION

the mandrel. In this case the finished part

Although metal spinning is an industrial

cannot be removed from the mandrel until it

process, it has retained elements of

is trimmed. In stage 3, the mandrel is split

craft. The combination of these qualities

so that a re-entrant angle can be shaped

makes this a very satisfying process with

in the neck of the part. The top and bottom

which to work.

are trimmed and the part is demolded. The

Metal spinning can be utilized to form sheet profiles including cylinders,

whole process takes less than a minute.

Costs

Typical Applications

Suitability

cones and hemispheres. It is frequently

• Low tooling costs • Moderate unit costs

• Automotive and aerospace • Jewelry • Lighting and furniture

• One-offs and low to medium volume production

combined with punching, fabrication

Quality 1 • Variable: surface finish is largely dependent on the skill of the operator and the speed of the process

Related Processes

Speed

• Deep drawing • Metal stamping

• Moderate to rapid cycle time, depending on part size and complexity, and the type and thickness of material

DESIGN OPPORTUNITIES

or pressing to provide a wider range

Metal spinning is an adaptable process.

of design opportunities such as

Tooling for manually operated low

flanged edges, asymmetric profiles and

production runs is relatively inexpensive. This means that designers can realize

perforated shapes.

their ideas with this process early on and make structural and aesthetic adjustments to the 3D form. Ribs, undulations and surface texture can

be integrated into a single spinning operation. Steps or ribs can reduce wall thickness and so produce thinner and more cost-effective parts. Textures can be integrated onto only

1 side of the part because a low profile texture on the mold will not be visible on the opposite surface. Metal spinning

TYPICAL APPLICATIONS

of shapes and technical features. Simple

can also form meshes and perforated

This process is utilized in the furniture,

profiles can be extruded or fabricated

sheet materials.

lighting, kitchenware, automotive,

and time scales, quantities andbudget

aerospace and jewelry Industries. Some

determine the appropriate choice.

The tool (mandrel) can be male or female depending on the part geometry. In both cases only 1 tool is required, unlike

typical products made in this way include anglepoise lampshades, lamp

QUALITY

matched tooling used in deep drawing

stands, flanged caps and covers, clock

A very high finish is achievable by skilled

and stamping.Therefore, changes are

operators with manual and automated

relatively inexpensive and the tooling

processes.The quality of the inside

costs are considerably reduced.

facades, bowls and dishes.

RELATED PROCESSES Metal stamping (page 82) and deep drawing (page 88) are capable of

surface finish is determined by the mold and the outside surface finish is shaped

DESIGN CONSIDERATIONS

by the tool. Manual and automated

Metal spinning is limited to rotationally

producing similar profiles in sheet metal.

techniques are often combined for

symmetrical parts. The ideal shape for

Metal spinning is often combined with

optimum quality. There is no tooling for

this process is a hemisphere, where the

pressing and metal fabrication to achieve

spinning on-air and the inside surface

diameter is greater than or equal to

more complex geometries, a wider range

finish is therefore not affected.

twice the depth. Parts that have a greater

Case Study

Spinning the Grito lampshade A combination of automated and manual

determined by the design of the part. In

techniques is used to shape the Grito

this case manual metal spinning is required

lampshade. The metal blank is cut and

to achieve a re-entrant angle on the neck

loaded onto the mandrel (image i) and the

of the lampshade. This is made possible by

CNC metal rolling wheel guides the blank

splitting the mandrel inside the part so that

over the surface of the mandrel in stages

each piece can be removed independently.

(image 2). With each pass the metal sheet

The shape is worked by the craftsman,

is manipulated and controlled in much

who gradually improves the surface finish

the same way as clay throwing (page 172).

with a polished profiled metal tool (image

The metal can be drawn out and thinned,

7). Once spinning is complete, the surface

or simply pressed onto the surface of the

finish is improved further by polishing with

spinning mandrel. It takes only 30 seconds

an abrasive pad (image 8). The top and

to complete the first stage of the spinning

bottom are trimmed and the 2 parts of the

process (image 3).

mandrel removed. Post-spinning operations

The parts are made in batches, which

include punching in 2 stages (image 9) and

are stacked up in preparation for the next

painting. The parts are masked (image 10)

stage of spinning (image 4). The pre-spun

and then sprayed (image 11). The finished

parts are now loaded onto a manually

part (image 12) is slipped over the cord and

operated spinning lathe and worked by

bulb and is supported by the undercut in

hand (image 5). This requires a profiled

the neck.

tool (image 6), the shape of the too! being

depth than diameter are achievable but

runs. Materials include wood, plastic,

will greatly increase costs. Parallel sides

aluminium and steel. For large

and re-entrant angles are also possible.

production runs the metal tooling costs

However, this can entail multiple

are considerably cheaper than for metal

interlocking tools and will increase cost.

stamping and deep drawing because

Work hardening in steels Is another

metal spinning uses a single-sided tool.

consideration for a designer,This factor

Spinning on-air needs no tooling, but the

can prove advantageous: for example,

labour costs tend to be higher.

work hardening can increase the durability of a part. However, parts that

Cycle time is determined by the size and complexity of the part and the

need to be worked on after spinning have

choice of material. Forming aluminium

to be stress-relieved by heat treatment

is far quicker than steel because of its

processes, which is a disadvantage.

ductility and malleability. Steel may also

Small to very large parts can be metal spun up to 2.5 m (8 ft) in diameter and tolerances down to 1.5 mm (0.059 in.).

require heat treatment, which further increases cycle time. Labour costs can be moderate to high for manual operations, especially if a

COMPATIBLE MATERIALS

very high quality, A-class aesthetic finish

sheet is cut into a circle. However, waste

Mild steel, stainless steel, brass, copper,

is required. Automation reduces labour

metal is readily recycled. In operation, a

aluminium and titanium can all be

costs considerably.

small amount of metal is trimmed from the part, in order to finish the edges.

formed by metal spinning,

ENVIRONMENTAL IMPACTS

Energy requirements for this process

COSTS

The metal blank is often supplied as a

are quite low, especially if it is manually

Tooling costs can be very low, especially

square sheet, so there is waste produced

operated. The energy used is equivalent

for prototyping and low production

at the beginning of each cycle when the

to turning a lathe.

Featured Company Mathmos www,ma[hmos.co.uk

Metal Stamping Process

This cold metal pressing technique is used to form shallow sheet

sheet materials. Round, square and

polygonal shapes can be made with

and bend profiles in sheet metal. It is rapid and precise, and is

similar ease.

used to produce a wide range of everyday products from car

Ribs can be integrated into parts to reduce the required wall thickness.This

bodies to metal trays.

has a knock on effect in reducing weight and cost.

Shapes with compound curves and

TECHNICAL DESCRIPTION

Costs

Typical Applications

Suitability

complex undulating profiles can be

Metal stamping is carried out on a

• High tooling costs • Low to moderate unit costs

• Automotive • Consumer products • Furniture

• High volume production

formed between matched tools.The

punch press. The power is transferred

up to eject the part, which Is removed.

only other practical way of forming

to the punch by either hydraulic rams or

Sometimes the part is formed in a

these profiles is by panel beating, which is labour intensive and a highly skilled

mechanical means such as a flypress.

continuous strip, out of which it then

Hydraulic rams are generally preferred

has to be punched. This is common in

process. Soft tooling can be used to

because they supply even pressure

progressive die forming.

progress from panel beating to metal

throughout the stamping cycle. Even so,

Quality • High quality and precise bends as a result of matched tooling

Related Processes • Deep drawing • Metal spinning • Press braking

Speed • Rapid cycle time (under 1 second to 1 minute)

stamping.This is where 1 side of the tooling is made of semi-rigid rubber,

INTRODUCTION

TYPICAL APPLICATIONS

have to be drawn out and their wall

Metal stamping is used to describe forming shallow metal profiles between

Stamping is widely used. Most mass

thickness reduced.This has to be carried

matched steel tools.Tooling costs are

high and so this process is only suitable for high volume production.

production metalwork in the automotive industry is stamped or pressed. Examples include bodywork, door linings and trim. Metal camera bodies, mobile phones,

which applies enough pressure to form the metal blank over the punch.

out gradually and more slowly to avoid overstretching and tearing the material.

DESIGN CONSIDERATIONS

Superforming (page 92) can produce large and deep parts in a single

Stamping is carried out on a vertical to be formed with a secondary pressing

axis.Therefore, re-entrant angles have

flypresses still have their place in the metalworklng industry.

The punch and die (matched toolingl

After forming, the stripper rises

In progressive die forming the stamped metal workpiece would now be transferred to the next workstation. This is either carried out manually,

are dedicated and generally carry out

or by a transfer yoke. Most systems

a single operation such as forming or

are automated for very high-speed

punching. In operation, the metal blank

production. The next operation may be

is loaded onto the stripper. The punch

further pressing, punching, beading or

then clamps and forms the part in a

another secondary operation.

single stroke.

television housing, appliances and MP3

operation. However, it is limited to

precise shapes without significantly

players are formed by stamping. Kitchen

aluminium, magnesium and titanium

operation. Secondary operations include

reducing the material's thickness. It is

and office equipment, tools and cutlery

because they are the only materials with

further press forming, cutting, deburring

known as deep drawing (page 88) when the relationship between depth and

are made in this way. Not only are the

suitable superplastic properties.

and edge rolling.

0.4 mm and 2 mm (0.02-0.08 in.). It is

a single-sided steel tool and is only

external features stamped, but also much of the internal metalwork and

QUALITY

possible to stamp thicker sheet, up to 6 mm (0.236 in.), but this will affect the

capable of low volume production.

diameter mean that controlled drawing

The first stamping operation can only reduce the diameter of the blank by up to

is required, which slightly reduces the

structure is shaped in the same way.

Shaped metal profiles combine the

30%. Subsequent operations can reduce

shape that can be formed.

to ovenoo parts per minute. Changeover

ductility and strength of metals in parts

the diameter by 20%. This indicates the

with improved rigidity and lightness.

number or operations (workstations)

COMPATIBLE MATERIALS

required in the production of apart.

Most sheet metals can be formed in this

because this process is mechanized

way including carbon steel, stainless

It is a rapid process used to form

material's thickness during forming. Mass produced parts that require

RELATED PROCESSES

Cycle time is rapid and ranges from 1 and setup can be time consuming. Labour costs are generally low

multiple forming and cutting operations

Low volume parts are manufactured by

are produced with progressive dies,

panel beating (page 72) metal spinning

simply deburred after forming. Polishing

a process made up of a series of dies

(page 78) or press braking (page 148).

(page 388) is used to improved surface

this process are often determined by

steel, aluminium, magnesium, titanium,

and often fully automated. Finishing products by polishing will increase

working very rapidly and in tandem.

These can produce similar geometries

finish. Parts can also be powder coated

the capabilities of the machine; bed

copper, brass and zinc.

labour costs considerably.

While a part is being formed the

to metal stamping, but they are labour

size determines the size of blank and

second operation is being carried out

intensive and require skilled operators.

(page 356), spray painted (page 350) or electroplated (page 364).

stroke determines the length of draw

COSTS

ENVIRONMENTAL IMPACTS

simultaneously on the part that was

Even though stamping and deep

achievable. Speed is determined by stroke

Tooling costs are high because tools have

All scrap can be recycled. Metal stamping

to be machined precisely from high-

produces long lasting and durable items.

tooling is less expensive, but still requires

If appearance is not critical, parts are

As in deep drawing, the limits of

formed previously and so on. Parts may

drawing are similar, there are distinct

DESIGN OPPORTUNITIES

require 5 operations or more, which is

differences between them. Parts with a

These are rapid and precise methods

height andthe complexity of the part. The thickness of stainless steel that

reflected in the number of workstations.

depth greater than half their diameter

forforming shallow metal profiles from

can be stamped is generally between

strength tool steel. Semi-rigid rubber

Case Study

Blank preparation There are 2 main processes used to cut

s

out the blanks for metal pressing.The first is punching.The tooling is expensive and so it is limited to parts that are produced in high volumes and are relatively simple shapes (images 1 and 2). This example is the Cactus! bowl, made by stamping and punching. It was designed by Marta Sansoni and production began in 2002,

The alternative is to laser cut the parts. This can produce very complex blanks and thus reduce secondary operations

(images 3 and 4). The Mediterraneo bowl illustrated here was designed by Emma Silvestris in 2005.

Featured Manufacturer

Alessi www.alessi.com

Case Study

Metal stamping Stamping is used across many industries and

onto a spinning clamp, a rolling cutter is

for a wide range of applications. Alessi is an

introduced from the side and the excess is

example of a manufacturer who uses metal

trimmed (image 8). The formed parts are

pressing (stamping and deep drawing) to

stacked up in preparation for secondary

produce parts of the highest standard. The example that is used to demonstrate

operations (image 9). In this case, a small

bead of wire is rolled into the perimeter

the stamping process is a serving plate,

of the tray to give it rigidity. This helps to

which is formed in stainless steel sheet. It

reduce the gauge of metal used.

was designed by Jasper Morrison in 2000 (image 1). The metal blanks are laser cut in batches.

They are coated with a thin film of oil just prior to stamping (image 2). This is essential to ensure that the metal will slide between the die and punch during operation. The blank is loaded onto the tool and stamped (images 3-6). It is a rapid process and each part takes only a few seconds to complete. The part is removed from

Featured Manufacturer

the stripper (image 7). It is transferred

Alessi www.alessi.com

T

TECHNICAL DESCRIPTION

Secondary Pressing Processes

Case Study

Secondary pressing covers a range of processes, including further stamping,

Secondary pressing operations

bending, rolling, beading or embossing. Side action tools are used to create re-entrant angles that are not possible in a single operation.

page 263. If this product was manufactured

the edge ofthe plate; without a roll it would

secondary pressing and deburring operations.

in very large volumes, these processes would

feel very thin and would damage easily.

The first example is a product from the

Exchanging the punch for a roller die and spinning the part makes it possible to apply

These images demonstrate some typical

Kalisto family, designed by Clare Brass in 1992

Metal platform

(image 1). First of all the metal is deep drawn.

Side action

a bead, rolled edge or other detail that runs continuously around the product.

Stripper

Stage 2: Press

Stage 3; Strip

progressive die forming.

The stamped plate is placed onto a

Then it is placed onto separate tooling that

spinning clamp (image 5). There is a sequence

applies sideways pressure (image 2). The parts

of 3 operations, which include cutting (see

are spun against the side ofthe tool, forming

image 8, page 85), deburring (image 6) and

the side profile (image 3).

then edge rolling (image 7).

The second example is the Tralcio Muto Stage 1: Load

be combined into adjacent workstations as

The rolled edge increases the stiffness of

tray (image 4), which was designed for Alessi

the part and means thinner gauge steel can

by Marta Sansoni in 2000. It is punched on

be used (image 8). It also improves the feel of

¦¦

geometries. Simple cup-like geometries

i Hollow

Forming Technology

Deep Drawing

(which is restricted by stroke height and complexity of part).

can be produced in a single operation,

Surface finish is generally very good, but

while very deep parts and complex

depends on the quality of the punch and

geometries are made using progressive

die. Wrinkling and surface issues usually

dies or the reverse drawing technique.

occur around the edge, which is trimmed

Deep drawing relies on a combination of

Reverse drawing presses the sheet

post-forming.

a metal's malleability and resistance to

that forces a sheet metal blank into a closely matched die to produce sheet geometries. Very deep parts can be formed using progressive dies.

Typical Applications

Suitability

• Automotive and aerospace • Food and beverage packaging • Furniture and lighting

• Medium to high volume production

inverting the shape after the first draw.

DESIGN OPPORTUNITIES

Operating in this way accelerates

Various sheet geometries can be

cycle time and reduces the number

produced with the deep drawing,

Cold metal pressing is known as 'deep

of progressive tools required.

including cylindrical, box-shaped and

TECHNICAL DESCRIPTION

irregular profiles, which can be formed

The deep drawing process is carried

drawi n g' wh en th e depth of th e draw i s greater then the diameter (sometimes

TYPICAL APPLICATIONS

when the depth is only 0.5 times greater

The most common products

than the diameter).This process can

manufactured by deep drawing include

progressive dies or perpendicular action

be used to produce seamless sheet

beverage cans and kitchen sinks.

in the drawing press. However, this will

geometries without the need for any

However, these techniques are also

greatly increase the tooling costs.

further forming or joining operations.

used to produce a variety of items in

There is a limit to how much sheet

with straight, tapered or curved sides.

the automotive, aerospace, packaging,

DESIGN CONSIDERATIONS

furniture andlighting industries.

Depending on the type of material

Speed

• Good surface finish

• Metal spinning • Metal stamping • Superforming

• Rapid cycle time (a few seconds to several minutes), depending on the number of operations

out in different ways - the method

of process being determined by the

Undercuts can be achieved with

andthe type of material and sheet Related Processes

steels, zinc, copper and aluminium alloys.

INTRODUCTION

metal can be deformed in 1 operation,

Quality

COMPATIBLE MATERIALS

thinning.The most suitable materials are

material twice in a single operation,

In this cold metal forming process, the part is made by a punch

1 High to very high tooling cost 1 Moderate unit cost

QUALITY

complexity of the shape, depth of draw, material and thickness. In stage 1, a

sheet metal blank is loaded into the hydraulic press and clamped into the blank holder. In stage 2, as the blank holder progresses downwards the material flows over the sides of the

and thickness, parts ranging from less

lower die to form a symmetrical cup

thickness determine the level of

RELATED PROCESSES

than 5 mm to 500 mm (0.2-19.69 in.)

shape. In stage 3, the punch forces the

deformation. A variety of techniques

Shallow profiles are formed by metal

in diameter can be formed by deep

material through the lower die in the

are therefore used to produce different

stamping (page 82). Metal spinning (page 78), sheet ring rolling (see tube

drawing.The length of draw can be

opposite direction. The metal flows

up to 5 times the diameter of the part.

over the edge of the lower die to take

and section bending, page 98) and

Longer profiles require thicker materials

the shape of the punch. In stage U, the

superforming (page 92) can be used

because material thickness is reduced in

part is ejected.

to make similar geometries in sheet

long draws.

metal. Deep drawing and metal spinning

produce seamless parts that typically do

The tonnage of the press is

The limits of deep drawing are often

determined by the capabilities of the machine such as bed size (controls the

need to be welded post-forming.

determined by the tooling. Anything up to 1,000 tonnes may be applied to shape a long or large profile.

size of blank), stroke (determines the length of draw achievable) and speed

Deep Drawing Process Punch

Metal blank

Profile of first draw

Blank holder

Lower die

4 Stage 1: Load

Stage 2: Draw

Stage 3: Reverse draw

Stage 4: Finished part

r

Case Study

Deep drawing the Cribbio Blanks are cut to suit each deep drawing

metal to flow over the lower die (image 4).

(image 7). At this point the metal blank has

application. In this case, the Cribbio is circular,

The punch simultaneously forces the material

been forced through 2 progressive deep

so a circular blank is cut from a sheet of 0.8

inside the lower die (turning it inside out).

drawing cycles, which both applied reverse

mm (0.031 in.) carbon steel (image 1). The final

The first stage of this part's forming is

draw. Even though the Cribbio is a complex

part has a reduced wall thickness of 0.7 mm

complete and it is removed (image 5).

part to deep draw, production remains as

(0.028 in.) as a result of thinning during

The drawn part is loaded onto the second

high as 50 parts per hour. The top edge is then

drawing. A fine layer of oil is then applied

of the progressive dies (image 6). A punch

trimmed to remove any wrinkles and tearing

to both sides of the blank, forlubrication

forces the material into the lower die, turning

that may have occurred to the perimeter

(image 2).

it inside out once again.This process of

of the metal blank during clamping and

reverse deep drawing means that fewer

drawing (image 8) and so produce a clean

(image 3) on a 500 tonne press, which

tools are required to achieve the same length

edge detail. The parts are transferred onto a

progresses downwards, forcing the sheet

of draw. The drawn part is then removed

punch that perforates the surface (image 9).

The blank is loaded into the blank holder

Side actions are extremely expensive

to incorporate into the deep drawing cycle, so are often carried out postforming. After perforation a ring of

pressed metal is crimped over the top edge to create a safe and ergonomic

trim (images 10 and 11).The steel Cribbio is finished with a hardwearing epoxy

i

coating (image 12). 5

4

Metals with high resistance to thinning

to precise tolerances. Progressive

ENVIRONMENTAL IMPACTS

are less likely to tear, wrinkle or fracture

tooling, required to produce complex

Scrap is produced when the sheet

during processing, so thinner sheet

or especially deep parts, increases costs

material is cut to size and the finished

material can be used to start with,

considerably for this process.

part trimmed. Fortunately, all scrap

Cycle time is quite rapid but depends

COSTS

on the number of stages in the pressing

Tooling costs are very expensive because

cycle, while labour costs are moderate

the punch and die have to be engineered

due to th e 1 evel of autom ati on.

material can be recycled into new sheet Featured Manufacturer

metals or other metal products. Rexite www.rexite.il

Lett Tests show that a piece of superplastic aluminium alloy will stretch several times its length without breaking.

superplastic alloys such as 2014,2024, 2219 and 6061, making the process ideal for producing structural components.

Finite element analysis (FEA) flow simulation software helps to reduce the

Forming Technology

time needed to get from CAD design to

Superforming

superformed product.

TYPICAL APPLICATIONS This recently developed hot forming process is used to produce sheet metal parts following similar principles to thermoforming: a metal blank is heated to softening point and formed onto a single-sided tool using air pressure.

INTRODUCTION

The use of these processes to create

Superform alummium developed the

complex sheet geometries from a single

technique of superforming aluminium

piece of material has been rapidly

alloys and more recently magnesium

growing in many applications, including

alloys. The process was developed to

aerospace, automotive, buildings, trains,

reduce the weight of metal components

electronics,furniture and sculpture.

aerospace designers are beginning to

Superforming of 5083 is performed using the cavity or bubble forming technique.

RELATED PROCESSES

see the benefits that the superforming

A heat treatable alloy processed to

Metal stamping (page 82) and deep drawing (page 88) are used to make

of such alloys brings to the design and

give excellent superplasticforming

manufacture process. For example, they

properties-with component strains in

similar sheet metal geometries, while

eliminate costly fabrication work by

excess of 200%-is 2004, which allows

thermoforming (page 30) and composite laminating (page 206) produce similar

forming large parts from a single sheet,

complex detail to be achieved.Typical

thereby enhancing structural integrity

uses include electronic enclosures,

onto a single surface male or female

geometries in thermoplastics and glass

while reducing costs and improving

aerospace components and smaller

tool using air pressure. There are 4 main

reinforced plastic (GRP) composites.

repeatability.

complex form components. Unprotected

by minimizing fabrication operations and required wall thickness. Typical Applications

Suitability

• Aerospace • Automotive • Furniture

• Low to medium volume production

Quality

Related Processes

Speed

• Very good surface finish

• Deep drawing • Metal stamping • Thermoforming

• Rapid cycle time (5-20 minutes! • Trimming and assembly operations increase overall processing time

Low to moderate tooling costs Moderate to high unit costs

.

Superforming is a hot metal forming process that uses similar principles

to thermoforming plastics (page 30). A sheet of aluminium is heated to 450-5000C (840-9320F) and then forced

types of superforming: cavity, bubble,

successfully shaping such materials, and

Another advantage of the

2004has similar corrosion resistance

backpressure and diaphragm. Each of

QUALITY

superforming process is the range of

these techniques has been developed to

The surface finish on the tool and the

aluminium alloys that can be formed,

alloys. In most service situations it

fulfil specific application requirements.

accuracy of any post-forming operations

providing solutions to virtually any

is necessary to have some form of

affect the quality of a superformed part. Like thermoforming, the side of the sheet

engineering problem.

complex parts such as automotive body

panels and is excellent for shaping 5083

that does not come into contact with the

magnesium and manganese. It is used

enhance the corrosion resistance of these

aluminium alloy.

mold will have the highest quality finish.

for applications requiring a weldable moderate strength alloy having good

give enhanced corrosion resistance.

Cavity forming is good for large and

Bubble forming is suitable for deep

Typically, the aluminium alloys exhibit

The alloy 5083 contains aluminium,

to other copper containing aluminium

surface protection. Cladding with pure aluminium is commonly used to

alloys with Clad 2004 being designed to The alloy 7475 contains aluminium,

complex components, especially where

good corrosion resistance, mechanical

corrosion resistance. As such it is an

wall thickness needs to remain relatively

strength and surface finish.The alloys

excellent all-round alloy and ideal

constant.This process can be used

that are suitable for superforming have

for many applications. Superformed

suitable for applications requiring the

to manufacture geometries that are

differing characteristics, which make

high strength of 7075 and increased

impossible to achieve using any other

them useful for a variety of applications.

components using 5083 alloy sheet are supplied in the 0 temper and offer many advantages over parts fabricated

DESIGN OPPORTUNITIES

from 1200 or 3000 series and other

is approximately the same as that of 7075 combined with toughness similar

developed to produce structural aircraft

Like other aluminium parts, superformed

5000 series alloys. Simple or complex 3D

to 2024-T3 at room temperature. Its

components in 7475 alloys. Although

components can undergo a range of

sheet geometries can be manufactured

high strength to weight ratio allows

similarto cavityforming,the process

post-forming operations to achieve the

as a single piece forming with high

its extensive use within the aerospace

differs by using air pressure from both sides of the sheet. It is gradually pulled

final desired part or assembly.

quality surface finish, making 5083

industry for structural components.

forming process. The backpressure forming process was

The diaphragm forming process can

zinc, magnesium and copper. It is

fracture toughness.The sheet's strength

particularly suitable for automotive, rail,

Resistance to stress corrosion cracking

onto the surface of the tool using slight

be used to form parts that are generally

architectural and marine applications.

and exfoliation are similar to that of

pressure differential.This maintains the

classified as 'non-superplastic'.This

This alloy allows a good compromise

7075.The T76 type temper provides for

integrity of the sheet and means that

allows alloys used for aircraft structures,

between formability and corrosion

improved exfoliation resistance over

'difficult' alloys can be formed.

such as 2014,2024,2219 and 6o5i,to be

resistance, combined with moderate

T6 type temper, with some decrease in

superformed. In many cases diaphragm

strength.Typical applications of 5083

strength. Stress corrosion cracking in

forming is the only practical way of

include transportation and construction.

7475 T76 is not anticipated if the total

Diaphragm forming is used to shape complex sheet geometries in non-

TECHNICAL DESCRIPTION

Superforming Process

In all U superforming processes a sheet of

Cavity forming

metal is loaded into the machine, clamped in place and heated to between 450°C and

500°C (840-932oF). The temperature is determined by the type and thickness of sheet material. Stage 1; Preheated sheet loaded stage 2; Pressure applied

In cavity forming, the hot metal sheet is forced onto the inside surface of the tool by air pressure at 1-30 bar (U.5-435 psi|. The

Bubble forming

LUl

hot metal is superplastic and so forms easily over complex and intricate shapes. This process is generally used to manufacture

EH]

large shallow parts.

Bubble forming is similar to Stage 2: Vacuum applied

thermoforming. In stage 1, the hot metal

sheet is blown into a bubble and the tool rises into the mold chamber. In stage 2, the Stage 1; Preheated sheet loaded and blown

pressure is then reversed and the bubble of

Backpressure forming

the tool. This process is ideal for deep and

metal is forced onto the outside surface of

complex parts. The wall thickness is uniform because the bubble process stretches the material evenly prior to forming.

D 1} Stage 1: Preheated sheet loaded Stage 2: Pressure applied

Backpressure forming is very similar

to cavity forming. The difference is that in backpressure forming air pressure is also

applied to the reverse side of the hot metal sheet as it is being superformed. In this way

Diaphragm forming

the forming process is more controlled and

allowing unrestrained movement of the

the metal bubble. Only a virtual image of

can be retracted (image 4). The part is now

reduces the stress on the hot metal sheet.

component sheet.

this stage of the process is shown in image

formed and ready for trimming and any

2 because the metal sheet is not usually

other post-forming operations.

Diaphragm forming was developed to

1} ft D Stage 1: Preheated sheet loaded Stage 2: Pressure applied

superform so-called 'non-superplastic'

THE BUBBLE FORMING SEQUENCE

translucent. As the tool rises up the hot

alloys. It can achieve this because the

The bubble forming sequence shows how

metal is forced onto its surface by air

metallic sheet diaphragm supports the

aluminium is superformed. The hot metal

pressure (image 3). The tool continues to

hot metal sheet and aids the flow of

sheet is blown Into a bubble in the molding

rise and the metal is forced onto it until the

material into complex 3D profiles, by

chamber (image 1). The tool rises up into

forming process is complete and the tool

sustained tensile stress is less than 25%

produce parts up to 950 x 650 x 300 mm

Primary structure applications for the

In the formed condition the alloy has

COSTS

of the minimum specified yield strength.

(37 x 26 x 12 in.) and 6 mm (0.236 in.) thick.

aerospace industry require high strength

suitable mechanical properties for

Although tooling costs can be quite low

Backpressure forming has a maximum

alloys accompanied with good service

internal fittings such as kicking panels andlight fittings.

compared to matched die tooling, they do depend on the size and complexity

DESIGN CONSIDERATIONS

plan area of roughly 4,500 mm2 (6.97

properties such as fatigue toughness

The maximum size of part that

in.2), and diaphragm forming can be used

and stress corrosion resistance.These

can be formed is different for each

to produce parts up to 2,800 x 1,600 x

requirements are adequately met

COMPATIBLE MATERIALS

superforming technique. In each case, 1

600 mm (110 x 63x24 in.).

with the alloy 7475, which has been

Superplastic metals that can be shaped

of the limiting dimensions can often be

Different alloys have different

of the part. Cycle time is rapid, typically

successfully used to form air intake

in this manner include aluminium,

exceeded depending on part geometry

mechanical and physical properties, and

lip skins and access door assemblies,

magnesium and titanium alloys.The

and alloy selection.

this must be taken into consideration

for example. For less demanding

most commonly formed aluminium

Cavity forming can be used to produce

5-20 minutes.

Labour costs are moderate. Each part is trimmed and cleaned post-forming.

ENVIRONMENTAL IMPACTS

during the design process. It may well

applications the heat-treated version

sheet materials include 5083,2004

Scrap and offcuts are recycled to produce

parts up to 3,000 x2,000 x600 mm (n8

be possible to form a complex shape in

of 2004 has found many applications

and 7475.

new sheets of aluminium and other

x 79 x 24in.) and 10 mm (0.4in.) thick,

i alloy, but that alloy may not have the

for secondary structures such as

while bubble forming can be used to

properties requiredfor in-service use.

aerodynamicfairings and stiffeners.

aluminium products.

Case Study

Superforming the Siemens Desiro train facade The aluminium sheet is loaded into the superforming mold (image i).The clamps are brought down onto the perimeter of the sheet (image 2) and the temperature increased to 4500C (8400F). The superforming cycle takes approximately 50 minutes, after which the part is unloaded (image 3).The demolded part is loaded onto a support structure and CNC trimmed and machined (image 4),The scale and complexity of the part can vary greatly before it is assembled (image 5). The train front is made in 2 halves so it has to be tungsten inert gas (TIG) welded to form the complete front unit. The 2

oi

c

halves are brought together in a specially

n m

designed jig (image 6) and welded (image

o

7). CAD renderings are available of the Siemens Desiro train facade, which the

panels are destined to become (image 8).

50 Tl

xi

Forming Technology

Tube and Section Bending Used mainly in the furniture, automotive and construction industries, this process is used to form continuous and fluid metal structures. Tight bends can be formed with a mandrel over a rotating die, or long and undulating curves between rollers.

Costs r] • No cost for standard tooling i • Moderate to high cost for specialized tooling • Low to moderate unit costs

INTRODUCTION

Steam bent (page 198) furniture was

Architects and designers have long

the precursor to tubular steel and uses

utilized the functional and aesthetic

similar bending techniques.Tubular

properties of bent metal, especially

steel was developed in Germany for the

tubular steel. Bending methods are

automotive and aerospace industries,

generally inexpensive and make use

andThonet saw its potential. In the 1920s

of the ductility and strength of metal.

they began developing tubular steel

Bending minimizes cutting andjoining

furniture with members of the Bauhaus,

Typical Applications

Suitability

in certain applications, which reduces

including Mart Stam, Marcel Breuer and

profiles with multiple bends on a suitably Above, left

• Construction • Furniture • Transport and automotive

• One-off to high volume production

waste and cost.

Mies van der Rohe. Many of the designs

shaped punch. An example of this is

from this time are still in production.

chairs are commonly

hexagonal lampposts that are tapered

Above Ring rolling can shape tube, extruded profile

produced by mandrel

and metal sheets. The

along their length.

bending.

arc can be adjusted along its length to give

There are 2 main types of tube and section bending, which are mandrel

Quality • High

CD m >

Related Processes • Arc welding • Press braking • Swaging

Speed • Rapid cycle time • Machine setup time can be long

in

bending and ring rolling (see images,

TYPICAL APPLICATIONS

opposite, above).

Metalwork is either bent as a continuous

profiles to roll forging (page 114). The

Mandrel bending is specifically designed for making small radii in metal

length, or fabricated using cast or

difference is that roll forged components

sections. Many products are formed by

is inserted into the metal tube to prevent

mandrel bending, including domestic

it from collapsing during bending. Ring

and office furniture, security fencing

rolling is used to form continuous and

and automotive applications (such as ,

generally larger bends in both tube and

exhaust pipes).

commonly known as section bending.

Ring rolling can produce similar

non-circular bends.

pre-bent 'elbows' to join straight

tube. It is named after the mandrel that

section (extruded profile or bar). It is also

The legs of tables and

Mandrel Bending Process

Ring rolling can be used to bend a range of profiles (tube, extrusions and bar) into large-radius bends. Many products are formed using this technique such as structural beams (for

bridges and buildings), architectural trims (on curved facades) and street

Mandrel Stage 1: Load

Stage 2: 90° bend

furniture. In fact, most bent metalwork in construction will be processed using ring rolling. Rolling sheet materials is known as plate rolling.

It is even possible to produce 3D section bends such as the tracks on a rollercoaster, which can be achieved with careful manipulation on aring roller.

RELATED PROCESSES

TECHNICAL DESCRIPTION The metal blank Itubel Is loaded over

inside of the bend, especially for very thin

the mandrel and clamped onto the die.

walled sections.

Non-mandrel forming Is only possible for certain parts with thicker walls.

The blank Is drawn onto the rotating die as It spins, and the mandrel stops the walls collapsing at the point of bending. The pressure clamp travels with the tube

Tubular metalwork consists of mainly

to maintain an accurate and wrinkle free

bending,press braking (page 148) and arc welding (page 282). Press braking is capable of producing taperedhollow

bend. An additional clamp Is sometimes required to prevent wrinkling on the

The size of the rotating die determines the radius of the bend. The distance travelled determines the angle of bend.

m o

z D

Case Study

Mandrel bending the S4.3 chair Mart Stam designed the S43 chair (image 1),

to forming, because it is much more easily

and back are laminated, CNC machined and

which was introduced by Thonet in 1931. In

done at this stage. The blank is loaded by

lacquered in preparation (images 12 and 13).

1926 it began as a chair made from straight

hand over the mandrel and into the pressure

The final parts are brought together and

sections of gas pipe connected with cast

clamps (image 4).

assembled with rivets (image 14), The careful

'eibows'.The design was later refined and

The CNC machine aligns the tube and

design, refinement and production of this

produced by Thonet from a single, continuous

the bending sequence begins.The first bend

chair make the process look easy. The final

bent steel tube. It has since been made using

is made at the start point (image 5). From

product is simple, lightweight and uses the

the same technique; the only difference is

there, the blank is extended and twisted to

minimum material (image 15).

that new technology is making the process

the second bend point and so on (images 6,

faster and more accurate. The majority

7 and 8). The operation is precisely controlled

of mandrel bending is still performed on

and there is no scrap; the bending process

semi-automated machines because set ud

uses the entire length of tube. When the

time is quicker and tooling is less expensive.

process is complete the bent structure is

However, it is much more cost effective in the

removed by hand and each piece is checked

long run to produce large volumes on fully

for accuracy (image 9) and then hung up

automated machines.

(image 10).

The steel tube, or blank (image 2), is carefully cleaned and polished (image 3) prior

Featured Manufacturer

Thonet www.thonet.de

The bent metal forms are metal plated prior to assembly (image 11). The wooden seat

TECHNICAL DESCRIPTION

Ring Rolling Process

Metal section

Ring rolling is much simpler than mandrel bending in operation. The tube, profile, or sheet is passed between 3 rollers. One of the rollers,

in this case the bottom right, is moved Inwards to make the bend tighter.

The radius of the bend is decreased gradually over several cycles to avoid

cracking or wrinkling the metal. The blank is rolled back and forth until the curve meets the required shape.

Case Study

Ring rolling In this process metal tube is cut to length (image 1) and fed into the rollers. The rollers are adjusted to gradually bend the pipe into the desired radius (image 2), As the rollers move closer together the radius of the bend will be decreased. These are parts of a larger structure,

which do not require a tight radius (image 3), In this case the process is being

Dynamic rotating roller

used to bend tubular steel; a range of profiles and flat sections can be bent, but

Rotating cores (spindles)

require rollers with fitting profiles.

The aesthetic quality of manual

tooling can be very expensive, especially

or sheet,The thickest solid section that

operations, such as mandrel bends, is

for large section bending). It is possible

can be ring rolled is 80 mm (3.15 in.),

largely dependent on the skill of the

to form either a specific section or the

whereas roll forging can produce solid

operator and their experience with the

complete length; metal rings can be

parts of up to 150 tonnes (165 US tons).

particular machine set up.The dies are

formed along their entire length and

Roll forging is sometimes referred to as

often not exact, so an operator must

welded (see image, left).The radius does

'ring rolling', which can be confusing.

know how to compensate for optimum

not have to be constant; this process

bend angles. Automated and CNC

can be used to produce arcs that do not

operations are more precise.

fit into a circle.This technique is used

to the length apiece of material once it

COSTS

predominantly in the construction

has been bent.

Standard tooling is used to produce

are solid and ring rolled parts are hollow

QUALITY Applying a bend to a sheet of material increases its strength; these processes

DESIGN OPPORTUNITIES

combine the ductility and strength of

Mandrel bending is more versatile than

metals to produce parts with improved rigidity and lightness.

ring rolling for certain applications;

industry for structural beams.

In mandrel bending, the maximum

are bending lengths or forming rings.

size of tube is typically 80 mm (3,15 in.), but depends on the tooling available.

a variety of bend radii can be applied

Lengths of tube up to i m (3.3 ft) in

Wall thickness ranges from 0.5 mm to

to a single length of metal across any

diameter can be bent. Alternatively,

2 mm (0.002-0.079 in.).

axis. However, it is limited to relatively

metal sheet 4.5 m (14.8 ft) wide can be

The 2 main functions of ring rolling

Minimum bend radius is typically

a wide range of bent geometries.

Specialized tooling will increase the unit price considerably,but will depend on the size and complexity of the bend. Cycle time 1s rapid In most operations. Labour costs are high for manual

small diameter tube and can only form

rolled to form a tube, or cone, in materials

around 50 mm (2 in.). However,bends

operations, because a high level of skill

bends up to 200 mm (7.87 in.) radius. It

have to fit into the equipment; in other

and experience is required to produce

is suitable for one-offs, batch and mass

up to 80 mm thick (plate rolling), Lengths of metal, including profile, tube

words, several bends in close proximity

accurate bends,

production.

and sheet, can be rolled into rings, the

may not be feasible.

The advantage of ring rolling is that it is capable of producing a range of bends

maximum radius of which is determined by the capabilities of the manufacturer,

in almost any metal profile (although it must be remembered that specialized

Left Continuous circular metal profiles, such as these heating elements,

are produced by ring rolling and then arc welding the seam.

Mandrel bending is capable of

ENVIRONMENTAL IMPACTS

producing tight bends because the

Bending, as opposed to cutting and

internal mandrel prevents wrinkling

weld1ng,1s generally less wasteful and a

DESIGN CONSIDERATIONS

and failure. Ring rolling does not use a

more efficient use of energy. There is no

All of the bending processes stretch

mandrel and so is generally limited to

scrap produced in the bending operation,

material on the outside of the bend and

bend radii above 200 mm (7.87 in.).

although there maybe scrap produced in the preparation (of a blank for instance)

COMPATIBLE MATERIALS

and subsequent finishing operations.

compress material on the inside of the bend. However, metal is more willing to stretch than compress. Therefore, a bent

Almost all metals can be formed in this

piece of metal will be slightly longer,

way including steel, aluminium, copper

especially the outside dimension. This

and titanium. Ductile metals will bend

means that the length of a piece of

more easily.

material on a drawing rarely corresponds

Featured Manufacturer

Pipecraft www,pipecraft,co.uk

Rotary Swaging Process

Hammer block

Forming Technology

Swaging

Channel

There are 2 swaging techniques, hammering and pressing. These processes are used to reduce or expand metal pipe into tapers, joints or sealed ends.

INTRODUCTION

Pressing is a hydraulic operation and

Swaging is the manipulation of metal

is often referred to as'endforming'.The

tube, rod or wire, in a die. It is typically

pressing action is applied from multiple

used to reduce cross section by

angles simultaneously and can be used

drawing out the material, but pressing

to expand or reduce the diameter of pipe,

Die opening control key Open

techniques are also capable of expanding

the diameter of pipe by stretching. Hammering techniques are a rotary

TYPICAL APPLICATIONS Applications for swaging are diverse.

TECHNICAL DESCRIPTION

Cost

Typical Applications

Suitability

operation, known as rotary swaging and

It is used to form large parts such as

In rotary swaging, the metal is

and the hammer block rolls fall between

• Low to moderate tooling costs • Low to moderate unit costs

• Probes and spikes • Rigging • Telescopic poles

• One-off to high volume production

tube tapering.The ideal angle of taper

cylindrical lampposts, connectors

manipulated by a hammering action. This

the annular rolls, determines the size

is no more than 300,but it is possible to

andjoints for load bearing cables,

is generated by hammer blocks, which

of the tube that can be swaged. The

swage up to 450 where necessary. Smaller

and piping for gas and water. It is also

move in and out on the hammer block roll

dies are machined from tool steel (see

widely employed for small and precise

as the spindle head rotates rapidly.

image, belowl.

Quality • High precision

Related Processes • Arc welding • Tube and section bending

Speed • Rapid cycle time, but depends on complexity of operation

angles are simpler, quicker and more cost effective to produce. Rotary swaging is

products such as ammunition casing,

capable of producing sealed ends in pipe.

electrodes for welding torches and

The die opening, which is at its full extent when the spindle head rotates

thermometer probes. Swaging is used a great deal to form Right

joints.There are 2 main types of joint,

Fresh dies are machined

friction fit andformed. Friction fit joints

from tool steel for each

can be taken apart any number of

application, because

times, whereas formed joints tend to be

it is uncommon for 2

swaged products to

permanent. Friction fit examples include

be alike.

tent poles, walking frames, crutches and other telescopic parts. Formed joint examples include swaging a metal

lug or terminal onto cable for rigging

expensive and specialized. Applications

(sometimes known as atalurit splice),

include automotive chassis and high end

electrical cables and throttle cables.

bicycle frames.

Tubes can also be swaged together to form apermanent joint.

QUALITY Swaging compresses or expands metal

RELATED PROCESSES

during operation. Steel work hardens

Swaging is the most rapid and widely used method for tapering and end

in these conditions, which improves its

forming.Tapered metal profiles can

mechanical properties.

Components are typically produced to

DESIGN OPPORTUNITIES

also be produced by ring rolling plate

tolerances of o.i mm (o.oo4in.).They can

It is possible to rotary swage tapers along

(see tube and section bending, page

be made even more accurate, but this

the entire length of pipe. For example,

98) and arc welding (page 282) the

will increase cycle time considerably.

if the maximum length of swage on a

seam. Hydroforming is a recently

Ultimately, the quality is dependent

particular machine is 350 mm (13.78 in.),

developed process that is capable of

on the skill of the operator. The surface

forming complex hollow parts from

finish is generally very good and can be

stages. End forming, on the other hand,

tube. However, it is currently much more

improved with polishing (page 376).

is generally limited to short lengths of

then longer tapers are made in 2 or more

Case Study

Rotary swaging steel pipe Rotary swaging is capable of forming not only open-ended tapers but also sealed

ends in a length of pipe. This is especially useful for hollow probes and spikes. In the first images, 25 mm (0.98 in.) diameter tube (image 1) is being formed into a 30° taper to a sealed end.The pipe

is forced into the swaging die as it rotates at high speed (image 2). After 20 seconds or so, the pipe is retracted fully formed (image 3). The last 10 mm (0.4 in.) is likely to be solid metal. Small diameter tube is rotary swaged using the same technique (images 4 to 6). In this case the finished part does nothave a solid sealed end (image 6).The CO

diameter of the hole at the end can be

o

[n made precise by swaging the pipe over metal wire.

deformation due to the pressure that

rotary swaging and end forming can

COMPATIBLE MATERIALS

ENVIRONMENTAL IMPACTS

is required.

accommodate diameters over 150 mm,

Almost all metals can be formed in this

Th ere i s very 1 ittl e waste m ade by

(5.91 In.) such aslampposts.They can

way including steel, aluminium, copper,

swaging. It is not a reductive process like

MIG welding (page 282), are formed in a

also form very fine wire, as small as 1 mm

brass and titanium. Ductile metals will

machining. In fact, the hammering or

rotary swage die over an Internal die.This

(0.04 In.) diameter.

swage more easily. Tube, rod and wire are

pressing action can strengthen the metal

all suitable for swaging.

blank, contributing towards a longer

Precision parts, such as nozzles for

ensures maximum precision on both the inside and outside measurements.

Material thickness is also determined

by the capabilities of the swager.The gauge of material affects the ability of

lasting product.

COSTS

Rotary swaging is generally a

DESIGN CONSIDERATIONS

the pipe to be formed. There is no rule of

Metal is more willing to stretch than

thumb as to whether thicker of thinner

depends on the length and complexity

can cause 'white finger', especially In

to compress, so swaging tends to draw

gauges are more suitable because both

of the swage.

larger parts.

out metal into longer lengths.Therefore

thread tapping and hole making should

can be formed equally well.The benefit of thicker wall sections is that there is

be carried out as secondary operations.

more material to manipulate, but It will

operations because a high level of skill

take more hammering or pressing. Each

and experience 1s required to produce

design must be judged on Its merits.

accurate parts.

The machinery determines the

feasible diameter of metal blank. Both

Tooling is generally Inexpensive, but

manually operated process.The vibration

Cycle time is rapid. Labour costs are high for manual Featured Manufacturer

Elmill Swaging www.elmill.co.uk

r Hydraulic Swaging Process Reducing

Expanding

Open

Open

TECHNICAL DESCRIPTION In hydraulic swaging the pressure is applied

guide block is wedge shaped and forces the

to either the inside or the outside of the

die to either contract or expand. The die

pipe diameter. It is typically applied from at

determines the shape and angle of swage,

least 5 die segments simultaneously, which

which can be parallel or tapered.

surround the pipe wall. Turning the pipe

For parallel end forming, such as joint

during forming ensures even deformation

forming, standard tools are available for

of the wall section.

each pipe diameter. Tapered swaging

The hydraulic action is applied along the axis of the pipe being formed. The

Case Study

Hydraulic swaging Swaging dies are used to either expand the diameter of a pipe (images i, 2 and 3) or reduce it (images 4,5 and 6). The part is continuously rotated during operation to produce a uniform finish. Hydraulic swaging can be applied to a variety of profiles, including square and triangular sections, as well as round.

requires specially designed tooling.

Cold Roll Forming Process Roll formers driven

Upper roll former in highly polished hardened sleel

Upper roll former

Forming Technology

Roll Forming

Metal strip from coil

Leg

Finished profile

EJ

Sheet and strip metal can be formed into ribbed panels, channels, angles or polygons with progressive rollers. Such roll

Blind corners

forming is a continuous process capable of producing A,500 m (15,000 ft) of rolled steel per hour.

Workpiece I Lower roll former

Re-entrant angle (blind corner) formed by sequence of roll formers

Stage 1: Progressive roller A

Typical Applications

Suitability

• Automotive and transportation • Construction • Enclosures for white goods

• Batch production of minimum 1.500 m (5,000 ft)

Lower roll former

Stage 2: Progressive roller B

jj High specialized tooling costs Low to moderate unit costs

Quality • Good pitch accuracy (0.125-0.25 mm/ 0.005-0.01 in.)

Related Processes

• Very rapid, but depends on the complexity of bends and length of parts • Long changeover limes

process is suitable only for production

seam welded because they are formed to

runs greater than 1,500 m (5,000 ft).

As the name suggests, cold roll

maintain the enclosed shape.

The most significant consideration is

forming is carried out at room

Complex shapes with undercut

Speed

• Forging and extrusion • Metal stamping • Press braking

and box sections made in this way are

j:

TECHNICAL DESCRIPTION

that bends can onlybemadein the line

temperature. Sheet or strip metal

features (blind corners that cannot be

of production. They will have a radius

is generally fed into the roll forming

directly pressed by rollers), tight bends andhemmedjoints can be formed with

that is equivalent to, or greater than,

multiple roll formers in sequence.

process from a coil, and it Is bent

into the desired shape by a series of

_material thickness. The depth of cross-section will affect

progressive roll formers. However, it

INTRODUCTION

RELATED PROCESSES

combines the ductility and strength of

the costs of tooling. Parts are generally

is also possible to form precut sheets.

This metal sheet forming process is

Extrusion, press braking (page 148)

metal to produce parts with improved

process parts of any length can be made

designed so that their depth is less than

The bends are formed gradually over

used to produce 2D continuous profiles

and roll forging (see forging, page 114)

the opening to the roll former, in order to

several metres (yards); each set of

with a constant wall thickness. It will,

are all used to produce similar

rigidity and lightness. Cold working steel significantly

Because roll forming is a continuous

for example, bend metal strip (up to 0.5

continuous profiles to roll forming.

improves the grain alignment and thus

but they are generally limited to 20 m (66 ft) for ease of handling.The profile is cut to length as it is rolled and it is

m/1.6 ft wide) into continuous lengths

Short parts, cut to length during roll

the strength of the material.

possible to produce lengths as short as

of angle, channel, tube and polygon

forming, can also be made by metal

shapes. Roll formers (tools) are mounted

stamping (page 82). Roll forming is limited to profiles

The roll formers do not affect the

0.02 m (7.87 in.) at full speed.

surface finish of the metal being shaped,

ensure accurate and high quality bends in the workpiece.

The width of strip or sheet that can be processed is limited by the capabilities of the manufacturer. It is not uncommon

and angles are accurate to within +10

DESIGN CONSIDERATIONS

to be restricted to less than 0.5 m (1.6 ft)

with a constant wall thickness, whereas

andbetween 0.125 Tnm 0.25 mm

Tooling and changeover (set-up) is

wide. Multiple rolls alongside one

into ribbed, corrugated and crimped

extrusion and roll forging can be used

(0.005-0.01 in.).

expensive in roll forming and so this

another can form sheet materials over

patterns up to 1.4 m (4.6 ft) wide.

to produce profiles with varying wall

alongside one another so in a continuous process they can form sheet materials

DESIGN OPPORTUNITIES

that operates at speeds up to 1.25 m (4.1

produced by bending a single sheet of

Roll forming is used to make standard

ft) per second. Holes, ridges and other

material, such as an I-beam.

auxiliary patterning are carried out

Like roll forming, press braking can

The diagram illustrates 2 roll formers in a series of 8 or more. The roll formers are expensive because they are engineered to match

precisely. They are typically machined from hardened steel and polished to a very high finish. Water-cooling and lubricants reduce tool wear and help to

thickness and parts that cannot be

Rolling is a continuous operation

rollers is shaped to form the bend slightly more than the previous one.

Left

Highly polished roll

maintain high speed production. The roll formers, which are fixed

and custom-made products. Many items

forming tools such

in place, apply an even pressure on

are readily available, which eliminates

as these are used

the surface of the metal. Therefore,

to manufacture

produce continuous profiles. However,

tooling costs and minimum production

each bend is another operation in

volumes. However, new and original

TYPICAL APPLICATIONS

press braking, whereas roll forming is

Examples of cold rolled products include

continuous and therefore a much more

profiles can be designed and analysed using finite element analysis (FEA)

simultaneously to reduce cycle time.

roof and wall panels, lorry sidings, chassis

rapid production process.

software.Tooling is an investment that is offset by the volume of production.

for trains and cars, aerospace structural parts, shop fittings, structural beams

QUALITY

for construction and brackets and

Applying a bend to a sheet of material

range of profiles, from ribbed panels to

enclosures for white goods.

increases its strength; roll forming

channels and box sections. Hollow tube

This process can be used to produce a

continuous metal

profiles at speeds up to 4,500 m (15,000 ft) per hour.

symmetrical designs are simple to produce and less likely to have camber or curve.

Operations including punching and notching are integrated into the production cycle. Holes that are not

critical are precut into the flat metal to reduce roll forming cycle times.

o

o ?0

y Case Study

Roll forming an angle This simple roll forming process is used to

part (image 3). The finished parts are then

produce an angle within strip steel. A coil of

cut to length and stacked (image 4).

metal strip is loaded onto the tool (image i) and is then pulled through a series of 8

Varying levels of complexity, including hem, re-entrant and asymmetric profiles

progressive roll formers (image 2), in order

(image 5), can be achieved on thin-walled

to make this single bend. The formers are

parts formed by roll forming.

powered by electric motors, which drive each roll at exactly the same speed. Tension

is maintained by pressure on top of the coil. The finished part emerges from a die at the end of the production cycle, which ensures the dimensional consistency of the

this width but are more specialized and expensive to tool up for.

Sheet thickness for roll forming is typically limited to 0.5-5 (0.02-0.2

COSTS Specialized tooling will increase the unit price considerably, but will depend on the size and complexity of the bend. Tooling

in.). Bends should be at least 3 times

costs are generally equal to progressive

material thickness from the edge of the

tooling for metal stamping.

strip, otherwise it may not be possible to

Cycle time depends on the complexity of profil e, thi ckn es s of m etal an d 1 en gth

form the bend.

of cut-off. Simple profiles can be formed

COMPATIBLE MATERIALS

at up to 4,500 m (15,000 ft) perhour.

Almost all metals can be formed in this way. However, it Is most commonly

ENVIRONMENTAL IMPACTS

used for metals that are not feasible to

Bending is an efficient use of materials

extrude such as stainless steel, carbon

and energy. No scrap is produced in roll

steel and galvanized steel.

forming, although it may occur during

Featured Manufacturer

Blagg & Johnson www.blaggs.co.uk

machining or finishing operations.

Drop Forging Process Closed die forging Ram

Open die forging

Forming Technology

Forging

Upper die Hardened 1 steel

The forming of metal by heating and hammering or pressing was traditionally performed by blacksmiths on anvils. Nowadays, forgings are made by hammering, pressing or rolling hot metal

INTRODUCTION

.—. y-" '-7

metal

1

Metal has been forged into high-

billet 1

strength tools and implements for many centuries. Examples include horseshoes,

tool

,

\

/

Metal

Lower die is drawn out under

Flash

Anv"l

swords and axe heads, which were

with sophisticated dies and extreme pressure.

formed by blacksmiths hammering hot

Loading

Initial press

Loading

Completed forging

metal on anvils.There are now many

Typical Applications 1 Moderate to high tooling costs 1 Moderate unit costs

• Automotive and aerospace • Hand tools and metal implements • Heavy duty machinery

different types of forging, which are used

TYPICAL APPLICATIONS

Suitability

to produce an array of products from

The high-strength nature of forged metal

TECHNICAL DESCRIPTION

• All types of production

crankshafts to ice axes.The different

parts makes them ideal for demanding

The drop forging process is carried out

must be heated to over 1250°C (2282°F)

techniques can be dividedinto drop

applications and critical components

using either a closed or open die. An

and so stresses and wears the surface

forging, press forging and roll forging.

that require excellent resistance to

open die Is typically used for drawing

of the tool much more rapidly than

fatigue. Forged components are found

out (elongating a part and reducing its

aluminium, which is forged at only 500°C

an open or closed die operation.The

in lifting equipment, aerospace, military

cross-section), upsetting (shortening a

(932°F). During operation, lubricant that

processes forms hot metal billets

applications, cars and heavy machinery.

part and increasing its cross-section) and

acts as coolant is applied to the surface of

Many gears, plumbing parts, hand

conditioning (preparing a part for closed

the tool to cool it down and reduce wear.

Quality

Related Processes

Speed

• Excellent grain structure

• Casting • Machining • Tube bending (ring rolling]

• Rapid cycle time [typically less than a minute) depending on size, shape and metal

Drop forging is carried out as either

through repeated hammering.The main difference between the closed and open

die techniques is that open die forging is generally carried out with flat dies, where as closed die forging shapes metal

tools and implements are forged. Car

die forging). Open die forging is also used

axles and crankshafts are open die

to shape hexagonal and square section

forged. The heads of nails and bolts are cold forged.

by forcing it into a die cavity. Closed die

In drop forging, the ram brings the upper die into contact with the workpiece

bars. The tool face is generally square

under great pressure, from 50 kg/m2

or v-shaped for simple forming. The

to 10,000 kg/m2 (362-72,330 lb/ft2).

workpiece is repositioned between each

The force is generated by gravity fed

drop of the hammer by the operator. This

weights or by powered means (hydraulic

requires a great deal of operator skill

or compression) forcing the ram down.

and experience and is not suitable for

Press forging is powered by hydraulic

forging (also referred to as impression

RELATED PROCESSES

die forging) is used to produce complex

Forging is suitable for one-offs and low

and intricate bulk shapes. Open die

volume production as well as mass

forging, on the other hand, is typically

production runs. At low volumes it is an

used to 'draw out' a billet of metal into shafts and bars and can produce parts up

alternative to CNC machining (page 182), and at high volumes it competes with die

for high volume production. The tools are

hot or cold. Cold metal forging is typically

to 3 m (10ft) long.

or Investment casting (pages 124 and 130).

fabricated in tool steels (chromium-based

used for small parts, no larger than

Ring rolling as covered in tube bending

or tungsten-based) or low alloy steels.

10 kg (22 lb). The advantage of cold

(page 98) produces similar geometries to roll forging, but they require welding,

The life expectancy of a tool is largely

forging is that it can be used to produce

dependent on the shape of the part, but is

near net shape parts that do not require

whereas roll forged rings are seamless.

also affected by the ductility of the forging

secondary operations.

Press forging is essentially the same as drop forging, except that parts are formed by continuous hydraulic pressure, as opposed to hammering. Press forging

by the material, part size and geometry. Roll forging forms continuous metal

rams, which force the metal into the

in sections.

die cavity in a squeezing action. This

Closed die forging can be automated

technique can be used to process metals

material. For example, stainless steel

is used to shape hot and cold metals; the temperature of the metal is determined

automation. Long profiles can be forged

QUALITY By its very nature,forging improves grain

structure in the finished part. Metal

can be machined post-forging with no

tolerances increases costs. Forging is

parts through a series of metal rollers.

billets go through plastic deformation as

loss of quality because there are no voids

often combined with machining for

This process is used to forge straight

they are forged and as a result the metal

or porosity in the finished article.

Improved accuracy.

profiles andrings (washers), which can be up to 8.5 m (28 ft) In diameter and 3 m

produces exceptional strength to weight

(0.04 in.) in small parts up to 5 mm

DESIGN OPPORTUNITIES

and reduces stress concentrations that

(0.2 in.) in large parts,but vary according

Forging is suitable for low volume

tend to occur in corners and fillets. Parts

to requirements because reducing

production and one-offs.This is

grains align in the direction of flow. This

The tolerances range from 1 mm

Rollers draw out and reduce cross-section of metal

Roll Forging Process Billet cross-section

Profiled rollers shape metal bars

Finished profile cross-section

Drop forging a piston end cap

®or metal

'0 ® Stage 1: Reducing cross-section

In this case study a piston end cap is being

Stage 2: Profiling

is removed from the furnace with a pair of

closed dies. The metal billet is preformed and

tongs (image 2).

the scale is broken off 1n open die forging in preparation for closed die forging.

TECHNICAL DESCRIPTION Roll forging carried out as a continuous process. Metal bar or plate is fed into the

rollers, which draw out and profile the hot metal in stages. Each stage reduces the cross-section gradually, easing

the metal into the desired profile. This

forgings.They are joined together by upset forging a stopper on the shaft of the eyelet. Upset forging increases the cross-section and reduces the length of the shaft, a process similarto shaping the

such as aluminium and brass. Radii, however, are very important because

(19.7 ft) lengths (image 1), which are cut

of the part is changed but the volume

they encourage the flow of metal and

into billets. The size of billet is determined

stays the same. The metal spraying out

reduce tool wear.The minimum radius

by the weight and geometry of the part.

with impact is mill scale, which is formed

increases with depth of protrusion.

The billets are loaded into a furnace, which

as the steel surface oxidizes. This has to

heats them up to i25o'C (2282^). Each billet

be removed because otherwise it will

takes approximately 30 minutes to heat up

contaminate the final part.

COMPATIBLE MATERIALS

process is generally used to shape metal

Most ferrous metals, including carbon,

into simple continuous profiles.

no restriction on step changes in wall

alloy and stainless steels, can be forged.

thickness with this process.

Non-ferrous metals including titanium,

this way. First, a hole is punched in the

Forging can be used to make a

roll forged into the desired profile. This

geometries. Drop forgings can weigh

COSTS

is also known as ring rolling.

as little as 0.25 kg (0.55 lb) or as much as

Tooling costs are moderate to high,

5o kg (132 lb). Roll forging can produce

depending on the size and geometry of

seamless rings weighing more than

the part. Closed die forging tools typically last between 50 and 5000 cycles.Tool

life expectancies are affected by the

properties that cannot be manufactured

DESIGN CONSIDERATIONS

complexity of forging geometry, the

Designing for forging must take into

design of the forging cavities, sharpness

machined, but will have to compensate

account many factors that also affect

of radii, the material to be forged, the

for reduced strength resulting from

design for casting, including partition

temperature required to forge that

random grain alignment.

line, draft angles, ribs, radii and fillets.

material and the quality of the surface

Parts are formed by hammering, or

finish of the tool. Incorporating multiple

However, it is possible to form undercuts

pressing, which can produce surprisingly

cavities into a tool and pre-forming the

and joints with secondary forging

deep protrusions, up to 6 times the

metal billet increase the cycle time.

operations. An example of this is the

thickness of material. Draft angles can be

swivel link (see image,below).These are

minimized and even eliminated by clever

complete in less than a minute. However,

produced by first making 2 separate drop

design, especially in ductile materials

mass production forging can produce

Left To unite the 2 parts of the swivel link, the heated shaft of the eyelet is driven through the hole into a die that shapes the stopper.

1 vaA

aa

in any other way. Small volumes can be

Undercuts are not possible in forging.

.

o

huge range of component sizes and

because it produces parts with superior

11

copper and aluminium are also suitable.

middle of a forged disk, which is then

100 tonnes (110 US tons).

(image 3) and formed by repeated blows from the hammer (image 4). The shape

5 mm to 250 mm (0.2- 9.84 in.).There is

Seamless rings can also be formed in

The metal is aligned in the open die

The mild steel is delivered in 6 m

head of a bolt.

Typically, wall thickness should be

sufficiently for forging. The 'cherry red' billet

drop forged in a combination of open and

Cycle time is rapid. A typical forging is

parts in less than 15 seconds. Labour costs are moderate to high

duetothelevel of skill andexperience required.This is a relatively dangerous process, so health and safety depend on

the abilities of the workforce.

ENVIRONMENTAL IMPACTS A great deal of energy is required to heat metal billets to working temperature and hammer or press them into shape. No material is wasted because all scrap and off cuts can be recycled.

cd

I

The part is now ready for the dosed die forging process (image 5). The floor shakes with the impact of the hammer (image 6), With each cycle the hot metal is forced further into the upper and lower die cavities. Once the flash has

formed, it cools more rapidly than the rest of the metal because it is thinner and less ductile. Therefore, the remaining

hot metal is maintained within the die cavity and is forced into the extremities of it with each repeated blow from the hammer (images 7 and 8). It is a gradual, but rapid process. In

this case the metal does not need to be reheated at any point and so the entire forging operation is complete within 30 seconds. Due to the depth of this forging it must be carried out while the metal is 'cherry red'. The extremities are the first to cool off, and can be seen as

duller patches (image 9). These lumps of metal are too heavy for a single operator to manhandle with tongs, so they have to work In pairs to move the metal between workstations

(image 10). it requires a great deal of skill and experience to work in this environment. The flash is sheared off In a punch (image 11) and the part, which Is still very hot, is dispensed (image 12).

t '

Featured Manufacturer W. H. Tildesley www.whtildesley.com

designed parts with sufficient draft

TYPICAL APPLICATIONS

which causes porosity. When the parts

angles will result in higher quality parts.

Sand casting is used a great deal in the

are removed from the sand molds the

automotive industry to make engine

surface finish is distinctive, so all cast

to shape metals. Glass can also be cast in

block and cylinder heads, for example.

parts are blasted with an abrasive.

this way, but because of its high viscosity it will not flow through a mold.

Other applications include furniture,

lighting and architectural fittings.

Varying grits are used to produce the highest quality finish. Parts can then be polished to achieve very high surface

of the sand casting and investment

RELATED PROCESSES

finish. Because sand casting relies on

Sand casting is most commonly used

Forming Technology

Sand Casting

Evaporative pattern casting is a hybrid

Molten metal is here cast in expendable sand molds, which are broken apart to remove the solidified part. For one-off and low volume production this is relatively inexpensive and suitable for casting a range of ferrous metals and non-ferrous alloys.

Costs 1 Low tooling costs 1 Moderate unit costs

Quality • Poor surface finish and high level of porosity.

Typical Applications • Architectural fittings • Automotive • Furniture and lighting

Related Processes • Centrifugal casting • Die casting • Forging

Suitability • One-off to medium volume production

Speed • Moderate cycle time (30 minutes typically), but depends on secondary operations

casting (page 130) processes, and it can

Die casting (page 124), centrifugal casting

gravity to draw the molten material into

INTRODUCTION

beinexpensive. Instead of a permanent

(page 144) and forging (page 114) are all

the mold cavity, there will always be an

Sand casting is a manual process used

pattern, evaporative pattern casting

alternatives to sand casting metals. Sand

element of porosityin the cast part,

to shape molten ferrous metals and

uses an expendable foam pattern (often

casting is often combined with forging

non-ferrous alloys. It relies on gravity to

polystyrene), which is embedded in the

or CNC machining and arc welding (page

DESIGN OPPORTUNITIES

draw the molten material into the die

sand mold. The foam pattern istypically

282) to create more complex parts. Die

There is plenty of scope for designers

cavity and so produces rough parts that have to be finished by abrasive blasting,

formed by CNC machining (page 182) or injection molding (page 50).The molten

casting produces parts more accurately

using this process. For low volume

and rapidly and so is generally reserved

production it is generally less expensive

machining or polishing.

metal burns out the foam pattern as it

for high volume production.

than die casting and investment casting.

The sand casting process uses regular

is poured in. Parts made in this way have

Draft angles are required on the sand

sand, which is bonded together with

inferior surface finish, but this technique

QUALITY

mold to ensure removal of the pattern.

clay (green sand casting) or synthetic materials (dry sand casting) to make the

is very useful for prototyping, one-off and

The quality of surface finish and

The cores also require draft angles so that

manufacturing very low volumes.

mechanical properties depend largely

they can be removed from their molds.

molds. Synthetic sand molds are quicker

on the quality of the foundry. For

However, multiple cores can be used

to make and produce a higher quality

example, nitrogen is pumped through

and they do not have to correspond to

surface finish. However, the quality of the

molten aluminium to remove hydrogen,

external draft angles because the mold

casting is largely dependent on the skill of the operator in the foundry. There are many variables in the

TECHNICAL DESCRIPTION

casting process that the designer can

The sand casting process is made up of

do nothing about, although properly

2 main stages: moldmaking and casting.

Sand Casting Process Molten metal poured into runner

In stage 1, the mold is made in 2 halves, known as the cope and drag. A metal casting box is placed over the wooden pattern and sand is poured in and compacted down.

For dry sand casting the sand has a vinyl ester polymer coating, which is room temperature cured. The polymer coating on

each sand particle helps to achieve a better finish on the cast part because it creates a

film of polymer around the pattern, which forms the surface finish in the cast metal.

Stage 1: Moldmaking

Stage 2: Sand casting

For green sand casting, the sand Is mixed

with clay and water until it is sufficiently wet

In stage 2, the 2 halves of the mold are

the metal at the top of the mold molten for

to be rammed into the mold and over the

clamped together with the cores in place.

longer. This means that as the metal inside

pattern. The clay mix is left to dry so that

The metal is heated up to several hundred

the mold solidifies and shrinks as it cools

there is no water left in the mix. Water must

degrees above its melting temperature. This

it can draw on surplus molten metal in the

be removed because otherwise it will boil

is to ensure that during casting it remains

runner and risers. Porosity on the surface

and expand during casting, thereby causing

sufficiently molten to flow around the mold.

of the part is therefore minimized.

pockets of air in the mold.

A predetermined quantity of molten metal

Meanwhile, sand cores are made in

is poured into the runner, so it fills the

separate split molds and then placed In

mold and risers. Once the mold is full an

the drag. The runner and risers, which

exothermic metal oxide powder is poured

are covered with an insulating sleeve, will

into the runner and risers, which burns

already have been built into the pattern.

at a very high temperature and so keeps

is broken to remove the solidified metal

Case Study

parts.This means that complex internal shapes can be formed, which may not be

Sand casting a lamp housing

practical for the die casting processes. Sand casting can be used to produce

The casting temperature of aluminium is

in this case) is poured into the runner and

much larger castings than other casting

between 7300C and 78o0C (1346-1436^), yet

risers (image 10). The powder burns at a

methods (up to several tonnes).The

in preparation the aluminium is heated up

very high temperature, which keeps the

molds for castings can weigh a lot more

to more than 900°C (i652°F) in a kiln (image

aluminium molten in the top ofthe mold

than the casting itself. It is therefore not

i).The mold is prepared by placing a metal

for longer. This is important to minimize

practical or economical to produce very

casting box over the pattern (image 2). Sand

porosity in the top surface of the cast part.

large castings any other way.

coated in afiim of vinyl ester is poured

After 15 minutes the casting boxes are

over the pattern (image 3).The box is filled

separated along the partition line and

DESIGN CONSIDERATIONS

incrementally and rammed down after each

the part is revealed - covered in a layer of

Many design considerations must be

fill (image 4). The quality of the fill and so

charred sand (image 11).The sand is broken

taken into account for sand casting parts.

the quality ofthe final casting are largely

away from around the metal casting

dependent on the skill ofthe operator

(image 12). The surface finish is relatively

These include draft angles (range from 1° to 5°, although 2° is usually adequate), 1 ribs, recesses, mold flow and partition

(image 5). The vinyl ester cures at room

good and so little finishing is required. The

temperatures and solidifies rapidly.

parts are cut free from the runner system

In the meantime, the cores are prepared

lines. The part must be designed to take

COSTS

into account all aspects ofthe casting

Tooling costs arelowforone-offandlow

process,from patternmaking to finishing.

volume production, the main cost being

These elements affect the design and so

for patternmaking, which is inexpensive

rammed to compact it (image 6).The mold

all parties should be consulted early on in

compared to die casting tooling. Low

can be opened almost immediately. The core

the design process for optimum results.

cost patterns can be machined in wood

can then be removed (image 7), but it is still

or aluminium. Foam patterns for the 4

very delicate at this stage and so must be

2.5mm up to 130mm (1-5.12 in.). Changes

evaporative pattern method are the least

handled carefully.

in wall thickness are best avoided,

expensive of all.

The wall thickness that can be cast is

although small changes can be overcome

Cycle time is moderate but depends

in a separate mold. They are made with the

metal is poured into the runner (image 9),

minutes, but secondary and finishing

material ofchoice at the design stageto

the majority of this process is manually 5

ensure accurate castings in the selected

operated and the quality of casting is affected by the skill ofthe operator.

material. Steel will shrink nearly twice as

cn

brought together and clamped. Hot molten where it spreads through the mold and

Labour costs can be high, especially as

>

Once the cores have been placed into

Casting usually takes less than 30

Therefore it is essential to know the

CO

the drag (image 8), the mold is ready to be

in cross-section is required, then parts

operations increase cycle time.

>

carefully packed into the mold cavity and

on the size and complexity ofthe part.

Metals cool at different rates.

(/).

same sand coated in vinyl ester.The sand is

with tapers and fillets. If a large change are often cast separately and assembled.

(image 13) and are now ready for abrasive blasting and finishing (image 14).

up the risers. When the mold is full an exothermic metal oxide (aluminium oxide

much as aluminium and iron, whereas brass will shrink about 50% more than

ENVIRONMENTAL IMPACTS

aluminium. Shrinkage increases with

Alarge percentage of each casting

cross-section and part size.

solidifies in the runner and risers. This material can be directly recycled in most

COMPATIBLE MATERIALS

cases.The mold sand can be reused by

This process can be used to cast ferrous

mixing it with virgin material. In green

metals and non-ferrous alloys.The most

sand casting up to 95% ofthe mold

commonly sand cast materials include

material can be recycled after each use.

iron, steel, copper alloys (brass, bronze)

Energy requirements for sand casting

and aluminium alloys. Magnesium

are quite high because the metal has

is becoming increasingly popular,

to be raised to several hundred degrees

especially in aerospace applications

above its melting temperature.

because of its lightness.

Featured Manufacturer Luton Engineering Pattern Company www.chilterncastingcompany.co.uk

Die casting is a precise method of forming parts from metal. This high speed process uses pressure to force molten metal into reusable steel molds, to create intricate and complex 3-dimensional geometries.

Typical Applications

Suitability

• Automotive • Furniture • Kitchenware

• High volume production

Quality

Related Processes

Speed

• Very high surface finish • Variable mechanical properties

• Forging • Investment casting • Sand casting

• Rapid cycle time that depends on size and complexity of part

High tooling costs Low unit costs

INTRODUCTION

Gravity die casting is also known as

There are various techniques in die

permanent mold casting; steel molds

casting, including high pressure die

are the only feature that differentiate

RELATED PROCESSES Forging (page 114), sand casting and investment casting (page 130) are

casting, low pressure die casting and

it from sand casting (page 120).The

alternative processes. However, die

gravity die casting. High pressure die casting is a versatile

molds can be manually operated or

casting is the process of choice forlarge

automated for larger volume production.

volume production of metal parts due to

process and the most rapid way of

Reduced pressure means that tooling

its versatility, speed, quality, minimum

forming non-ferrous metal parts. Molten

and equipment costs are lower, so

wall section, high strength to weight and

metal is forced at high pressure into

gravity die casting is often used for short

repeatability.

the die cavity to form the part.The high

productions runs, which would not be

pressures mean that small parts, thin

economic for other die casting methods.

wall sections,intricate details andfine surface finishes can be achieved.The tooling and equipment is very expensive, and so this process is suitable only for high volume production. In low pressure die casting molten

Die casting is often compared to

injection molding (page 50).The main differences are related to the material

TYPICAL APPLICATIONS High pressure die casting is used to produce the majority of die cast metal parts such as for the automotive

qualities. Compared to plastics, metals are more resistant to extreme temperatures, they are durable and have superior electrical properties.

industry, white goods, consumer

Therefore, die castings are more suitable

material is forced into the die cavity

el ectroni cs, packagin g, furn iture,

for applications that demand these

by low pressure gas.There is very little

lighting, jewelry and toys.

properties such as engine parts.

turbulence as the material flows in

Low pressure methods are widely

and so the parts have good mechanical

utilized in the automotive industry

properties. This process is most suitable

to make wheels and engine parts,

QUALITY Die cast parts have superior surface finish, which improves with pressure.

High speed injection methods cause turbulence in the flow of metal, which can lead to porosity in the casting. Voids and porosity are an inevitable part of

Right Strength analysis of Chair One shows the resilience of the structure. This software

is used to double check that the engineering of the product is correct before manufacturing the tools for casting.

S, Miees SHEG, ( fraction = ( Ave. Crit. : 75%) - +1.65e+008

H +1. 50e+008

. 38e+008 .25e+008 +1.13e+008

a +8.00e+008 .75e+007 .50e+007 .25e+007 .006+007 .75e+007 .50e+007 .256+007 .006+000

metal casting that can be limited when engineering the product at the design stage. Mold flow simulation is used to

optimize the filling of the cavity of the mould and eradicate any potential voids and porosity. Strength analysis is carried out prior to manufacture to test the

for rotationally symmetrical parts in low

for example.They are also used to

melt temperature alloys. A good example

make products for the home such as

mechanical properties of the part (see

would be an aluminium alloy wheel.

kitchenware and tableware.

image, right).

a

k"

Low Pressure Die Casting Process

High Pressure Die Casting Process

Water cooling channels

Partition line Water cooling channel

Cold chamber method

Part ejected mold platten

Hydraulic rams provide clamping force

Moving mold platten

Die cavity Ejector pins

Runner system Part ejected

Die cavity Hydraulic rams provide clamping force

Molten metal

Runner system

Shot piston Remaining molten metal

Gas pressure i

Stage 1: Metal injection

Stage 2: Part ejected Stage 1: Metal injection

COMPATIBLE MATERIALS

TECHNICAL DESCRIPTION

Stage 2: Part ejected

TECHNICAL DESCRIPTION

High pressure die casting is carried out as

In the hot chamber method the shot cylinder

have to be trimmed before the part is ready

Choice of material is an essential part

In low pressure die casting the mold and

half of the mold is raised and the part

a hot or cold chamber process. The only

is fed through the furnace. The hot liquid

for joining and finishing operations. High

of the design process in die casting

furnace are connected by a feed tube. The

ejected. The nature of this process means

difference is that in the hot chamber method

metal is forced into the die cavity by the

pressure die cast parts require very little

because each material has particular

mold is mounted on top of the furnace

that it Is most suitable for parts that are

the molten metal is pumped directly from

shot piston at high pressure. The pressure

machining or finishing, because a very high

properties to be exploited. Die casting

with a horizontal split line. In stage 1, the

symmetrical around a vertical axis.

the furnace into the die cavity. The machine

is maintained until the part has solidified.

surface finish can be achieved in the mold.

is only suitable for non-ferrous metals.

molten material is forced up the feed tube

sizes range from 500 tonnes (551 US tons) to

Water cooling channels help to keep the

The melting point of ferrous metals is

and into the die cavity by gas pressure on

more than 3,000 tonnes (3,307 US tons). The

mold temperature lower than the casting

too high, so liquid forming is carried out

the surface of the metal in the furnace.

required clamp force is determined by the

material and so accelerate cooling within the

by investment or sand casting, and solid

Gas pressure is maintained until the part

size and complexity of the part being made.

die cavity.

state forming by forging.

Metal ingots and scrap are melted

in stage 2, when the parts are sufficiently

together in a furnace that runs 24 hours a

cool, which can take anything from a few

day. In stage 1 of the cold chamber method,

seconds to several minutes depending on

a crucible collects a measure of molten

size, the mold halves open and the part

metal and deposits it into the shot cylinder.

is ejected. The flash and runner systems

Non-ferrous metals including aluminium, magnesium, zinc, copper,

lead and tin are all suitable for die casting.A1 uminium andmagnesium

has solidified. In stage 2, when the gas pressure

is released, the molten metal still remaining In the feed tube runs back down into the crucible. The casting is left for a short time to solidify before the top

are becoming popularfor consumer

electronics due to their high strength to weight properties.They are dimensionally stable, even at high

DESIGN OPPORTUNITIES

form thinner wall sections than other

toolmaking to finishing, so all parties

temperatures, resistant to corrosion

There are many advantages to using

casting processes. Parts are produced to

should be consulted early on in the

and can be protected and coloured by

die casting if the quantities justify it.

high tolerances and often require little or

design process for optimum results.

anodizing (page 360).

Intricate or bulky fabrications can be

no machining andfinishing.

Labour costs are low for automated die casting methods.

ENVIRONMENTAL IMPACTS

Casting is most suitable for small parts because the steel tooling becomes

COSTS

All the waste metal generated in casting

cast into the product.

very large and expensive for parts above

Tooling costs are high because tools

can be directly recycled.There is no loss of

g kg (20 lb). Side action and cores can

have to be made in steel to be able

strength and so the waste metal can be

material are seen as waste, whereas

DESIGN CONSIDERATIONS

increase the cost of the tool considerably.

to withstandthe temperature of the

mixed with ingots of the same material,

holes in die castings are savings because

This process has technical considerations

However,there maybe an associated

molten alloys. For gravity die casting,

melted down and recast immediately.

they are produced directly in the mold

similar to injection molding.These are

benefit if the same feature reduces

sand cores can be used for complex

This process uses a great deal of

and so reduce material consumption.

rib design, draft angles (1,5° is usually

wall thickness, by increasing strength,

shapes and slight re-entrant angles.

energy to melt the alloys and maintain

These processes can be used to

sufficient), recesses, external features,

for example.

redesigned to become more economic with improved strength and reduced

External threads and inserts can be

weight. For example, holes in sheet

Especially if a multiple cavity mold

produce complex shapes with internal

mold flow and partition lines.The part

is used, cycle time is rapid-from a few

cores and ribs. High pressure methods

must be designed to take into account

seconds to several minutes, depending

will reproduce very fine details and can

all aspects of the casting process, from

on the size of the casting.

them at high temperatures for casting.

r

Case Study

High pressure die casting Chair One This chair was designed by Konstantin

After 2 minutes the molds separate to

[T* I i 1

Grcic for Magis in 2001 and took 3 years

reveal the solidified part, which is collected

mlkztl

to develop from brief to production. It

by a robotic arm (image 4). Once the part

was designed specifically for die casting

has been extracted the mold is steam

in aluminium, which is a very common

cleaned and lubricated for the next cycle

material in high pressure die casting and

(image 5). Meanwhile, the part is dipped in

so is used in large quantities by foundries

water to cool it down and ensure that it is

(image i).The raw material (which may

completely solidified (image 6).

come from recycled stock) is melted in the

The flash and runner systems are

holding furnace and mixed with scrap

removed (image 7) and the scrap material

from the casting process. A crucible for

is fed straight back into the holding furnace

transferring the molten aluminium into

so that it can be recast. Although the

the shot cylinder lowers into the holding

stacked chair seats already have a very high

furnace and collects a measured charge of

surface finish (image 8), this is improved by

the metal (image 2). It is poured into the

polishing (page 376). Inserts are used in the

shot cylinder (image 3) and forced into the

tools so that different leg assemblies can be

die cavity by a shot piston. This machine has

fitted (image 9).

a clamping force of 1,300 tonnes (1,433 US tons), which is necessary for casting the 4 kg (8.82 lb) chair seat.

Featured Company

Magis www.magisde5ign.com

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Liquid metals are formed into complex and intricate shapes in this process, which uses non-permanent ceramic molds. It is also known as lost wax casting.

Typical Applications

Suitability

» Low to moderate cost wax injection tooling » Non-permanent molds 1 Moderate to high unit costs

• Aerospace » Construction • Consumer electronics and appliances

• Low to high volume production

Quality

Related Processes

Speed

• Die casting • Metal injection molding • Sand casting

» Long cycle time (24 hours)

1 Very high 1 Complex shapes with high Integrity

INTRODUCTION

TYPICAL APPLICATIONS

This is a versatile metal casting process. It

Applications are widespread and include

within 125 microns (0.0049 i11-) for every

There are many stages to the investment

by hand. The wax is injected at low pressure,

In stages 5 and 6, the wax patterns

is more expensive than die casting (page

products for the aerospace, automotive,

25 mm (0.98 in.) of cast metal.

casting process, which are divided into

and so there is little flash, or other problems

and runner system are melted out in a

124), but the opportunities outweigh the

construction, furniture, sculpture and

pattern making, ceramic mold making

that are associated with high-pressure

steam autoclave and the ceramic shell is

DESIGN OPPORTUNITIES

and casting.

injection techniques.

subsequently fired at 1095°C (2003°F1. It

price difference for many applications. Due to its many advantages,

jewelry industries. Parts include gears,

Dimensions are typically accurate to

housings, electronic chassis, covers and

Investment casting does not have the

investment casting is used to produce a

fascias, engine parts, turbine blades

same shape limitations as other casting

wide range of products from only afew

and wheels (see image, above), medical

techniques.This is because neither the

grams to more than 35 kg (77.16 lb) and

impl ants, brackets, 1 evers an d h an dl es.

less than 5 mm (0.2 in.) long up to over 0.5 m3 (17.66 ft3). Investment casting is made up of

pattern nor metal part has to be ejected at any point.The pattern and mold are

RELATED PROCESSES

both non-permanent: the wax is melted

Some parts made by investment casting

from the ceramic shell, which in turn

TECHNICAL DESCRIPTION

The wax parts are molded with the gate

is removed from the kiln at between SOCTC

formed, which in this case is wax injection.

and runner system attached. In stage 2, the

and 1095°C (932-2003°F)depending on the

The tooling is typically aluminium. Unlike

whole assembly is mounted onto a central

metal being cast.

conventional injection molding, these tools

feed system. Everything is wax and so can be

can have many parts, which are assembled

melted and joined together. Each assembly

In stage 1, the expendable pattern is

Itree) may hold tens or even hundreds

In stage 7, whilst the shell mold is still very hot, molten metal is poured in. In most cases gravity is used to fill the mold.

of products, depending on the size of the

It is also possible to pull the molten metal

parts, which increases production rates.

through using a vacuum, or force it into the

3 elements: expendable pattern, non-

are also suitable for die casting, sand

is broken from the cast part. In other

are used.These are Injection molded

permanent ceramic mold and metal

casting (page 120) or metal injection

words, it is possible to cast shapes with

separately and then over-molded with

dipped in ceramic slurry and then coated

casting.The patterns are typically

molding (page 136). When volumes

undercuts and varying wall thickness

conventional wax. When the casting is

with fine grains of refractory material.

cooled, in stage 8 it is broken out of the

injection molded (page 50) wax, but

exceed 5,000, production may shift to

that are not feasible with other liquid

complete it is submerged in water and

The primary coating is made up of very

shell mold using impact and vibration. For

other materials are also used, including

die casting if the design is suitable.

forming processes.This eliminates costly

the soluble wax melts away.

fine particles, which ensures a good

delicate parts, the shell is removed using

Injection molded wax is still the most

surface finish on the inside of the shell

chemical dissolution or high-pressure water.

commonly used pattern material. Other

mold. The number of coats depends on the size of part and the metal being cast.

rapid prototyped (page 232) models. Both small and large volumes can be

fabrication operations.

QUALITY

Complex internal shapes are feasible

accommodated, from prototypes to mass

Investment casting produces high

in the injection molding of the wax

materials and techniques include rapid

production of 40,000 or more parts per

integrity metal parts with superior

pattern.The molds are sometimes very

month. It is also possible to produce very

metallurgical properties.The surface

complex, consisting of many parts, to

prototyped wax (thermojet) and plastic models (quickcast), acrylic and machined

complex, intricate parts with thin and thick wall sections that cannot be cast in any other way.

finish is generally very good and is determined by the quality of the expendable pattern.

reduce assembly operations later on. For precise and critical internal geometries, soluble wax or ceramic pre-formed cores

or molded expanded polystyrene (EPS), known as lost foam casting. In fact, any material that can be burnt out and has a

In stages 3 and 4, the assembly is

mold under pressure.

Once the casting has solidified and

The individual parts have to be removed from the runner system and cleaned up.

This wet dipping and dry stuccoing

Machining is needed to clean up the surfaces

process, known as investing, is repeated

that were in contact with the runner system.

7 to 15 times with progressively coarser

The parts are then finished with abrasive

refractory materials. Between each

blasting (page 3881, or left 'as cast', because

cycle the shell is left to dry for 3 hours.

the surface finish is generally very good.

The simulation shows

potential problem areas in the original part.

Investment casting a window support

Left

CAD

The part is modified in

The assembly, known as a 'tree', is dipped

All parts are designed and developed on

by hand into a water-based zircon ceramic

ceramic. This is carried out automatically

shows that no problem

CAD. Flow simulation software is used to

solution (image 3). The primary coating

by a robot (images 6 and 7). The secondary

reduce problem areas such as porosity. The

is always carried out by hand because it

coatings are applied every 3 hours.

image sequence demonstrates this process.

is the most critical and essential for good

areas remain.

The original part (see image, far left) was

surface finish. The wax tree is transferred

gradually modified (see image, left). Areas of

into a coating chamber, which applies fine

potential porosity are highlighted in yellow.

refractory powder (image 4) and hung up to dry (image 5).

INVESTMENT CASTING This is the production of a 'spider' used in

the construction industry for supporting panes of glass. They are manufactured

in stainless steel and often finished by electropolishing (page 384). The expendable pattern is injection molded wax (image i) in a tool very similar to that used in conventional

injection molding. The process is fully automated, but molds with complex internal cores are manually operated.

The mold tool is 3% larger than the final metal casting, to allow for the wax sufficiently low coefficient of expansion

Cast parts are dimensionally accurate

for complex molds with removable

is suitable for the pattern, although some

and minimize machining operations.

core segments. A simple split mold is

materials will take longer than others to

However, internal threads and long blind

relatively low cost and has along life

burn out. Wax has proved to be the most

holes can only be formed on parts as a

expectancy, as the wax has alow melting

effective material for large volumes and

secondary operations.

temperature and in not very abrasive.

high surface finish.

As with other liquid forming processes, cast parts are typically ribbed

DESIGN CONSIDERATIONS

and reinforced to eliminate warping and

Wall sections do not have to have a

distortion when cooling.

Cycle time is long and generally 24 hours or more.

Investment casting is a complex process that requires skilled operators. Therefore,labour costs can be quite high.

uniform thickness; sometimes thicker sections are actually required to aid

COMPATIBLE MATERIALS

the flow of metal into the mold cavity.

Almost all ferrous and non-ferrous

ENVIRONMENTAL IMPACTS Very little metal is wasted in operation

It is possible to feed metal to the cavity

metal alloys can be investment cast.This

through multiple gates, ensuring good

process is suitable for casting metals that

and any scrap and offcuts can be directly

distribution around even complex parts.

cannot be machined and fabricated in

recycled 1n the furnaces.The melted wax

any other way such as superalloys.

is reused in the runner systems.

The wall thickness depends on the

alloy. The typical wall thickness for

coatings of a more substantial mullite

CAD. A new simulation

The most commonly cast materials

The ceramic shells cannot be recycled,

aluminium and zinc is between 2 mm

are carbon and low alloy steels, stainless

but their material is totally inert and

and 3 mm (0.079-0.118 in.), although it

steels, aluminium, titanium, zinc, copper

non-toxic.The smoke and particles

is possible to cast wall sections as thin

alloys and precious metals. Nickel, cobalt

produced by casting are captured by

as 1.5 mm (0.059 'n-)- Steel and copper

and magnetic alloys are also cast.

ceramic filtration.

alloys require thicker wall sections, typically greater than 3 mm (0.118 in.),

COSTS

but for small areas a thickness of 2 mm

There are tooling costs for the wax

(0.079 in.) is possible.

injection process.These can be moderate

to shrink 1% and the metal to shrink 2%. The wax patterns, which are molded

with a gate attached, are assembled onto a runner system (image 2). The joint interface is melted with a hot knife and held together to form a bond.

At this stage the ceramic shell is very fine and has to be reinforced with secondary

After at least 7 coats the ceramic shells

heat as the molten metal is poured in. This

are sufficiently robust. Metals with higher

encourages the metal to flow through even

melting point and large parts require

the most complex shapes.

more coats. The wax is removed In a steam

The mold is left to cool for approximately

autoclave and recycled. The hollow ceramic

3 hours (image ii).The ceramic shell is broken

shell is placed in a kiln at 109 50C (20 030F) to

from the solidified metal with a pneumatic

harden it fully and remove any residual wax.

hammer (image 12).

It is an exact replica of the wax pattern.

The ceramic mold is red hot when it is removed from the kiln 3 hours later (image 8). In the meantime, the molten stainless steel is

prepared in a crucible, which is used to pour the metal into the mold (image 9).The metal is poured by hand into the mold (image 10). The ceramic molds retain a great deal of

The individual parts are removed from the runner system, ground off and polished up to produce the finished article (image 13).

to accommodate the plasticized powder

Metal Injection Molding Process

composite material. Powder parts

Moving core

In stage 1, the injection cycle is much the same as for other injection molding

Water cooling channels

Heater bands

processes, although the molded parts are

roughly 20% larger in every dimension

Hydraulic clamping arm

prior to heating and sintering. This is to allow for the shrinkage, which will take place as the binder is removed.

o

This process combines powder metallurgy with injection molding

In stage 2, the 'green' parts are heated

1

technology. It is suitable for the production of small parts in

In a special debind oven, to vaporize and remove the thermoplastic and wax binder. The molded parts are now in pure metal,

steel, stainless steel, magnetic alloys, bronze, nickel alloys

Die cavity filled under pressure

with all binder material removed. Mold tool

Support plate

and cobalt alloys. Stage 1: Injection molding

Stage 2: Heating and sintering

The final stage Is to sinter the parts in a vacuum furnace. This typically starts

with a nitrogen/hydrogen mixture, (depending on material type) changing to

High tooling costs Moderate to low unit costs

Typical Applications

Suitability

• Aerospace • Automotive • Consumer electronics

• High volume production • Low to medium volume production for certain applications

Quality

Related Processes

• Very high quality surface finish • High level of density

• Die casting • Forging • Investment casting

Speed

TECHNICAL DESCRIPTION

a vacuum as the sintering temperature

after sintering.This is normally readily

Fine metal powder, typically no larger

Increases. The 'green' part will shrink

removed after molding, but may be

than 25 microns (0.00098 in.) in diameter,

roughly 15-20% during sintering, to

problematic in surface textures and

is compounded with a thermoplastic

accommodate the loss of material during

threads. Incorporating flat areas in

and wax binder. The spherical metal

debinding. The resulting metal part has

particles make up roughly 80% of the

very little porosity.

threads and locating the partition line in

• Rapid cycle time similar to injection molding (30-60 seconds typically) • Debinding and sintering (2-3 days)

non-critical areas reduce such problems. After sintering, MIM parts are almost 100% dense and have isotropic

mixture. The manufacturers themselves

Certain parts, especially those with

often make up this feedstock and so the

overhanging features, are supported

exact ingredients are likely to be a well-

in specially designed ceramic support

guarded secret.

plates so that they do not sag at high

INTRODUCTION

TYPICAL APPLICATIONS

produce the intricate features and

characteristics. In other words, there

Metal injection molding (MIM) is a

MIM is capable of producing a wide

accuracy of MIM.

is very little porosity.This ensures the

powder process and a similar technique,

range of geometries and so is utilized

MIM reduces, or eliminates, the

structural integrity and ductility of the

known as powder injection molding

in many industries. The accuracy and

needfor secondary operations such as

metal part (see artwork, above, stage 2).

(PIM), is used to shape ceramic materials

speed of the process mate it ideal for

machining. It is capable of producing

and metal composites.

manufacturing components for the

parts with a complexity and intricacy that may not be feasible in any other

DESIGN OPPORTUNITIES

Left These bent samples

Design opportunities and consideration

demonstrate the

processes. Secondary operations can also

for MIM are more closely related to

structural integrity and ductility of

work out much more expensive for large

injection molding than to conventional

MIM material.

volumes of production.

metalwork. For example, MIM can

MIM combines the processing

advantages of injection molding with

aerospace, automotive and consumer electronics industries.

the physical characteristics of metals. It is thereby possible to form complex shapes,

RELATED PROCESSES

with intricate surface details and precise

Investment casting (page 130), die

dimensions. Parts are ductile, resilient

QUALITY

subsequent secondary operations of

and strong, and can be processed in the

casting (page 124),forging (page 114) and CNC machining (page 182) can be

Like injection molding, the high

conventional metalworking because

same way as other metal parts, including

used to produce similar geometries. In

pressures used in this process ensure

it can produce complex and intricate

welding, machining, bending, polishing

fact, investment casting and MIM are

good surface finish, fine reproduction of

geometries in a single operation.Tools

an d el ectropl ati n g.

often interchangeable, depending on

detail and, most importantly, excellent

can have moving cores and unscrewing

tolerances and intricacy of features.

repeatability. However, MIM has the

threads for example, making the

small components generally up to 100 g

While die casting can produce similar

same potential defects, including sink

inclusion of internal threads, undercuts andblindholes possible.

This process is suitable for forming

For MIM, the injection molding machines are modified slightly in order

temperature. Parts with flat bases usually do not require additional support.

reduce the number of components and

(3-53 oz). As with conventional injection

features and tolerances to MIM, it can be

marks, weld lines andflash. Unlike many

molding (page 50), MIM is predominantly

used only for non-ferrous materials, not

plastics, metal parts can be ground and

used for high volume production,

for steels and high melting point metals.

polished to improve surface finish.

although low to medium volumes can be

Forging is generally chosen for larger

viable where MIM offers technical, design

components, typically those weighing

Careful design will eliminate the

Complex tooling, because it comprises m ovin g parts, m ay in crease tool

costs significantly, but if it eliminates

needfor secondary operations.This is

secondary operations on the MIM parts

or production advantages over other

more than 100 g (3.53 oz), in ferrous and

especially important for flash at joint

the extra costs can be offset, particularly

manufacturing processes.

non-ferrous metals, but forging cannot

lines, which becomes a metal burr

where large volumes are required.

Left This range of parts has been produced by the MiM process.

Case Study a-EsoH

Metal injection molding a cog from a window lock mechanism The compounded metal powder and

ejector systems for intricate shapes (image 3).

causes the metal particles to fuse together.

thermoplastic and wax binder are formed

On release from the injection molding

The finished parts have a bright lustre

into pellets for Injection molding (image

equipment, the parts are a dull greyish colour

(image 6). They are solid metal, with very little

i).The metal powder is very fine and the

- which Is referred to as 'green' state - and

porosity. MIM parts have good mechanical

particles spherical to give a final dense

they are surprisingly heavy, due to their high

properties and are stronger and less brittle

sintered structure.

level of metal content. They are replaced onto

than conventionally sintered components.

The injection molding equipment Is

support trays, which are stacked up In the

similar to that used for plastic injection

debind oven (Images 4 and 5). This stage is

(image 2).The mixed materials are not

often manually operated, but Is suitable for

as fluid as thermoplastics. The tooling is

automation If the volumes justify it.

generally machined from tool steel and can have moving cores, inserts and complex

The binder is completely removed in the rn

debind oven, then high temperature sintering

o —j o o

r*

E3

Without any additional costs

A significant consideration and

problems. Like injection molding, the

COMPATIBLE MATERIALS

wall thickness should remain constant.

The most common metallic materials for

pi asti c in j ecti on, th e part 1 s m ol ded in

sintered it cannot be recycled so easily,

MIM are ferrous metals including low

30-60 seconds. Unlike injection molding,

but rejects are rare at that stage as parts

the parts need to have the binder

are accurate andrepeatable.

The plastic binder is vaporized during the debinding operation and collected in

textures and other surface details can be

limitation on the process is the size of

incorporated into the molding process,

part.The general size rangeisfrom o.i g

eliminating these as finishing operations.

to 100 g (0.0035-3.53 oz).or UP to 15° t11"11

and keep material consumption to a

alloy steels, tool steels, stainless steels,

To maintain a uniform wall thickness

Injection cycle time is rapid: like

recycled. Once the material has been

(5.91 in.) in length. Such size restrictions

minimum, it is necessary to core out bulk

magnetic alloys and bronze. Aluminium

removed and then be sintered, which is

relate to the sintering operation, which

parts with recesses, blind holes and even

and zinc are not suitable, and parts in

usually done over a further 2-3 days, as

produce these with a depth to diameter

removes the plastic matrix and causes

through holes.

these materials can usually be made as

the debinding time is 15-20 hours, plus

waste traps, without any environmental

ratio of up toiotoi.

the part to shrink considerably. Large

die castings.

several hours for sintering. Labour costs

problem.

Holes and recesses can be molded

into the metal part and it is feasible to

Internal corners are a source of stress

parts and thick wall sections are more

concentration and so should have a

DESIGN CONSIDERATIONS

likely to distort during the heating and

minimum radius of 0.4mm (0.016 in.).

COSTS

is often fully automated. However, MIM

Like conventional injection molding,

sintering process.

Outside corners can be sharp or curved,

Tooling costs are similarto plastic

requires sintering, which does Increase manual operations and so costs.

when designing for MIM it is essential

are low for injection molding because it

depending on the requirements of the

injection moldtools.The MIM materials

to involve the manufacturer in the

1 mm and 5 mm (0.04-0.2 in.). It is

design. Draft angles are not normally

are typically high cost, due to the level of

development process to ensure that

possible to produce wall thicknesses

required, except for long draw faces,

processing andpretreatment necessary

ENVIRONMENTAL IMPACTS

the part is designed to optimize the full

of 0.3 mm to 10 mm (0.012-0.4 in.), but

which makes the designer's job easier.

to make them suitable for the Injection

Scrap material in the injection molding

Wall thickness is generally between

Featured Manufacturer

Metal Injection Mouldings www.metalinjection.co.uk

advantage of the MIM process.

such extreme measurements may cause

molding operation.

cycle, including feeders, can be directly

Electroforming Process

Forming Technology

Electroforming Electroforming is electroplating onto non-conductive surfaces. The object being electroformed can be used as a mold, or encapsulated. Electroforming is an extremely precise technique for reproducing sheet geometries.

Costs

Typical Applications

Suitability

• Low tooling costs generally • High unit costs, partly dependent on electroforming material

• Architecture and interiors • Biomedical • Jewelry, silversmithing and sculpture

• One-off to batch production

INTRODUCTION

The electroforming process is carried

Electroforming is the same as

out in solution and on a mandrel.

electroplating (page 364), but it is carried

Therefore, part geometry is not restricted

out on non-conductive or non-adherent

by conventional mechanical problems

metal surfaces (such as stainless steel).

such as the application of pressure.

It is made possible by covering the non-

This means that a perfectly flat surface

conductive material (mandrel) with

is made in exactly the same way as an

a layer of silver particles. This forms a

undulating and intricate engraving.

surface onto which metal is deposited.

Adding ribs, recesses and embossed

TECHNICAL DESCRIPTION

design features affects neither the cycle

The difference in operation between

onto a plastic support, which holds them

time northe cost of electroforming.

electroforming and electroplating is that

in shape during electroforming. Rigid

the forming process is generally carried

plastics can be molded or machined and

out more slowly, for improved accuracy.

used for mandrels for more precise parts.

The process builds up the metal layer in a gradual andprecise manner.The electroformed product will be an exact

Quality

Related Processes

Speed

• Very high: exact replica of the mold with relatively uniform wall thickness

• CNC machining • Investment casting • Laser cutting and engraving

• Very long cycle time (a few hours up to several weeks), depends on the materials and thickness of electroforming

replica of the mandrel. It is suitable for

TYPICAL APPLICATIONS

very small parts as well as large and

Due to its exceptional accuracy,

complex shapes.

electroforming is used in applications

mandrel is connected to a DC power

builds up on the surface of the workpiece,

that are dimensionally precise. For

supply. This causes suspended metal ions

the ionic content of the electrolytic

in the electrolytic solution to bond with it

solution is constantly replenished by

and build up a layer of pure metal.

dissolution of the metal anodes, which

example, it is popular for biomedical equipment, microsieves, filters, optical equipment and razor foils. It is used to make tools for composite

laminating (page 206), embossing and metal stamping (page 82). Electroformed nickel tooling largerthan 1 m3 (35 ft3)

The coating on the surface of the

The mandrel is generally designed to be removed and reused; it may also

be permanently encapsulated within

As the thickness of electroplating

are suspended in the electrolyte in a perforated conductive basket.

The process is indefinite, although

the electroforming, or dissolved away.

wall thickness is generally between

Encapsulation can take place on almost

5 microns (0.00019 in.) and 25 mm (1 in.).

any material, including wood, plastic

Process time, which can take anything

can work out less expensive than CNC

and ceramics. An example of a mandrel

from a few hours to 3 weeks, is computer-

machining (page 182) steel mold tools

material is silicone rubber, which is

controlled to ensure a high degree of

frojn solid.

durable and reusable. They are mounted

accuracy and repeatability.

Decorative applications include interior fittings, sculptures, lighting, jewelry and tableware. Metal film props,

QUALITY

such as masks and goblets, are also made

holograms. Similar sheet geometries

in this way because electroforming

can be made by investment casting

The metals used in electroforming

can reproduce very fine details and is

(page 130), with its lost wax process, and

-nickel, copper, silver and gold - are

suitable for small batch production runs.

electroforming is sometimes used to

generally quite soft, with the exception

Examples of mandrels include molded

produce the molds for the wax patterns

of nickel, and so have to be built up in

rubber and wooden carvings. Either can

that are used for investment casting.

sufficient thicknesses to produce self-

be used to produce electroformings or

Electroforming mandrels are made

supporting structures.The metal content can be controlled with extreme precision:

by rapid prototyping (page 232), laser cutting and engraving (page 248),

for example, silver electroformed parts

RELATED PROCESSES ^

manual engraving, CNC machining,

are 100% silver, which is more than

Electroforming is unmatched in its ability

vacuum casting (page 40) and injection

sterling silver parts.

to reproduce the surface of a mandrel to

molding (page 50).

metal encapsulations.

within sub microns. It is used to replicate

The surface finish is an exact replica of the surface of the mandrel in reverse.

Case Study

Metal encapsulated wood with gold

Electroforming copper This silicone mandrel is a molding taken from

electroforming tank (images 4 and 5), where

This follows the same basic electroforming

which coat the object In water-based silver

a hand engraving (image i). It is the negative

the electrolytic solution is supplied with fresh

process as In the case study opposite except

nitrate and a reducing agent. Combined,

of the product, so will make replicas of the

ions by pure copper anodes (image 6). The

that the mandrel Is covered entirely by

they react to leave a thin film of pure silver

original as electroformings.

copper is deposited on the surface of the

a uniform metal layer and so cannot be

(image 3).This Is the same process as the

mandrel to form a uniform wall thickness.

reused. The permanently encapsulated

mirroring of glass.

The mandrel is coated with pure silver powder (image 2), which provides a base

mandrel is often used as a pattern to

After 48 hours this part will be

The metal encapsulated mandrel

onto which the copper will deposit and grow.

fully formed (image 7) and have a wall

make reusable mandrels for subsequent

is then ready to be coated in gold by

The whole face needs to be charged with

thickness of 1 mm (0,04 in.). It is then

electroforming operations.

electroforming. After processing, the part is

a DC electrical current, so copper wires are

removed from the mandrel, which can be

The original wooden carving (image 1) is

connected away from the critical face of the

cleaned up and reused. The electroformed

sprayed so It has a silver conductive surface

part, on the flange of the mandrel (image 3).

part is cleaned, too, and trimmed prior to

(image 2). The spray gun has 2 nozzles.

The mandrel Is then submerged in the

subsequent processing (image 8).

selectively polished to highlight the carving details (image 4).

DESIGN CONSIDERATIONS This process has high operating costs,

which do not come down significantly with an increase in volume. The wall thickness of an electroformed part is uniform. Depending on the requirements of the application,

4

these are typically between 5 microns (0.00019 in-) arici 25171171

(i in.) thick. The maximum size for electroforming

is determined by the tank size. Typically

Featured Manufacturer

this is up to 2 m2 (21.5 ft2). However, there BJS Company

are tanks large enough to form metal

www.bjsco.com

parts up to 16 m2 (172 ft2). At this size dimensional tolerance is reduced to 500 microns (0.019 i1"1-)- Parts electroformed in very large tanks can take up to 3 weeks

such as wood or metal, while others are

depending on the finishing involved.

made specially for electroforming, which

Some parts require a high level of surface

can be more expensive.

finish, which tends to be a manual job.

COMPATIBLE MATERIALS

BJS Company

Therefore, quality of finish is determined by the original product.

Labour costs are moderate to high

needs of the application. Featured Manufacturer

www.bjsco.com

produced directly from a carved master,

to form a sufficient wall thickness for the

Cycle time depends on the thickness

Almost any material, such as

of electroforming. It is also determined

ENVIRONMENTAL IMPACTS

wood, ceramics and plastic, can be

by the rate of deposition, temperature

Electroforming is an additive rather than

electroformed or encapsulated with

an d el ectropl ated m etal.

Wall thickness on a part is built up at

reductive process. In other words, only the required amount of material is used

base material with the decorative and

m etal. Any m ateri al th at can n ot be

manufactured in a relatively inexpensive

hardwearing properties of another

used as a mandrel can be reproduced

approximately 25 microns (0.00098 in.)

material, such as copper or nickel, which

material on the surface.

in silicone, which is also suitable for the

per hour for silver and up to 250 microns

electroforming process.

(0.0098 in.) per hour for nickel.The rate

of deposition will influence the quality

are carefully controlled with extraction

of the electroforming: slower processes

and filtration to ensure minimal environmental impact.

Electroformed products can be

DESIGN OPPORTUNITIES

can be deposited at faster rates than

Because mandrels can be made from

other metals. Once the process has been

Electroforming can be used to reproduce work that would take too long

semi-flexible rubber, intricate shapes and

completed, the electroformed part can

by h an d or any oth er m ean s: for exam pi e,

COSTS

re-entrant angles can be produced with a

then be electroplated, to combine the

intricate engravings can be reproduced

Tooling costs depend on the complexity

tend to produce a more precise coating

single mandrel.

cost effectiveness and strength of the

many times with electroforming.

of the mandrel Some mandrels are

thickness than faster ones.

and so there is less waste. However, plenty of hazardous chemicals are used in the process.These

Centrifugal Casting Process Central feed core

Runner Central system feed core

Die cavity

Solidified wall thickness

Open mold

Half

Forming Technology

Centrifugal Casting Spinning axis

Centrifugal casting is inexpensive and suitable for casting

INTRODUCTION Centrifugal casting covers a range

metals, plastics, composites and glass. Because tooling costs are very low, this process is used to prototype as well as mass

of spinning processes used to shape

spinning at high speed, the material is forced to flow through the mold cavities.

produce millions of parts.

The mold material - silicone or metal

Costs 1 • Low tooling costs 1 • Low unit costs, but depends on chosen 1 material

Typical Applications

Suitability

• Bathroom fittings • Jewelry • Prototyping and model making

• One-off to high volume production

Quality

Related Processes

Speed

• Very good reproduction of fine detail and surface texture

• Die casting • Investment casting • Sand casting

• Rapid cycle time (0.5-5 minutes typically)

Horizontal casting with multicavity tool

materials in their liquid state. By

Horizontal casting with single cavity tool

Vertical casting with open tool

TECHNICAL DESCRIPTION The tooling for centrifugal casting is either

the silicone to form the die cavity, or It can

Runners can be integrated Into the tooling to

silicone or machined metal. The former

be machined.

encourage air flow out of the die cavity.

- differentiates the 2 main types of

material is used to produce small and

centrifugal casting. Small parts,from

asymmetric parts. Metals are utilized to cast

shown above use tooling made from silicone

afew grams up to 1.5 kg {3.3 lb), can be

high melting temperature materials and

or metal. Molten material is fed along the

centrifugal casting the mold rotates around

cast in silicone molds.This technique

larger parts. Large molds can only produce

central feed core, which Is In the upright

a single axis, whereas rotation molding

is cost effective for producing any

parts that are rotationally symmetrical

position. As the mold spins the metal Is

tools are spun around 2 axes or more. In

quantity of small parts from one-off to

because of the nature of the spinning

forced along the runner system and info

operation, a skin of molten material forms

mass production because the molds are

process. Silicone tooling Is extremely cost

the die cavities. Flash forms between

over the inside surface of the mold to form

relatively inexpensive and are quick to

effective. The pattern can be pushed into

the meeting point of the 2 mold halves.

sheet or hollow geometries.

The 2 horizontal casting techniques

Vertical casting methods are similar to

rotation molding. The difference Is that in

make. Materials that can be cast include white metal, pewter, zinc and plastic. This technique is generally chosen for

RELATED PROCESSES

QUALITY

point materials (steel, aluminium

products that are symmetrical around

Regardless of the material used, this is a

and glass) are cast in metal molds.

an axis of rotation and can be i m (39.4

casting process and many comparable

Spinning the mold at high speed forces thematerial to flow through small die

in.) or more in diameter.The shape and

processes are available for shaping a

cavities. Surface details, complex shapes

complexity of part is limited by the

spectrum of material s: for example,

and thin wall sections are reproduced

nature of the process itself.

metal casting includes sand (page 120),

very well. In small parts tolerances of 250

die (page 124) and investment (page 130)

microns (0.00984 in.) are realistic.

Larger products and higher melting

Composites and powders are also

The fact that centrifugal casting is a

formed in metal molds.This technique

techniques. Comparable shapes can be

is similar to rotation molding (page 36), except that the mold is spun around only

formed in plastic by injection molding

low pressure process has benefits and

(page 50), vacuum casting (page 40) and reaction injection molding (page

limitations for the material quality. For

64). Also, similar glassware can be

the die cavity-as in injection molding

TYPICAL APPLICATIONS

made by press molding (page 176) and

and pressure die casting - so the parts

Silicone molds are used to produce

glassblowing (page 152). The quality that differentiates

therefore tends to be used for parts that

parts for a range of industries.The largest

centrifugal casting from all these

do not have to withstand high loads.

areas of application are for jewelry,

processes is that it combines relatively

However, the benefit of low pressures is

bathroom fittings and architectural

low costs for small parts in materials

that there is less distortion as the part

models.These products are within the

with a melting point below 5000C

cools and shrinks.

size limitations of silicone tooling and

(9320F).The tooling costs for larger parts

Large metal parts that are formed

the low melting point metals are also

and higher melting point materials can

centrifugally have a harder outer surface

sufficiently strong for centrifugal casting.

be relatively small, too, because it is a low

because a higher concentration of

pressure process.

heavier molecules will be forced to the

i axis,instead of 2 axes ormore.

prototypes, models and mass production

Metal molds are used to cast metal pressure vessels,flywheels, pipes and glass tableware.

example, materials are not packed into

will be more porous.This process

periphery of the die cavity.

while in metal molds wall thicknesses can be much larger. Metals produced in silicone mold

centrifugal casting have a low melting point. Therefore, they will not be as

Case Study

Centrifugal casting a pewter scale model This cast pewter part is quite large (image

the flash metal can be collected. The mold is

strong and resilient as metals formed

very hot and so it is set to 1 side and allowed

1) and so each mold can produce only 1 part

spun at high speed. Molten pewter is poured

to cool. From molten to solid state it will

in other ways.To overcome this problem

at a time. The silicone mold is assembled

into the central feed core at more than 4500C

shrink approximately 6%. Centrifugal casting

wall thickness can be increased and ribs

with cores (image 2}. These make it possible

(84O0F) (image 5) and enters the mold, where

is a low pressure process, so the part is less

likely to distort as it cools.

added to the part.

to form re-entrant angles. The 2 halves of

it is pushed through the runner system by

the mold are brought together and located

centrifugal force. It begins to cool and solidify

COMPATIBLE MATERIALS

with pimples and matching recesses on the

very quickly. Once the mold is full of metal the

Silicone molds can be used to cast some

interface (image 3).

plastics including polyurethane. Metals include white metal, pewter and zinc. Metal molds are used to shape most

The mold is placed onto a spinning table

spinning is stopped and the pewter is allowed to rest for 3 minutes.

and clamped between 2 metal discs (image 4),

The mold halves are separated and the

It is sealed into a box during spinning so that

cast metal part is removed (image 6). It is still

other metals, powders (metal, plastic, ceramic and glass) and metal matrix composites.

COSTS Silicone tooling costs are very low,

especially for multiple cavity molds. Metal molds are more expensive, but still relatively inexpensive for their size.

The cycle time for low melting point metals and plastics ranges from 0.5 Top Really small parts, such as this 40:1 scale oil

which is part of a model Raleigh car, displays

to 5 minutes. Glass products can take many days to anneal, depending on the

very fine detailing.

thickness of material. Labour costs are

can for a model railway,

are feasible with

Right

centrifugal casting.

Above

This multi-cavity silicone split mold produces 35 metal parts

A un scale model of an

in a single cycle.

generally low.

ENVIRONMENTAL IMPACTS All scrap metal, thermoplastics and glass

alloy wheel in pewter.

can be directly recycled. Small parts require very little energy to produce,

DESIGN OPPORTUNITIES

Because centrifugal casting is a

while multicavity molds are cost effective

The main opportunities for designers are

low-pressure process, step changes in

and reduce material consumption.

associated with silicone mold centrifugal

wall thickness do not cause significant

casting.This technique can produce from

problems. Also, parts can be fed with

White metal and pewter are alloys of lead.The exception to this rule is British

i to 100 parts in a single cycle.

molten material from multiple points to

Standard pewter, which contains no lead.

Large parts are cast around the central core. Separate gates feed small parts, which are placed around the central coTe,

overcome small wall sections in between

Even though it is a naturally occurring

larger sections.

material, in large enough quantities

As with other metal casting

lead is a pollutant: for example, it causes problems with the nervous system

so many can be cast in a single mold (see

techniques, metal parts can be molded

image, right).

with inserts and removable cores. Parts

if ingested in sufficient quantities.

can also be polished, electroplated,

Therefore, lead should not be used in

painted and powder coated.

products designed for drinking or eating.

Using semi-rigid silicone means complex details and re-entTant angles

that are not suitable in hard tooling can be cast. Multiple cores can be Inserted by

DESIGN CONSIDERATIONS

hand for shapes that even silicone will

In silicone molds wall thickness ranges

CMA Moldform

not tolerate.

from 0.25 mm to 12 mm (0.01-0.472 in.),

www.cmamoldform.co.uk

Featured Manufacturer

Press Braking Process

Hydraulic ram

Forming Technology

Press Braking This simple and versatile technique is utilized to bend sheet

INTRODUCTION

Workpiece

[blank]

Press brakes are fundamental to low

metal profiles for prototypes and batch production. A range of geometries can be formed including bend, continuous and sheet,

to medium volume metalwork.When

t

¦>i4

combined with cutting and joining Die I

equipment, press brakes are capable of producing a range of products including

it is also referred to as brake forming.

Stage 1: Load

continuous, bend and sheet geometries.

Bottom bending

Stage 2: Air bending

Gooseneck bending

They tend to be manually operated and Costs • No cost for standard tooling • Low to moderate unit costs

Typical Applications

Suitability

• Consumer electronics and appliances • Packaging • Transport and automotive

• One-off to batch production

are used for one-off, low volume and batch production up to 5,000 units. Pressure is applied by a hydraulic ram, which forces the metal to bend along a single axis between a punch and die.

Quality • High quality and accurate bends to within ±0.1 mm (0.004 in.)

Related Processes • Extrusion • Metal stamping • Roll forming

Speed • Cycle time of up to 6 bends per minute • Machine set-up time can be long

There are many standard punches and dies, which are used to produce a range

TECHNICAL DESCRIPTION Press brakes are driven by hydraulic rams,

tonnage required to make the form. A typical

which apply vertical pressure. The tonnage

press brake of 100 tonnes (110.2 US tons)

the type of punch and die that are used;

required is determined by U factors: bend

will fold 3 m 110 ft) of 5 mm (0.2 in.) steel in a

there are many different types, including

length, thickness, tensile strength and bend

32 mm (1.26 in.) wide lower die. A narrower

air bending dies, V-dies for bottom bending,

radii. Increasing the width of the lower die

die will require more tonnage.

gooseneck dies, acute angle dies and

increases the bend radii and reduces the

loaded onto the die. In stage 2, pressure

of bends with different angles and

is applied by the hydraulic ram so the

circumferences (see image, opposite),but always in a straight line.

TYPICAL APPLICATIONS Press brakes are versatile machines,

capable of bending both thick and thin sections up to 16 m (52 ft) long. Examples include lorry sidings, architectural metalwork, interiors, kitchens, furniture

In stage 1, the prepared workpiece is

Metal stamping (page 82) can produce shapes with complex undulating profiles in a single operation. Design for this process is very different from that of press braking.

Metal folding is similar to press

punch forces the part to bend. Each bend

structural metalwork and repairs.

into a sheet metalworking production

RELATED PROCESSES

thin walled metal enclosures, packaging

bottom bending with matched dies (also

between bends. Alternatively, the same

for high precision metalwork because it

bend can be made on a batch of parts

needs more pressure to operate.Gooseneck

before the machine is repositioned for

dies are for bending re-entrant angles that

the next operation.

cannot be accessed by a conventional tool.

Right Many different shapes of bend can be formed

volumes less than 5,000 parts. Each bend is another operation andthe machine

include squares, rectangles, pentagons,

has to be set up to accommodate

each bend. While this is not a lengthy process with modern computer-guided machinery, every second counts in high volume production.Thus large volumes of manufacture often justify processes

with highertooling costs provided they reduce the number of operations and cycle time.

without investment in tooling, using standard

and electronics housing, for example. The sorts of geometries that can be made hexagons and tapered shapes.

punches like these.

QUALITY

Roll forming (page 110) shapes

Applying a bend to a sheet of material

metal sheet into continuous profiles

increases its strength, while bending

with a constant wall section and is

processes combine the ductility and

similar to extrusion. Roll forming has

strength of metals to produce parts with

the advantage of being able to process

improved rigidity and lightness.

almost any metal. Extrusion, on the other hand, is capable of producing hollow profiles with varying wall thicknesses.

Air bending is used for most general work such as precision metalwork, while

called V-die bending or coining) is reserved

line.They are used in the manufacture of

This process tends to be limited to

improved durability.

guided machines reposition themselves

bends in thin sheet materials. Metal

and lighting, prototypes and general

rotary dies. Tools can be laser hardened for

takes only a few seconds. Computer-

braking: they are both used to form tight folding machines are often integrated

The geometry of the bend determines

Machines are computer guided, which means they are precise to within at least o.oi mm (0.0004 in-) and can be preprogrammed for any given part.

Even so, the aesthetic quality of press

Case Study

braking is largely dependent on the skill of the operator and their experience with

Press braking an aluminium enclosure

that particular machine, Aluminium blanks are prepared for press

In air bending with standard tooling, the

conventional punch because of the length

DESIGN OPPORTUNITIES

braking by turret punching (page 260) and

metal blank is inserted against a computer-

Press brakes form continuous bends in

deburring, guillotining or laser cutting (page

guided stop (image 2), which ensures that the

sheet material up to 8 m (26 ft) long; 16 m (52 ft) is possible by literally bolting

248). In this case study, the 3 mm (0.118 in.)

part is located precisely prior to bending. The

a way that the punch can access the joint

aluminium blanks were cut out using a turret

downstroke of the punch is smooth to avoid

line as easily as possible and so that bends

machines together. Using an air bending

punch. As much of the preparatory work as

stressing the material unnecessarily and

do not run too dose to the edge (image 10).

die, it is possible to bend a range of

possible is carried out before the bending

takes only a couple of seconds (image 3). The

Bends that run off at an angle, for example,

angles very quickly by depressing the ram

process is done, because this is quicker and

process is repeated to form the second go0

may have to be formed in matched dies to

easier on a flat sheet.

bend (images 4 and 5).

maintain accuracy.

only as much as necessary. Acute-angle

The blanks are processed in batches

dies can form sheet material into acute bends down to 30°, Segmented dies can

produce bends up to specific lengths,

Gooseneck bending (images 6 and 7) is

of the overhang.

The formed joints are designed in a such

Finally the joints are TIG welded, ground

(image 1) so the factory can supply its

used when it would not be possible to form

and polished in preparations for spray

customers just-in-time (JIT).

the second bend (images 8 and 9) with a

painting (images 11 and 12).

which means multiple bends can be made simultaneously.

Press brakes have the capability of producing long, tapered and segmented

profiles, which are not possible with roll forming or extrusion.

DESIGN CONSIDERATIONS The main limitation of press braking is that it can do only straight line bends. The internal radius is roughly 1 times

is cold formed. Beyond this, the surface

tooling will increase the unit price,

material thickness for ductile material and 3 times material thickness for

of the material reaches the extent of its

depending on the size and complexity

ductility and will tear. Introducing heat

of the bend.

hard materials. Bend allowance (also

to the bend area means the process

Cycle time is up to 6 bends per minute

referred to as stretch allowance) is

can bend higher thicknesses and the

used to calculate the dimensions of a

limitation is then machine capability.

Set-up can take a long time but is greatly

piece of metal post-forming. Generally,

Maximum dimensions are generally

reduced by a skilled operator.

it is sufficient to add the length of arc through the middle of the material

limited by sheet size because lengths up to 16 m (52 ft) have been bent for street

operations because a high level of skill

thickness to calculate the dimensions

lighting, for example.

and experience are required to produce

on modern computer guided equipment.

Labour costs are high for manual

accurate parts.

of the flat net shape.

COMPATIBLE MATERIALS

The punch has to apply pressure along the entire length of the bend. Hollow

Almost all metals can be formed

parts are produced by fabricating sheet

using press braking, including steel,

Bending is an efficient use of materials

geometries post-bending.This is also a

aluminium, copper and titanium. Ductile

and energy.There is no scrap in the

consideration for enclosures with 2 close

metals will bend more easily and so

bending operation, although there may

90° angle bends that form an undercut

thicker sections can be formed.

be scrap produced in the preparation

Punches with overhanging features can

COSTS

subsequent finishing operations.

be used; they reach into undercuts and

Standard tooling is used to produce

apply pressure along the entire length of

a wide range of bent geometries: for

the bend.

example, an air bending die can produce

(of the metal blank, for example) and in

feature (re-entrant), for example.

The maximum thickness (subject

ENVIRONMENTAL IMPACTS

arange of angles down to very acute

to the capability of the machine) is

bends. However, this is less accurate than

approximately 50 mm (2 in.) if the metal

V-dies for bottom bending. Specialized

Featured Manufacturer Cove Industries www.cove-industries.co.uk

TECHNICAL DESCRIPTION

Studio Glassblowing Process

There are many stages to glassblowing by

Air blown in Blowing iron

hand, and everything that is needed for this process must be prepared in advance in order not to waste time and fuel because

Forming Technology

glassblowing is carried out at temperatures

Glassblowing

Cracked off

in excess of 600°C (1112°F). The glass used in studio glassblowing is typically soda lime or crystal glass. It is

Both decorative and functional, hollow and open-ended vessels can be created by glassblowing. The process involves blowing

INTRODUCTION Glassblowing has been used to create a

multitude of household and industrial

maintained at more than 1120°C (2(K8°F) in a crucible, which is accessible through a small hole in the side of the furnace. It is only cooled down when the crucible needs

a bubble of air inside a mass of molten glass, which is either

products for centuries. However, many

to be removed and replenished, which is

of the blown glass products that we

gathered on the end of a blowing iron or pressed into a mold.

approximately every 18 months. The surface

use today are manufactured in 2 ways.

of the glass can develop a skin over time;

Th e fi rst m eth od i s "kn 0wn as 'studio

this is periodically skimmed off.

glass' and is the production of one-off Costs • High tooling costs for mechanized production, low for studio glassblowing • Unit cost for mechanized production is low

Quality • High quality and high perceived value

Typical Applications • Food and beverage packaging • Pharmaceutical packaging • Tableware and cookware

Related Processes • Glass press molding • Plastic blow molding • Water jet cutting and scoring

Suitability • One-off to high volume production

Speed • Fast cycle time if mechanized • Slow to very slow cycle time for studio glassblowing

In stage 1, the nose of the blowing

Stage 1

Stage 2

Stage 3

Stage U

Stage 5

Stage 6

Stage 7 Finished container

glass at a working temperature because if

way. In stage 3, profiled formers or molds

the glass cools below 600°C (1112°F) and is

may be used to shape the glass accurately.

pieces, generally with artistic expression.

iron is preheated in a small kiln, raising

The second method is mechanized

its temperature to above 600oC (1112°F).

reheated it may suffer thermal shock, which

In stage 4, pucellas (sprung metal tongsj

production and can be divided into 2

Once it is glowing red hot a small piece of

will cause it to shatter.

are used to reduce the diameter of the glass

main categories: machine press and

coloured glass is attached to the blowing

press; and machine press and blow.

end. The coloured glass and nose of the

decorated in many ways. Coloured glass and

shaping of the glass and to achieve straight-

blowing iron are dipped into the crucible of

silver foils can be rolled onto the surface and

sided vessels, for example.

molten glass at between 30° and ^5°. Molten

then encapsulated into the part with another

glass is gathered onto the end of the blowing

layer of clear glass. Coloured threads of

onto a punting iron, or 'punty'. This is a

iron by making up to 4 full turns so that even

glass can be trailed over the surface of the

steel rod with a small glass gather, which

coverage is achieved. The blowing iron must

parison from a separate gather. These trails

is attached to the base of the workpiece

now be constantly turned for the duration

can be dragged over the surface of the glass

by an assistant guided by the glassmaker.

of the process to prevent the glass from

to create patterns, in a technique known as

In stage 5, the glass vessel is 'cracked off

slumping.

'feathering'.

the blowing Iron and in stages 6 and 7 it is

Mouth glassblowing has been practised for over 20 centuries. Before the development of blowing irons, hollow containers were made using friable cores that could be scraped out once the glass

had solidified. High volume mechanized production uses compressed air to blow molten glass into cooled molds, which greatly accelerates the rate of production.

The parison of hot glass is rolled on a

The molten glass can be marked and

Many tools are needed to shape the hot

vessel. Formers are utilized to control the

In stage 4, the workpiece is transferred

shaped from the open end. The finished part

'marvering' table, which has a polished

glass when it is being blown. Blocks of wood

Is placed in an annealing kiln. Annealing

metal surface. The process of 'marvering'

and paper are used to prepare the parison

is the process of cooling glass down over a

TYPICAL APPLICATIONS

begins the shaping of the glass. In stage

and shape the glass. The blocks of wood are

prolonged period. This is essential because

Glassblowing is suitable for a variety of

2, air is blown in and it is intermittently

kept submerged in water so that they do not

stress build-up occurs in glass of varying

vessels, containers and bottles, which

inserted into the 'gloryhole' to maintain its

catch fire when they are held directly against

thickness as it cools at different rates and

include tableware, cookware, food and

temperature above 600°C (1112°F). This is

the surface of the glass. Paper pads are

this can result in shattering. The annealing

pharmaceutical packaging, storage

a gas-fired chamber that is used to keep the

sprinkled with water and used in the same

process gradually relieves these stresses.

scoring (page 276) are used to profile

the raw material. Surface imperfections

exciting effects. A method called'graal'

sheet materials.

can be minimized by tempering, and

is used to create sophisticated patterns

jars and tumblers. Glassware is ideal

for applications that require chemical resistance and hygienic qualities.

RELATED PROCESSES Many items of packaging that were

QUALITY

previously made in glass are now

Glass is a material that has a high

producedbyblowmolding plastic (page

perceived value because it combines

22).This process is used to manufacture

decorative qualities with great inherent

careful mixing and heating of batch

and textures on the surface of glass

glass with cullet (recyclate) will ensure the highest quality of finished product.

by etching into a layer of colour on the surface of a blown and cooled parison, which is then reheated and coated in

DESIGN OPPORTUNITIES

another layer of glass to form the final

domestic, pharmaceutical, agricultural

strength. Certain glass materials can

Because the studio glass processes

product. It is possible to create a layer of

and industrial containers. Glass press

withstand intense heating and cooling,

are free from the limitations of mass

cracks in the surface of glass by dipping

molding (page 176) is used to produce

and sudden temperature changes.

production, there are many ways that

ahot parison into warm water and then

glassmakers can manipulate the shape

reheating it.The effect of the water is to

and surface of the glass to create

cover the surface with cracks. Air bubbles

open-mouthed and sheet geometries,

The structure is weakened only by

while water jet cutting (page 272) and

surface imperfections and impurities in

Case Study

Studio glassblowing into a mold The glass vessel being made here was

All the time the studio glassblower is rolling

designed by Peter Furlonger in 2005 and

the hot glass back and forth on the blowing

and 6oo°C (932-1112^) in a small kiln.The

is being blown by the studio team at The

iron. This ensures that the glass does not

blown glass parison is placed in the mold,

National Glass Centre.

slump and deform.

rotated and blown simultaneously forcing it

The blowing iron is preheated until it is

The hot glass parison is then laid into a

The mold is preheated to between 500°C

against the relatively cooler mold walls, which

glowing red, around 5oo0C (iii20F).Then a

dish of blue powdered glass (image 5). Layers

lump of coloured glass is attached to the end

of colour are built up in this way to create

glass cools down and loses its red glow. The

of the blowing iron (image 1). It is brought up

added'depth'in the abrasive blasted finish,

glassblower then uses a blowtorch to produce

to working temperature in a 'gloryhole' and

which is applied later (page 388).

a metallic effect on the outside of the vessel

'marvered' on a polished steel table (image 2).

The coloured glass is then dipped into a

The gloryhole is used to maintain the temperature of the glass at above 6oo0C

starts to harden the glass (image 9).The

(image 10).This effect will be used to enhance the effects of abrasive blasting.

crucible of molten glass in a furnace, which

(ni20F) and around 8oo0C (i4720F) (image 6),

is maintained at more than 1120C (20480F),

where it feels like sticky toffee, and can be

to size by'cracking-off'the top (image 11).

and an even coating of clear glass is gathered

easily shaped and worked (image 7).

The final blown vessel (image 12) is annealed

over the coloured glass (image 3). The hot

The glass parison is blown and heated

glass is shaped into a parison using cherry

and shaped until it is a suitable size with

wood formers that have been soaked in water

adequate wall thickness for molding

(image 4). This process is repeated several times

The parison is in its final shape. It Is cut

before it is finished with abrasive blasting.

(image 8). During blowing the temperature of the glass must be above 6oo0C (in20F) so

until there is plenty of glass on the end of the

that it can be manipulated: any colder and it

blowing iron for the next stage of the process.

will become too rigid.

can be encapsulated in the walls of

DESIGN CONSIDERATIONS

high tooling costs and set-up time mean

a glass vessel by pricking the molten parison with pins andthen sealing the small bubbles of air in with another

Studio glassblowing is limited in size onlyby the dimensions ofthe'gloryhole'

that this process is suitable only for runs

layer of glass. Coloured glass can be

This process is nearly always carried out

about stress concentrations in the final

trailed across the surface of the parison,

by 2 people and so can be expensive. A

product. Smoothing out the shape as

or coloured glass pieces can be rolled

typical blown part can be made in 20

much as possible will reduce stress,

onto the surface to create controlled and

minutes or so, while more complex and

although tight radii can be achieved

beautiful patterns. Mechanized methods are used only for mass production. Very precise detail

and what the glassmaker can handle.

Designers must be very considerate

sophisticated techniques will increase

where necessary. Problems may occur

the operation times dramatically. The

in screw cap features, for example.

experience of the maker, however, will

Designers generally work to draft angles of 5° but this is not a problem when working with round and elliptical

can be achieved such as screw threads

limit the effects that can be achieved and

and embossed logos.The tolerances are

the rate of production.

fine and repeatability is good.

of at least 10,000 parts.

Products for mass production

shapes. It is advised that parts are

glassblowing have to be designed to

kept symmetrical and that the neck is

accommodate the production line.The

centralized because the product has to fit

Case Study

Studio glassblowing with coloured effects mass of glass is wound around a punty, which

coils the glass and transfers the spiralling

of the glass is also maintained throughout

glass. This is a relatively simple piece designed

pattern from longitudinal to helix (image

the entire process, at more than 8oo0C

by him and blown by Layne Rowe; it shows

5). The mixed colour parison Is worked on a

(i4720F) in a 'gloryhole' (image 10).

some of the weaith of techniques used by the

marvering tabie and cherry wood formers are

London Glassblowing studio team.

used to create a uniform and stable shape.

The spiralling pattern within the glass can

on the punty enables the glassblower to

now been seen (image 6). The glass parison,

develop the shape further; by forming,

A small piece of white glass is attached to the

which has now been transferred to a blowing

pulling a stem or flattening it on a cork table,

end of a punty together with a 'gob' of clear

iron, is dipped into the crucible in the furnace

for example. In this case the glassblower is

glass (image 2). The white giass is heated

and a'gather'of clear glass forms a coating

making a bowl and so needs to expand the

to around 8oo0C (i4720F) and is worked on

over the pattern, which is worked in a wood

diameter of the rim. This is achieved with

a 'marver'table into a long thin rod. At this

block or former (image 7),

pucellas, which are used to draw out the hot

point a gob of molten red and clear glass is

in and out of the gloryhole to maintain the

over the white glass (image 3). Overlaying

glass on the end of the blowing iron to start

required working temperature. Once the

coloured glass builds up strata that add visual

blowing (image 8). The blowing process

bowl is finished, he cracks it off the end of the

depth to the final piece.

expands the gob of glass, magnifying the

punty and it is transferred to an annealing

pattern as it does so. While the parison is

kiln for controlled cooling over a period of 36

marvering table and then swung, which

blown it is continuously rotated and worked

hours (image 13).

exploits gravity to elongate it. A thin stream

with damp paper pads to coax the glass into

of molten blue glass is then trailed across (image 4). At this stage it is difficult to differentiate the colours, as they are all glowing red hot. At this point, the glass gob comprises a white core, with overlaid red and clear

glass and a trailed blue spiral. To enhance the pattern even further, the molten

Tooling costs are high for mechanized production methods, but are low to non¬

COMPATIBLE MATERIALS

existent for studio glassblowing, where

Soda-lime glass is the most commonly

equipment costs are low. For different

used for high-volume production, it

products, studio glassblowing often

is made up of silica sand, soda ash,

utilizes the same tools, which include

limestone and other additives. Light

metal tongs, paper formers, cherry wood

shades, tableware, cut glass, crystal glass

paddles and cork tables.

and decorative objects are typically made

Cycle time is governed by the

from lead alkali glass. Borosilicate glass

preparation and annealing required in

is used for laboratory equipment, high temperature lighting applications and

glass production. Mechanized molding

cookware.

Clark produce in excess of 15,000 glass

cycles are extremely fast. Beatson containers every 24hours (see case study,

Featured Manufacturer

London Glassblowing www.londonglassblowing.co.uk

page 159). Studio glass, on the other hand.

glass (image 12). All the time he 1s moving it

repeated 2 or 3 times, until there Is sufficient

the surface of the overlaid gob In a spiral

labelling lines.

The process of gathering and forming is

gathered onto a punty and allowed to run

The overlaid glass is worked on the

COSTS

Once blowing is complete, the parison is transferred onto a punty (image 11). Working

preheated in a small gas-fired kiln (image 1).

The 'punty' and biowing irons are

into conventional production,filling and

the desired shape (image 9). The temperature

Peter Layton is renowned for his use of colour

to produce dynamic and engaging works in

o CO CD (X)

Machine Glassblowing Process

is a much slower process that requires

Machine blow and blow method

great skill and experience. Each product could take between 5 minutes and 2

Stage 3

of stages required.

Stage U

Stage 5

mechanized methods and are relatively

main raw ingredient, silica sand, comprises

dispense them on a conveyor belt that

higher in studio glass, due to the high

about 70% of the final product and is piled

transfers the hot glass products (5500C/

level of craftsmanship needed,

up inside the factory (irnage 1). The various

io220F) to a gas-fired lehrfor annealing.

ENVIRONMENTAL IMPACTS ideal for packaging that will be refilled, especially for food an d beverag es, which greatly extends a product's useful life. Successful refilling systems, such as the

Finnish drinks bottles and British milk bottles, are refilled tens of times before Stage 3

Stage 5

Finished Stage 6 container

they need to be recycled. All scrap glass material can be

TECHNICAL DESCRIPTION The mechanized glassblowing process

injected through the mold into the formed

begins in the mixing department, where

neck. In the press and blow method, all

the raw materials are mixed together.

of this is done by a plunger. In stage U,

is injected through the neck to blow the

so there have been many developments

to form a homogenous, molten mass.

vessel into its final shape. The glass cools

in recent years to reduce energy

Glass is drawn through the furnace and

against the sides of the mold before it

consumption. Improved furnace design

opens and releases the part. The vessels

and production techniques reduce energy usage and thus reduce the price

(2100°F|. This process takes up to 24

surface treatment process to apply an

ofproduction.The raw ingredients

hours.

external coating, which helps the glass

of glass can affect its environmental

maintain its strength during its working

credentials because they are mainly

life. The vessels are fed by conveyor belt

oxides, which will find their way into the

through the annealing lehr to remove

atmosphere during production.

is then subject to rigorous inspections,

pressed or blown. The press and blow

including sidewall and base scans,

method is more suited to wide-mouth jars,

pressure tests, bore tests and the flatness

whereas the blow and blow technique is

of the sealing surface.

Robotic arms invert the parisons through

cn (T) cd

180° as the freshly blown bottles are

z:

cd

Glassblowing is energy intensive and

are then passed through a 'hot end'

that the parison (pre-form) Is either

O

the blowing mold (image 4) in tandem.

landfill every year in the UK alone.

conditioned (slowly cooled) to its working

lehr to improve the product's resistance to

and the neck is formed. These formed

parisons (image 3) are then transferred to

tonnes of container glass still make it to

temperature of approximately 1150°C

scratching and scuffing. Every container

and are fed into an automated packaging machine (image 9).

molds, into which the molten glass settles

the surface of the cool mold (image 6).

1500°C (2730°F) where they fuse together

processes are essentially the same, except

The gobs are fed along tracks to the

degradation. Even so, more than 1 million

to the second blow mold. In stage 6, air

treatment is added at the 'cold end' of the

forehearth and is cut into 'gobs' (image 2).

remanufactured many times without

the glass-melting furnace with cutlet at

press and blow or blow and blow. The

the production line as a single stream

air, which forces the molten glass onto

180°. In stage 5, the bottle is transferred

molding methods that are used, either

areas (image 8). The finished bottles leave

glass flows from the bottom of the

recycling because it can be melted and

to make clear glass. They are fed into

any stress build-up. A second surface

the glass-melting furnace the conditioned

and the bottles are filled with compressed

the mold opens and a partially formed

machine below. There are 2 different

are moved towards testing and inspection

removed (image 5). The split mold closes

vessel is released and inverted through

'gobs'. These are fed into a bottle-making

Having left the lehr, the bank of bottles

molten glass, and after sufficient time in

recycled directly in the manufacturing

with additives, or a decolourant is added

bottom of the forehearth and is cut into

continuously all year round (image 7) and

ingredients are mixed and melted to form

process. Glass is an ideal material for

At this stage they are either coloured

The conditioned glass flows from the

All 16 blowing molds produce bottles

made using the blow and blow method. The

Glass is along-lasting.material. It is

| Gob

A 500 ml (0.88 pint) beer bottle can be

Labour costs are relatively low for

Finished Stage 6 bottle

Machine press and blow method

Stage 1 Stage 2

Mechanized glassblowing a beer bottle

hours to blow, depending on the number

T Stage 1 Stage 2

Case Study

used for containers with a narrower neck. In stage 1, the molten glass gob is guided along tracks into a parison mold.

In stage 2 of the blow and blow method, a plunger rises and presses a neck into the molten glass, and in stage 3, air is

Featured Manufacturer Beatson Clark www.beatsonclark.co.uk

Lampworking Operations Workpiece: sealed glass tube

Localized heating . upto 1000oC

Localized heating up

Blowing

Hole boring (18320FI

to 1000oC (18320F)

Forming Technology

Lampworking

Rubber bung Air blown in by lampworker

Glass is formed into hollow shapes and vessels by lampworking, also known as 'flameworking', by a combination of intense heat and manipulation by a skilled lampworker. Products range from

Stage 2: Forming

INTRODUCTION Hot glass forms easily

The process of lampworking has been

Cold glass remains unchanged

around since the development of the Bunsen burner around 150 years ago. It is currently used to shape glass into

jewelry to complex scientific laboratory equipment.

functional and decorative objects.

Localized heating up

to 1000oC (18320Fl

Bending

Mandrel forming

Workpiece: glass tube

Cooling glass maintains shape Mandrel rotated

Thisis ahotforming process: borosilicate glass is formed at 800-

• Typically no tooling costs • Moderate to high unit costs

Typical Applications

Suitability

i2000C (i472-2i920F) and soda-lime

• Artwork • Jewelry • Laboratory equipment

• One-off to batch production

glass is formed at 500-700^

Workpiece glass tube or rod gradually heated up to working temperature

(g32-i2920F). A great deal of skill and experience are required to work hot glass

Quality

Related Processes

Speed

• Very high quality, but depends on the skill of the lampworker

Glass press molding • Glassblowing

• Moderate to long cycle time, depending on the size and complexity of part

intimately, and therefore this is one of

the few industries that still

Cold glass remains unchanged

trains apprentice workers. Applied pressure

Hot glass forms easily Stage 2: Forming

Lampworking is carried out in i of 2 ways: benchwork or lathework.

TECHNICAL DESCRIPTION

Benchwork can be used to create

Although benchworking and latheworking

complex, intricate and asymmetric

are carried out in different ways, they

if needed. The tools used are similar to

shapes, whereas lathework is suitable

use the same basic techniques such

those for glassblowing; various formers

for parts that are symmetrical around an

as blowing, bending, hole boring and

shape the workpiece and 'marver' the hot

axis of rotation (or at least partly so).

mandrel forming.

glass. Tungsten tweezers are used to pull

Benchwork is generally limited to 30 mm (1.18 in.) diameter tube; it is

impractical for the lampworker to hold anything larger and manipulate it at the same time. Latheworking is suitable formuch largertube diameters (upto 415 mm/16.34 in.).

A mixture of natural gas and oxygen

desired shape - with very fine tolerances

glass across a surface or to bore holes.

are burnt to generate the heat required

Trails of coloured glass can be pulled

for lampworking. Alternatively, propane

across the surface or metal leaf feathered

is used instead of natural gas, but it

onto the hot glass.

burns much hotter and so reduces the

Everything made in this way has to be

temperature range at which the glass

annealed in a kiln. For borosilicate glass

can be formed. The working temperature

the temperature of the kiln is brought

is 800-1200°C |U72-21920F| for

up to approximately 570°C (1058°F) and

borosilicate glass, at which stage it has

then maintained for 20 minutes, after

TYPICAL APPLICATIONS

the flexibility of softened chewing gum.

which it is slowly cooled down to room

Lampworking is the only way to make

All parts of the workpiece must be kept at

temperature. This process is essential to

certain specialized scientific apparatus

a similar temperature to avoid cracking.

andprecision glassware.When combined

with casting and grinding, lampworking

The workpiece can then be rolled,

blown, twisted, bent or shaped into the

relieve built up stress within the glass. Some very large pieces, such as artworks, can takes several weeks to anneal.

2 "D

s

o

aj

Case Study

Benchworking a total condensation stillhead A total condensation stillhead (variable

twist and seal the end of the glass tube

the previously formed part. Once in place,

takeoff pattern) is a piece of scientific

(image 3). From the cool end, air is then blown

the 2 parts are heated simultaneously, which

apparatus used for a specific distillation

into the part, forcing the hot end of the tube

causes the glass to fuse and join (image

process. This case study demonstrates some

into an even bubble (image 4). At each stage

11). A tight bend is achieved at the neck by

of the techniques used to produce it. Like any

of the process the accuracy of the parts are

blowing into the tube - air pressure acts like

other lampworking, a stillhead starts as a

checked against the drawing (image 5).

series of glass tubes that are cut to length in preparation for the flamework itself. The lampworker uses a technical drawing

a mandrel, which stops the walls collapsing

The blown tube is placed back into the

- and by forming the bend by hand (image 12).

flame and tungsten picks are used to form

This relatively simple subassembly (image 13)

a hole (image 6), which is opened out with a

will form only a small section of the stillhead.

(BS 308) to ensure that the product is to be

tungsten reamer (image 7). In the meantime

constructed to close tolerances (image 1).

the second part of the stillhead is brought

The first part of the stillhead is brought up

up to temperature (image 8) and drawn out

to working temperature and starts to glow

without reducing the wall thickness (image

cherry red (image 2). When hot enough the

9). It is heated around its circumference and

glass can be pulled and manipulated like

the hot glass is pushed back on itself to create

chewing gum. Tungsten picks are used to

a rib (image 10). This will help to locate it in

is used to produce everything from test tubes to complex process glassware.

Many industries utilize the versatility of lampworking in glass for prototyping and plant equipment. It is also used in

the jewelry industry to make beads and other decorative pieces. Architects and

artists alike have applied this process to lighting, sculptures andfunctional parts of their designs.

forming, cutting and joining action. Even tiny stresses in the part will cause the

RELATED PROCESSES

glass to shatter or crack. Annealing the

Lampworking needs a great deal of

parts after lampworking ensures they

skill; even simple shapes can be time-

are stabilized and stress free.

consuming to produce. Geometries that

are suitable for glassblowing (page 152)

DESIGN OPPORTUNITIES

or press molding (page 176) will therefore

The size, geometry and complexity of a

be made in that way as soon as the

part are limited only by the imagination

volumes justifythetooling costs.

of the designer. Lampworking is equally

3

suitable for precise functional objects

QUALITY

and decorative fluid artefacts.

The quality of the part is largely dependent on the skill of the lampworker.

DESIGN CONSIDERATIONS

During operation, the parts have to be

Everything made in this way comes from

carefully heated and cooled for each

a combination oftube and rod glass. 4

JdV ¦pj

to temperature it is carefully bent by hand

it out and into the profile that will neatly fit

coated mandrel. The glass must reach its

(image 16) to form the final bend (image 17).

the hole (images 21 and 22). The 2 parts are

optimum temperature just before it is formed

J 1

A glass spiral Is created using a graphite-

M

the other hand, can be found in domestic

suitable for automation. Where possible,

expansion (COE) to be compatible. COE is the rate at which the glass molecules

applications such as packaging, bottles,

glassblowing and press molding are

windows and lighting. It is known as 'soft

used to produce standard parts that are

expand and contract during the heating

glass', because it has a lower melting

finished or assembled with lampworking,

and cooling process. A part made up of

temperature. Soda-lime glass is less

to reduce cycle time andlabour costs.

glass with different COE values will crack

expensive; unlike borosilicate, however,

or shatter because of the build-up of

it cannot be mended or reformed once

stress within the material.

it has been annealed. One of the most

Glass scrap is recycled by the supplier, so

common artistic glasses is Morettl Glass,

no glass is wasted during the process.

The various ranges of glass are

idiosyncratic; they have different colour

manufactured in Murano, Italy.

fuses (images 23 and 24). A complete stillhead

complete, so assembly can start.This process

stretch rather than bend. Such an operation

comprises heating and boring holes and then

(image 25) takes 4,A hours to create from start

requires a great deal of skill and experience.

joining the parts together with a flame. To

to finish.

The glass tube may sag very slightly just

do this, a very small area is heated (image 18)

before it is formed over the mandrel

and then blown, forcing the glass to stretch

(image 14).

until it can be removed with the tungsten picks.The hole is opened out to the correct

section, using a much larger area of heat

diameter with a tungsten reamer (image

(image 15). Spreading the heat out makes

19). The extension that will be joined to the

sure that the U-bend will be even across a

assembly is prepared by cutting it to length

large diameter. As soon as the glass is up

with the flame (image 20) and then opening

20

21

22

23

ENVIRONMENTAL IMPACTS

A great deal of heat is required to bring the glass up to working

options, operating temperatures and prices.The lampworker will advise the

COSTS

designer as to which is most suitable for

There are usually no tooling costs, while

and oxygen are burnt to produce heat.

their particular application.

cycle time Is moderate, but depends

The combustion is non-toxic, but the

on the size and complexity of the part.

glass becomes so bright when it is heated

temperature. A mixture of natural gas

COMPATIBLE MATERIALS

The annealing process Is usually run

that protective eyewear must be worn.

All types of glass can be formed by

overnight, for up to 16 hours, but can

The glasses are fitted with didymium

lampworking.The 2 main types are

take a lot longer depending on material

lenses, which filter the bright yellow

borosilicate and soda-lime glass.

thickness.Very thick glass may take

sodium flare and prevent cataracts.They

Borosilicate glass is a'hard glass'known

several months to anneal, because in

also enable the lampworker to see what

underthe leading trade names Pyrex®,

such cases the temperature is lowered by

he or she is doing.

Duran® and Simax®. It is very resistant

only i.50C (2.70F) per day.

to chemicals, so is ideal for laboratory

brought together and heated until the glass

over the mandrel; if it is too hot, the glass will

A U-bend is then worked in another tube

The glass must have equal coefficient of

The stillhead parts are then almost

Labour costs are high due to the

equipment, pharmaceutical packaging

level of skill required-lampworking

and preservation jars. Soda-lime glass, on

being complex and therefore not

Featured Manufacturer

Dixon Glass www.dixonglass.co.uk

— ,

¦

Case Study

Latheworking the triple walled reaction vessel A lathe can be used to form large and smal)

a hole is opened out using another profiled

parts very accurately. The only requirement

carbon bar (image 3). These form the first 2

Once all 3 jackets of the reaction vessel are brought together, an extension tube is fused

is that they are rotationally symmetrical up

reaction vessel jackets, which are assembled

onto the bottom, using the heat of the gas

to a certain point (the final part may have

off the lathe (image 4). Throughout the

torch in much the same way as benchworking

additions that are not symmetrical).

process the assembly has been spinning to

(image 8). Some extra touches are added by

The operation starts with a large tube section being heated gently to raise its

ensure even heat distribution.

A rod of glass is used to pick hot glass from

temperature while spinning at approximately

the melt zone (image 5) and to bore a hole

5o rpm (image i).The neck of the innermost

(image 6). The hole Is opened out and the 2

jacket is formed with intense localized heat

parts are fused together using the profiled

and a profiled carbon bar (image 2). The 2

carbon bar (image 7). The process is repeated

halves of the tube section are separated, and

for the third and final jacket.

boring and joining onto the outer jacket of the reaction vessel (images 9 and 10) to create the semi-finished product (image n).

> CO CO

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Featured Manufacturer Dixon Glass www.dixonglass.co.uk

TECHNICAL DESCRIPTION

Throwing Process

In stage 1 for wheel thrown pottery,

the clay body is 'pugged' in a pug mill.

Electric motor

This process has 2 main functions: it

thoroughly mixes and conditions the

Forming Technology

Air pocket

Clay Throwing

clay for throwing, and it removes some

_ Mixing paddle

of the air pockets. Some pug mills

Drive shaft

are equipped with a vacuum pump to remove even more air. Pugging is

Ceramic products that are symmetrical around an axis of rotation

INTRODUCTION

can be made on a potter's wheel. The style, shape and function of

Throwing (also known as turning) is used to produce sheet and hollow shapes that

each piece can be as varied as the potter who creates it, and each

frequently carried out at the beginning of the day, for 1 hour or so, in order to

produce sufficient pugged clay for a day's throwing. Prior to throwing the

are rotationally symmetrical. It is often

clay is 'wedged' by hand to improve the Rotating clay pot

combined with other processes to make

studio adapts and develops their own techniques.

working consistency of the material.

more complex products, with handles

In stage 2, the predetermined

and feet, for example.

quantity of clay is 'thrown' onto a 'bat',

Clay throwing has been used for Costs

Typical Applications

Suitability

centuries all over the world to create a

1 No tooling costs 1 Low to moderate unit costs

• Gardenware • Kitchenware • Tableware

• One-off and low volume production

diversity of products. The process relies

Quality • Variable, because handmade

Related Processes • Ceramic slip casting • Press molding ceramics

which is then placed on the potter's Extruded clay plug

wheel. The ball of clay is centred on the spinning wheel, which is generally

Potter's wheel

on the skill of the potter to create high

powered by an electric motor but can

quality and uniform pieces.

be driven by a kick wheel.

TYPICAL APPLICATIONS

gradually draws the clay vertically

While the wheel turns, the potter

Speed • Moderate cycle time (15-45 minutes), depending on size and complexity • Long firing process (8-12 hours)

upwards, to create a cylinder with an

Generally clay throwing is used to

Stage 1: Pug mill

Stage 2: Throwing

produce one-off and short production

even wall thickness. Clay throwing must always start In this way, to ensure

runs of gardenware such as pots and

parts will be rotationally symmetrical.

but depends on the complexity and size

fountains. Kitchenware and tableware,

To create asymmetric shapes, other skills

of the part. For example, simple shapes

such as pots, jugs, vases, plates and bowls,

such as handwork, carving and pressing

can be produced within 15 minutes or so,

are also manufactured in this way.

are combined with clay throwing. Knobs,

whereas tall or particularly 1 arge parts

feet, spouts and other embellishments

may have to be formed in stages, which

can be added post-throwing.

air dried together for about an hour,

weather and ambient temperature

RELATED PROCESSES

even wall thickness and distribution of stress, even though the shape can

subsequently be manipulated into a variety of geometries.

The bat and thrown part are then

press molded ceramics (page 176)

DESIGN CONSIDERATIONS

prolongs cycle time.The firing time can be quite long and is determined by whether the parts are biscuit fired and

use molds and so are more suitable

The size of part is restricted by the skill of

then glaze fired, or are once-fired only.

for making identical parts than clay

th.e potter, the quality of the wheel, the wall thickness and the size of the kiln.

each potter requires a high level of

At this point the part is trimmed, to

Wall thickness ranges from 5 mm (0.2 in.)

technical ability to throw accurate pieces.

remove any excess material, and

Slip casting ceramics (page 168) and

throwing.

QUALITY

Labour costs are moderate because

ENVIRONMENTAL IMPACTS COMPATIBLE MATERIALS

pots tend to have a variable quality that depends on the skill of the potter and on

Clay materials including earthenware,

this pottery-forming process. Any scrap

the material itself. Earthenware is the

stoneware and porcelain can be thrown

produced during the throwing process

most commonly used pottery ceramic.

on a potter's wheel. Porcelain is the

can be directly recycled. Once fired,

It is brittle and porous and has to be

most difficult material to throw and

discarded pieces are not reworked into

sealed with a glaze to be watertight.

earthenware the easiest, because it is

thrown clay unless special effects are

Earthenware garden products are prone

more robust and forgiving (see ceramic

required. Some studios,for example, mix

to crack in freezing conditions because

slip casting).

'green'and fired clay with fresh clay to

they absorb water.

There are no harmful by-products from

affect how long clay takes to dry out.

as feet, handles or stands.

The firing process can be carried out in the same way as with ceramic

slip casting and press molding ceramics, or it can be done in a single operation, known as 'once-fired'. Parts

produce speckled and decorative effects.

COSTS

or until the clay is leather-hard. The

assembled with any other parts such

for small parts up to 25 mm (1 in.).

Because they are handmade, thrown

removed from the potter's wheel, and

The firing process is energy intensive.

DESIGN OPPORTUNITIES

There are no tooling costs for the clay

Therefore the kiln is fully loaded for each

By the very nature of this process all

throwing process. Cycle time is moderate.

firing cycle.'Once-firing'reduces energy

with delicate features, such as cups

with handles, are biscuit fired first to minimize the risk of breaking during glaze firing.

Case Study

Hand throwing a garden pot Although premixed day is supplied to the

in i throw, as here, a second level of day

first until it is the same diameter and wall

studio (image i), it still has to be pugged in a

needs to be added. Potters have developed

thickness at the top (image 10). It does not,

pug mill and 'wedged'by hand.The extruded

a technique that enables them to build a

however, have a solid base. It is turned upside

pug of day is weighed into predetermined

pot higher than 1 throw would usually allow,

down and placed carefully on top of the first

quantities and worked by hand into the

but it takes a great deal of skill because the

part (image 11). The clay parts are aligned

correct consistency for throwing (image 2).

lower part has to match the additional piece

and joined together. Once the bat has been

Pummelling the clay levels the density of the

very accurately.

removed from the base of the top part, the

material and makes it supple for shaping. The predetermined quantity of day is then

The sides of the first part are smoothed (image 5) and then the top is finished with

thrower smooths the joint line and continues to shape the pot upwards (image 12).

thrown down onto the bat. This action makes

a level top, achieved using a flat blade. Its

the clay denser at the base, which helps to

height and diameter are checked (image 6)

give it strength.The lump of clay is rotated

and it is fired with a gas torch, which hardens

is to be once-fired, the glaze is applied before

and 'centred' by hand, until the mass of the

the clay very slightly and just enough for it to

the pot has been biscuit fired. The wet glaze

clay is rotationally symmetrical and can be

be self-supporting (image 7). Once the clay is

is painted on using a small pipette (image

shaped. The potter then makes a doughnut

sufficiently green-hard, the top is trimmed for

13). The pot is placed in the kiln for firing at

shape (image 3), which is drawn up into a

a second time (image 8).

lyoo'C (3092°?) for 8-12 hours (image 14),

cylinder with even wall thickness (image 4). Once the cylinder has reached the desired

For the second part of the pot, the potter's

wheel is prepared (image 9) and another ball

height the part can be shaped. However, if the

of clay is thrown onto the bat. The second

day pot being made is too high to be shaped

part is thrown in much the same way as the

Featured Manufacturer S. & B. Evans & Sons www.sandbevansandsons.com

The completed pot is left to air dry until it is green-hard throughout. Because this pot

after which the finished pot is removed from the kiln (image 15).

Slip Casting Process

Preprepared

Flash lines to be removed i Molds : separated

Forming Technology

Ceramic Slip Casting

1 Part ready for trimming, assembly and firing

Identical hollow shapes with an even wall thickness can be

molded in several pieces and assembled, or be formed in a multiple-part mold.

produced with this versatile ceramic production technique. It is

Assembly operations are preferably

used in the manufacture of many familiar household items and

avoided because of their cost, but they are sometime unavoidable. It is very

remains a largely manual operated process.

important that the product is designed

Stage 1: Fill with slip Stage 2: Ceramic deposit forms

Stage 3: Demolding

with consideration forthe process.

TECHNICAL DESCRIPTION 1 Low tooling costs Moderate to high unit costs

Quality

I

• Surface finish determined by mold, glaze and skill of the operator

Typical Applications

Suitability

DESIGN CONSIDERATIONS

In stage 1, the mold is prepared so It Is

• Bathroom whiteware • Kitchen and tableware • Lighting

• Low volume and batch production

The slip casting process relies on a

clean and free from any previous slip

carefully removed from the mold and

porous plaster mold drawing moisture

contamination. For intricate molds and

fettled to remove any flash.

small details a fine dust can be used to

Related Processes

Speed

• Clay throwing • Press molded ceramics

• Moderate cycle time (0.4-4 hours), depending on size and complexity • Long firing process (up to 48 hours)

from the slip by capillary action.The slip must be exactly the right consistency and the plaster mold sufficiently dry so that they work in harmony.

taken to ensure that the molds are

can withstand manhandling. The length

The design and construction of the

plaster mold will have an impact on the

INTRODUCTION

cream ware (a type of earthenware made

QUALITY

quality of the slip casting. Plaster molds

Ceramic slip casting is ideal for the manufacture of multiple identical

from white Cornish clay combined with

The overall quality of the final piece is

are generally produced directly from

a translucent glaze), and stoneware and

largely dependent on the skill of the

the master, which can be made of clay,

products. A permanent plaster mold can

operator.The materials used in slip

wood, rubber or other modelmaking

casting are generally quite brittle and

material.The parting lines are worked

replacing, and automated slip casting

porcelain (fine, high quality materials that can be fired at high temperatures to enhance their shiny white and

porous, which means that they are not

techniques can make many thousands of

sometimes translucent qualities).

very tough and tend to fracture rather

produce up to 50 pieces before it needs

parts. Numerous household objects and

than deform underload. Earthenware,

In stage 3, the 'leatherware' is

The next stages of processing depend

ensure that the slip casting and molds

on the surface treatment that is going

release cleanly. The molds are fastened

to be used. The parts are left to air dry

together with rubber bands - care being

so that they are self-supporting and

secure and can withstand the appropriate

of time Is determined by the weather

internal pressure, because slip is a

conditions, because hot weather will

relatively heavy material, about twice the

cause the clay to dry out more quickly.

weight of water.

Following cutting, assembly and

Meanwhile, the casting slip has been

sponging, the parts are further air dried

prepared by mixing together clay, silicate,

until the ceramic turns whitish in colour,

soda ash and water. The consistency of

known as 'greenware'. The parts are now

out to optimize production and reduce

the slip is essential for the success of the

ready to be biscuit fired, to remove all

assembly operations.

casting: It must be well blunged and free

remaining moisture. This takes place in

Shrinkage is in the region of 8%, but

from lumps. The mold is filled with the

a kiln over 8 hours. The temperature of

depends on the type of material. Draft

slip and left to stand for 5 to 25 minutes.

the parts is raised to 1125°C (2057oF) and

porous and so have to be glazed to be

angles are not usually a problem because

The length of time the slip is in the mold

retained at that level for 1 hour before

watertight. Stoneware and porcelain,

the molds are inward curving.

and the ambient temperature determines

cooling slowly.

tableware items are produced using this

TYPICAL APPLICATIONS

casting technique.

Slip casting is used to form a wide variety of household items such as basins,

is a finely ground (particle size around

lighting, vases, teapots, jugs, dishes,

on the other hand, have much better

1 micron/0.000039 in.) mixture of clay,

bowls, figurines and other utilitarian

mechanical properties, even though they

is limited for practical reasons such as

minerals, dispersing agents and water.

and decorative objects forthe bathroom,

are still quite brittle.

weight and fragility of the material.

moisture from the slip, causing the

Traditionally, the type of ceramic slip

kitchen and table.

However, large parts, such as shower

clay platelets to pile up around the

'biscuitware' is then glaze fired using

trays, are feasible for ceramic slip casting.

mold wall and create a ceramic deposit

the same cycle as biscuit firing. When

(shell). When the ideal wall thickness Is

the finished ceramic slip castings are

The ceramic slip (also known as slurry)

terracotta and creamware are the most

DESIGN OPPORTUNITIES

used was determined by the location of

the factory because the local clay would

RELATED PROCESSES

This process can be used to produce a

be incorporated in its production.

Clay throwing (page 168) is suitable for

range of both simple and complex 3D

Pottery is the general term used to describe ceramic materials that

The size of part that can be slip cast

COMPATIBLE MATERIALS

sheet geometries. However, it is generally

sheet and hollow geometries. Simple

Ceramic materials such as earthenware,

associated with one-off and low volume

shapes can be slip cast in a single

terracotta, creamware, stoneware and

are suitable for slip casting. Well-

production of idiosyncratic products.

operation, without any assembly: for

porcelain can all be slip cast.The main

known types of pottery materials

Press molding ceramics (page 176) is

example, a conical or straight-sided jug

ingredient for all of the compatible

include earthenware and terracotta

productive and repeatable like ceramic

with handle and spout can be molded in 1

pottery materials is clay, which is

(characteristically reddish orange but its

slip casting, but its application is also

piece. By contrast, objects with undercuts

a natural material that can be dug

colouring varies from country to country),

limited to sheet geometries.

or other intricate details may need to be

up from the ground. It can be mixed

the wall thickness. In stage 2, the plaster mold draws

Following the first firing all remaining surface decoration, such as glazing and hand painting, is carried out. The

achieved the slip Is drained (or poured)

removed from the kiln they are watertight

from the mold. The mold is left to stand

and rigid.

for anything between 1 and 1U hours to ensure that the ceramic shell is sufficiently leather-hard to be removed from the mold.

Case Study

Slip casting the puzzle jug A total of three molds are used in the

mold (image 3).The slip casting is left in the

production of the puzzle Jug. Each mold is

mold for 45 minutes while the plaster molds

even though they have been handmade.

cleaned and prepared and the bottom of the

continue to draw moisture from the slip and

A slip is used to join the parts together so

mold so that each jug will look very similar

mold and the locating points to the main

turn it leather-hard (image 4).The slip casting

they will become integral to the structure

body of the mold are checked (image 1). In

can then be demolded, but this has to be

during biscuit firing. The assembly process

turn each mold is filled to the brim with

carried out very carefully to make sure that

consists of inserting and fixing the inner skin

casting slip made from earthenware (image

it retains its shape (image 5). The casting is

(watertight) and outer skin together at the

2). The molds are left to stand for 15 minutes,

then left to air dry before any further work is

rim, using slip (images 8 and 9), and placing

or until a sufficient wall thickness has built

carried out (image 6).

the handle on the jug (image 10).

up as a deposit on the inside mold wall. The

The outer skin of the puzzle jug is then

remaining slip is poured from the mold into

pierced using a profiled punch (image 7).The

a bath, where it will be recycled for another

floral pattern is marked very lightly on the

After biscuit firing a cream glaze is applied (image 11). The glaze is blue so that the operator can see where the glaze has already

been applied. Finally the puzzle jug is placed into the kiln for glaze firing, which takes up

>

to 8 hours (image 12), after which the finished

o w

jug is removed from the kiln (image 13),

o > cn

with water and a number of different

Ideally, plaster molds comprise only 2 or 3

minerals to create various ceramic slips.

pieces in order to maintain cycle times.

Deflocculants are added to the slip to

Labour costs are moderate to high due

decrease the amount of water required

to the level of skill required, and they can

to make it fluid. This is achieved by aiding

be especially high in handmade pieces.

the suspension of the clay particles in

This is by far the 1 argest expen se an d it

water and reducing the porosity in the

determines the cost of the parts.

final product.

ENVIRONMENTAL IMPACTS COSTS

During slip casting there can be up to

Tooling costs arelow.The plaster molds

15% waste.The majority of this waste can

are generally produced from a rubber or

be directly recycled as slip. However, if the

clay master, which takes a great deal of

parts have been fired then the ceramic

skill to create.They must be engineered

is no longer suitable for recycling.There

not only to eliminate undercuts, but also

are no harmful by-products from these

to contain the least number of pieces.

pottery-forming processes.

Featured Manufacturer Hartley Greens & Co. (Leeds Pottery) www.hartleygreens.com

TECHNICAL DESCRIPTION

Jiggering Process

A plaster 'male' mold is used in the jiggering process and a 'female' one

for the jolleying process. In stage 1, the mold is mounted onto a metal carrier

Forming Technology

attached to an electric motor that spins

Press Molding Ceramics

at high speed. A charge of mixed clay is loaded onto the clean mold. In stage 2,

as the mold and clay spin, the jiggering

Ram pressing, jiggering and jolleying are all techniques for

arm is brought down onto the clay. A

manufacturing multiple replica ceramic parts with permanent

which is different for each mold shape,

profiled former with a shaping blade, forces the clay to take the shape of the

Stage 1: Open mold, loading and unloading

molds. They are used in the production of kitchen and tableware,

rotationally symmetrical mold. The

Finished part trimmed and removed on the mold for support

profiled former determines 1 side of

including pots, cups, bowls, dishes and plates.

the clay part and the mold determines the other side. The process is very rapid and takes less than a minute.

Costs

Typical Applications

Suitability

• Low to medium tooling costs • Low to medium unit costs, depending on level of manual input

• Kitchen and tableware • Sinks and basins • Tiles

• Low to high volume production

Once the final shape is complete and the edges have been trimmed, the Pressure applied to shape the clay over the plaster mold

Quality

Related Processes

Speed

• High quality finish

» Ceramic slip casting » Clay throwing

• Rapid cycle time (1-6 per minute], depending on level of automation • Long firing process (up to 48 hours)

Plaster mold rotates at high speed — Metal carrier

mold and clay are removed from the metal carrier intact. The clay part is

left on the mold until it is sufficiently 'green' to be removed. If the part is

demolded immediately It will deform Stage 2: Closed mold

because the clay is still very supple.

The length of time is determined by

INTRODUCTION

and tableware vessels), sinks and basins,

DESIGN OPPORTUNITIES

In this process, clay is forced into sheet

jewelry andtiles.

COSTS

Jiggering and ram pressing can be used

andprofiling tool to shape the clay.This means that jiggering is more suitable for

Tooling costs for jiggering are relatively

the weather conditions and ambient temperature: a hot environment will cause the clay to dry out more

to produce most shapes that can be

prototyping and shot production runs.

low because a single sided mold is used.

Parts are compressed and have an even

RELATED PROCESSES

slip cast in a 2 part mold. Using molds

For volume production multiple tools are

wall thickness. Press molding is often

Clay throwing (pagei68) and ceramic

increases repeatability and uniformity

The heat of the ram press molds 1 e ath er h arden s th e cl ay duri n g th e

required because the clay has to be left

piercing or assembly, then the clay

em ployed for the mass production of

slip casting (page 172) are used to make

of part, so even tall objects are easily

pressing cycle, which means that the

on the mold to air dry.

part Is transferred onto a 'female'

popular ceramic flatware andtiles.

similar products and geometries.

produced with minimum skill. Manual

part can be removed from the mold

Press molding differs from them by

operations, such as adding handles and

immediately. Jiggered parts, on the

are in the region of 10-20 times the cost

press ceramics are jiggering (known as

specializing in high volume and the rapid

spouts, ten d to require a hi gher 1 evel of

othex hand, have to be left to air dry on

of jiggering molds. However, they have a

jolleying if the mold is in contact with the outside surface of the part rather than

production of identical parts.

operator skill.

the mold. This causes a problem, in that

higheryield than jiggering molds, more

many molds have to be used to form

rapid turnover and they last many more

waste caused by inconsistency.There

the inside surface) and ram pressing.

OUALITY

being able to produce shapes that are

multiple products and these take up a

cycles (approximately 10,000).

are no harmful by-products from these

Although both of these processes can be

The pottery materials used in press

not rotationally symmetrical. Many

large amount of storage space.

automated, jiggering andjolleying are

molding are brittle and porous (see

design features (handles and decoration,

often carried out as manual operations

ceramic slip casting), so the surface is

for example) can be pressed directly onto

and can be used only on geometries

often made vitreous by glazing, which

the part to reduce or eliminate assembly

that are symmetrical around an axis of

provides a watertight seal.

and cutting operations.The part is

COMPATIBLE MATERIALS

pressed and cut in a single operation,

Clay materials including earthenware,

operations, but for automated

thereby reducing cycle time dramatically.

stoneware and porcelain can be pressed.

techniques they are relatively low.

geometries using permanent molds,

The 2 main techniques used to

Ram pressing has the advantage of

Shrinkage is in the region of 8%, but does depend on the type of material.

Ram pressing uses split molds, which

Cycle time is rapid for ram pressing

and slightly slowerfor jiggering.

quickly, if there are secondary operations to be carried out, such as

support mold.

pottery forming processes. The firing process is energy intensive,

Automated processes accelerate

so therefore the kiln is fully loaded for

production of press moldings.

each firing cycle.

Labour costs are higher for manual

rotation. Ram pressing can be utilized to

A very high surface finish can be

make symmetrical shapes as well as oval,

achieved with both jiggering and ram

square, triangular and irregular ones.

pressing techniques. When compared to ceramic slip casting and clay throwing,

DESIGN CONSIDERATIONS

not watered down for these processes.

ENVIRONMENTAL IMPACTS

TYPICAL APPLICATIONS

press molding has the advantage of

The 2 part mold used in ram pressing has

However, it is essential that the material

In all pressing operations scrap is

Uses for press molding ceramics include

producing parts that are uniform and

to be made to tight tolerances to ensure

i s suffi ci ently m oi st to fl ow duri n g th e

produced at the 'green' stage and so

flatware (such as plates, bowls, cups

compressed and therefore less prone

accurate and uniform reproductions. By

pressing cycle. The clay used for ram

can be directly recycled. Using molds to

and saucers, dishes and other kitchen

to warpage.

contrast, jiggering uses a single mold

pressing is slightly stiffen

reproduce the parts accurately reduces

Unlike ceramic slip casting, the day is

Case Study

Jiggering a plate If numerous identical parts are being made

profiled former shapes the outside surface

the plate is transferred onto a female support

biscuitware is then placed in specifically

with this process, then multiple plaster molds

while the mold shapes the inside surface

mold. The rim can then be pierced without

designed 'setters' and glaze fired using

are required (image i) because the parts have

(image 4). While the part is still spinning

forcing it out of shape (image 7). The part is

the same cycle (image 9). When the

to be left on the molds while they harden to a

on the mold, the edge is trimmed, to form a

then ready to be biscuit fired, to remove all

finished ceramic plates are removed from

'green' state. Each mold is made individually.

perfectly symmetrical shape (image 5). The

remaining moisture. This takes place in a kiln

the kiln they are watertight and rigid

mold and clay part are removed intact, so that

over 8 hours. The temperature of the parts is

(image io).

the clay can air dry and harden sufficiently

raised and then soaked at i^s'C (2057°F)fon

out to form an even and uniform 'pancake' of

before it is removed from the mold for biscuit

hour before cooling slowly.

clay (image 2). The pancake is then transferred

firing (image 6).

To press mold each part, a charge of mixed

clay is spun on a jiggering wheel so it spreads

onto the plaster mold (image 3). The jiggering arm is brought down onto the day and a

In this case the piece of flatware is to be pierced and so after a few hours of air drying

Following the first firing, all remaining surface decoration is carried out such as

glazing (image 8) and hand painting. The

I

Featured Manufacturer Hartley Greens & Co. (Leeds Potteryl www.hartleygreens.conn

TECHNICAL DESCRIPTION

Ram Press Process

This is an automated process that forms parts by hydraulic action. Each product

will be identical and manufactured to fixed tolerances. The molds are typically made of plaster, although these have

Metal die casting

a limited lifespan. The die casings can be made to accommodate either 1 large

Cutting edge

part or several smaller objects. In stage 1, a charge of mixed clay is

Charge of clay Hydraulic ram

Metal die casting

loaded into the lower mold. In stage 2,

Porous lower mold

the upper and lower molds are brought together at pressures from 69 N/cm2 to

276 N/cm21100-A00 psi). The pressure

Stage 1: Open mold, loading and unloading Finished part removed and trimmed

is evenly distributed across molds and through the clay, which produces even

Upper platen

and uniform parts. During the pressing cycle the warm plaster molds draw moisture from the clay, to accelerate

Excess flash

the hardening process. The perimeters

Pressed flatware

of each mold cavity on the upper and Lower platen

lower section come together to cut the excess flash from the clay part. The

Stage 2; Closed mold

ram pressing process is more rapid that

jiggering and can produce up to 6 cycles every minute.

Once the pressing cycle is complete, the molds separate and the parts are instantly released by steam pressure that is forced through the porous molds. The clay parts are self-supporting and

can be demolded immediately after they have been ram pressed.

Case Study

Ram pressing 2 dishes The day used in ram pressing needs to be slightly stiffer than for jiggering. Some

The molds are separated and any excess

flash is quickly removed for reprocessing

measured charges of mixed clay are cut from

(image 5). The clay parts are instantly ejected

the pug roll (image i).The charges of clay

by steam pressure, which is forced through

are placed into the lower mold cavity (image

the porous plaster mold (irnage 6). The

z) and the 2 halves of the mold are brought

parts are self-supporting as soon as they are

together (image 3). The pressure forces the

demolded because the ram pressing process

clay to flow plastically through the mold

dehydrates the clay during the pressing cycle,

cavity and to squeeze out as flash around the

and this hardens it sufficiently for immediate

edge (image 4).The flash is cut as the molds

biscuit firing. Ram pressed clay parts take

come together and the edges of the mold

glaze and other decoration very well, as the

cavities make contact.

surface is compressed and uniform.

Featured Manufacturer Hartley Greens & Co. (Leeds Pottery) www.hartleygreens.com

TECHNICAL DESCRIPTION

CNC Machining Process

Among the many different types of

Track for Dust extraction unit

CNC machinery, CNC milling machines

O

Forming Technology

yand zaxes

CNC Machining

and CNC routers are essentially the same, CNC lathes, on the other

hand, operate differently because the workpiece is spun rather than the tool.

The woodworking and metalworking Track forx- and y-axis movement

Using CNC machining, CAD data can be transferred directly onto the workpiece. The CNC process is carried out on a milling

Guard

INTRODUCTION CNC machining encompasses a range

traced back to when these materials Chuck and spindle

milling, routing, lathe turning, drilling Vacuum clamp

(boring), bevelling, reaming, engraving

quality end product.

1 • Low tooling costs 1 • Low unit costs

Suitability

materials. The terminology and use

• Automotive • Furniture • Tool making

• One-off to mass production

of CNC machining is related to the

a z-axis track (vertical). Some older versions, or reconditioned machines, Track for z-axis movement

traditional material values of each

Track forx- and y-axis movement

particular industry. For example, CNC

1

Quality

Related Processes

Speed

• High quality finish that can be improved with grinding, sanding and polishing

• Electrical discharge machining • Electroforming • Laser cutting

• Rapid, but depends on size and number of operations

specific tools and equipment.

x- and y-axis tracks (horizontal) and

3-axis CNC with tool carousel

industries for shaping metal, plastic, Typical Applications

were hand worked using material-

Most modern CNC machinery has

and cutting out. It is used in many wood, stone, composite and other

Costs

names for similar tools and operations - the names and practices can be

of processes and operations including

machine, lather or router, and results in a rapid, precise and high

industries will probably use different

have an x- and y-axis table Instead.

Beyond this, there are CNC robotics in development that will occupy a space and move freely within it, rather than

woodworking is affected by grain,

being fixed to a table with tracks. The

greenness and warpage. By contrast,

new technology relies on data for each

CNC metalworking is concerned with

part to be preprogrammed, so that it

Pivoting head

can locate machining and assembly

Pivoting router

operations for each individual piece as it comes across them.

Chuck

Many different tools are used in the cutting process, including cutters (side

Cutting tool

or face), slot drills (cutting action along the shaft as well as the tip for slotting

Table

and profiling), conical, profile, dovetail and flute drills, and ball nose cutters 5-axis CNC with interchangeable tools

(with a dome head, which is ideal for 3D curved surfaces and hollowing out). By contrast, CNC lathes use single-

1 ubri cation, m inute tol eran ces an d th e

rotation are vertical and horizontal, to

point cutters because the workpiece

heat-affected zone (HAZ).

achieve 360° of possible movement.

is spinning.

The number of axes that the CNC

The principles of CNC manufacturing

machine operates on determines the

can be applied to many other processes

geometries that can be cut. In other

such as ultrasonics, fusion welding and

words, a 5-axis machine has a wider

plastic molding.

examples. The 3-axls CNC machine has a tool carousel with an array of cutting tools and drills. This accelerates

range of motion than 2-axis one.The

\ - * a*

There are several ways to change

the cutting tool and here are two

the cutting process dramatically

type of operation can also determine the

TYPICAL APPLICATIONS

number of axes. For example, a lathe has

Almost every factory is now equipped

only 2 possible axes of motion (the depth

with some form of CNC machinery. It is

of cut and position along the length of

an essential part of both prototyping

be changed by hand, but this Is rare.

the workplace), whereas a router can

and mass production lines.Therefore,

In most cases there Is a separate

operate on all 5 axes of possible motion

applications are diverse and widespread

magazine that Is loaded with a set of

(x,y and z axes, and 2 axes of rotation).

across the manufacturing industry.

tools that the CNC head will locate and

The x andy axes are typically horizontal an d th e z axi s i s vertical. Th e 2 axes of

CNC machining isusedfor primary operations such as the production

and tool changes are instant. The 5-axis machine has a single tool. On both CNC machines, the tools can

use automatically.

Case Study

CNC carving the Ercol Windsor chair CNC machining can be used to cut and

With a slot drill, the 3-axis CNC machine

shape a wide range of materials. In this

cuts the external profile of the seat (image

case study, it is used to make the various

3), after which the tool carousel is rotated

components that comprise the beech Erco)

and the edge is profiled with a separate

Windsor chair, Ercol is a manufacturer of

cutting tool (image 4),Then, material is

traditional and contemporary wooden

removed from the top side of the seat

furniture, and they mix craftsmanship

by a dish-shaped cutter, to produce the

with new technology. This combination is

ergonomic profile required (image 5). The

very interesting as it illustrates the vast

process takes less then 2 minutes before

possibilities of CNC machining working

the seat is removed from the vacuum

alongside other processes,

4

3

clamp. A seal runs around the periphery of the vacuum clamp and it maintains the

CNC ROUTING THE SEAT

vacuum within the grooves incised across

A plank of wood is prone to warping and

its surface (image 6). This is a very quick and

buckling. For this reason, the planks used

effective method for clamping continuous

in the seat of the chair are first cut into

runs of the same parts. Because the seat

small widths, which are flipped and glued

is not quite finished it is stacked up for

back together with butt joints (image i).

secondary operations (image 7).

Each section of wood in the plank will then balance the forces of its neighbours. The

Holes are required for assembly, but the 3-axis CNC machine is capable only

planks are cut to size and loaded onto the

of profiling vertical holes. The seats are

CNC machine table (image 2). The parts

therefore loaded onto a 5-axis CNC, which

are pushed firmly onto the vacuum clamp,

drills holes at the correct angle for the legs

which is activated to hold the piece in place.

and back to be assembled.

QUALITY

In operation, there is no difference

This process produces high quality parts

between simple and complex shapes,

with close tolerances. CNC machining

and straight or curved lines.The CNC

is accurate across 2D and 3D curves and

machine sees them as a series of points

straight lines. Depending on the speed of

that need to be connected.This provides

operation, a CNC machine leaves behind

limitless design opportunity.

telltale marks of the cutting process. These can be reduced or eliminated of prototypes to minute tolerances, toolmaking and carving wood. More often, however, it is utilized for secondary operations and post-forming, Including the removal of excess material and boring holes.

RELATED PROCESSES CNC machining is versatile and widely used, competing with many other processes. For toolmaking, it is the most

cost effective method of production up to approximately 1 m3 (35 ft3). Any larger and electroforming (page 140) nickel becomes more cost effective.

Laser cutting (page 248) is suitable for profiling and shaping metals apd plastics as well as other materials. It is rapid and precise and more suitable for certain

applications, such as profiling sheet poly methyl methacrylate acrylic (PMMA). Electrical discharge machining (EDM) (page 254) is used to profile and shape metals. It is used for concave shapes that are not practical for machining.

CNC machining is also used to prototype and manufacture low volumes

of parts that can be formed by steam bending (page 198), die casting (page 124), investment casting (page 130), sand casting (page 120) and injection molding.

DESIGN CONSIDERATIONS

by, for example, sanding, grinding or

Most CNC machining is almost

polishing (page 376) the part.

completely automated, with very little operator interference.This means that

DESIGN OPPORTUNITIES

the process can run indefinitely once

CNC machining can be used to produce

started, especially if the CNC machine

3Dforms directlyfrom CAD data.This

is capable of changing tools itself. The challenge for the designers is to utilize the equipment available; it is no good

is very useful in the design process,

especially for prototyping and smoothing the transition between design and production of apart.

Some CNC machining facilities

designing a part that cannot be made in the identified factory. For parts with geometries that need

are large enough to accommodate a

different cutting heads or operations,

full-scale car (and larger, up to 5 x 10 x

multiple machines are used in sequence.

5 m/16.5 x 33 x 16.5 ft) for prototyping

Once up and running, the CNC process

purposes. Many different materials can

will repeat a sequence of operations very

be machined in this way, including foams

accurately and rapidly. Changing the set¬

and other modelmaking materials.

up is the major cost for these processes,

1,

CNC LATHE TURNING THE CHAIR LEGS The legs and spokes for the chair back are rotationa)ly symmetrical and produced on a CNC lathe. Cut and profiled timber is loaded into the automatic feeder (image 8). This in turn is loaded onto the lathe centres (image 9), which are 'alive'

and rotate with the workpiece (they are known as dead centres when they are

stationary). Each workpiece is spun between the headstock andtailstock of the lathe at high speed (image 10). Parts with large cross-section are spun more

slowly because the outside edge will be spinning proportionately faster. The cutting action is a single, smooth arc made by the cutting head, which carves the workpiece as a continuous

shaving (image 11). These images depict the profiling of a chair leg, which requires a second cutting operation to form a 'bolster' (shoulder) in the top for locating the leg within the seat (image 12). Vertical holes are drilled for the cross bars, which make up the leg assembly (image 13). The profiled legs are loaded into crates for assembly in batches (image 14). They still have a'handle' attached to the top end, which is waste material removed prior to assembly.

and subcontractors often charge set-up

Cycle time is rapid once the machines

time separately from unit costs. As a rule,

are set up. There is very little operator

larger parts, complex and Intricate

involvement, so labour costs are minimal.

shapes and harder materials aremore expensive to machine.

ENVIRONMENTAL IMPACTS This is a reductive process, so generates

COMPATIBLE MATERIALS

waste in operation. Modern CNC systems

Almost any material can be CNC

have very sophisticated dust extraction,

machined, including plastic, metal, wood,

which collects all the waste for recycling

glass, ceramic and composites.

or incinerating for heat and energy use.

The energy is directed to specific parts

COSTS

of the workpiece by means of the cutting

Tooling costs are minimal and are limited

tool, so very little is wasted. Dust that is

to jigs and other clamping equipment.

generated can be hazardous, especially

Some parts will be suitable for clamping

because certain material dusts become

in a vice, so there will be no tooling costs.

volatile when combined.

ASSEMBLING THE ERCOL WINDSOR CHAIR Each chair is assembled by hand because wood is a'live'material which will move and crack and so parts need to be

individually inspected. Adhesive is used in all the joints and soaks into the wood grain to create an integral bond between the parts.

Adhesive is added to each joint with a cue tip (image 15).The legs and cross bars are then carefully put together and the joints 'hammered home' (image 16).The legs come right through the seat and a wedge is driven into the legs' end grain to reinforce the joint (image 17). Once the adhesive is dry the excess material is removed from the seat with a belt sander and a shaped sanding block (image 18). Sanding also improves the cut finish left by the CNC machining. Meanwhile, the backrest for each chair will have been steam bent, the vertical spokes profiled to shape on a CNC lathe, and the relevant parts glued together. After the legs and seat have been assembled the backrest is put in place (image 19), the joints being glued and reinforced in the same way as the legs.

Once the legs have been cut to the same length, the assembled chair is ready for surface finishing (image 20). Featured Manufacturer Ercol Furniture 17

www.ercol.com

Wood Laminating Processes Adhesive applied to inside surfaces

In this process, a series of parallel cuts

Kerfing 1 Parallel

are made in one side of the workpiece.

UIMIMUT IMJUlfUMr

Forming Technology

TECHNICAL DESCRIPTION KERFING

This can be done with a band saw, table saw or router. The kerfs are usually

Grain runs perpendicular to cuts

Wood Laminating

Parts bent by hand or over a mold

between one-third and three-quarters

of the depth of the workpiece. Locally reducing the thickness of material

Multiple sheets of veneer or solid timber are formed using molds and bonded together by very strong adhesives, to produce rigid, lightweight structures.

makes It more pliable, and a smooth

INTRODUCTION There is nothing new about the process

bend can be achieved if the kerfs are

Solid wood lamination

cut close together. In the diagram 2

of bonding 2 or more layers of material

matching kerfed boards have been

together to form a laminate. However,

bent and bonded together to hide the

as a result of developing stronger, more water-resistant and temperature durable

kerfing. Kerfing can also be concealed Wood will be bent along the grain

Adhesive applied to inside surfaces

Wood clamped onto single sided mold

with thick veneer.

adhesives, lighter and more reliable

SOLID WOOD LAMINATING

structures can now be engineered in Costs

Typical Applications

Suitability

laminated wood and so greater creative

• Low tooling costs • Moderate unit costs

• Architecture • Engineering timber • Furniture

• One-off to medium volume production

opportunities have arisen in design and

Plug (upper mold)

be formed using solid wood laminating.

Therefore this process is generally

architecture.There are 3 main areas of

used to strengthen a section of timber

wood lamination: solid wood, wood chip Quality

Related Processes

Speed

and veneer lamination.

• High

• CNC machining • Steam bending

• Medium to long cycle time (up to 24 hours)

Solid wood bending is a cold press process generally limited to a single

Only gradual and large radii bends can

by cutting it into sections and bonding them back together in the desired shape. Laminating reduces shrinkage,

Adhesive applied to inside surfaces

Veneers forced together under pressure

axis. It consists of bending sections of

twisting and warpage, which may be critical to a building project, for

wood and laminating them together with adhesive. It is typically used to

Breuer and the Eames, and more recently

constructions and metal processes. For

form structural elements for buildings.

the Azumis and BarberOsgerby, Veneers

example, light aircraft were once made

To make a tighter bend radii possible,

are laminated onto a single mold, with

from laminated veneers and are now

the wood can be kerfed, that is slots

the addition of a vacuum or split mold.

produced in high tech composites of

can be cut into the inside of the bend,

The adhesives are cured by low voltage

carbon, aramid, glass and thermosetting

perpendicular to the direction of bend.

h eatin g, radi ant h eati n g, radi 0 frequen cy

resins, as developments in technology

VENEER LAMINATING

Laminating then acts as a means of

(RF) or at room temperature,

have made this economically possible.

This is carried out in a number of

example. To maintain the balance

For certain applications, CNC

locking the bend in place. Kerfing is a

between tension and compression, the sections must be inverted on one another if they are cut from the same log, to avoid warpage post-forming.

ways, such as onto a single sided mold,

useful modelmaking technique, as bends

TYPICAL APPLICATIONS

machining (page 182) is an alternative to

with the addition of a vacuum, or in

can be formed in solid sections of wood

Depending on the adhesive, wood

wood laminating. Steam bending (page

a split mold. All use the same basic

or in plywood without high pressure or

laminating processes can be used to

198) can be used to form solid timber.

principle of laminating an odd number

even tooling. Sheets precut with kerfing

produce articles, such as furniture and

A combination of these 2 processes is

of veneers (plies) perpendicular to

already exist for this purpose,

architectural products, for use both

frequently employed to achieve greater

each other, as seen in plywood, with

indoors and outdoors.

flexibility in manufacture.

Wood chip techniques are often used

adhesive under pressure. The wood

is the matrix for the adhesive, which

Wood chip and solid timber

to produce engineering timbers (page 465) for architectural applications such

applications include engineering timber

QUALITY

as load bearing beams, trusses and eaves.

products such as trusses, beams and

The quality of afinished wood laminated

The products are manufactured using

eaves, while veneer laminating and

article is high, although the parts

high pressure and penetrating adhesives

kerfing are used to produce an array of

to bond the wood chips permanently.

products that include seating, storage

often require finishing operations and sanding. The integral quality of the parts is determined by the grade of timber and strength and distribution of the

essential to ensure that the part does

adhesive. Working with timber requires a

not warp. Sheets are laminated this

Veneer lamination is an exciting

and room dividers.

process for designers, and over the years

determines the lamination strength.

Adhesive is applied to the face of each veneer as it is laid on top of the last. The lay-up is symmetrical, with a core made up of an uneven number of plies and face veneers of a similar material and equal thickness. This is

it has been used a great deal in the

RELATED PROCESSES

furniture industry by designers such

Veneer laminating has been replaced

skilled workforce, and these processes are

way to improve their resistance to

as A1 var Aalto, Walter Gropius, Marcel

over the years by other composite

no exception.

shrinkage, warpage and twisting.

Case Study

Veneer laminating preparation The method of preparation is the same for all of the veneer laminating processes. Face veneers are 'bookmatched' or

The core veneers, which are often birch

of a lower grade, are rotary cut (peeled) from a log. Much larger sheets can be

'slipmatched', depending on the grain of the

produced this way than by slicing across

wood. Slipmatching means taking veneers

the width of the log. They are cut to size

from the log and placing them next to one

on a guillotine (image 3). Each layer of

another. In bookmatching the veneers are

veneer is coated with urea-formaldehyde

opened next to one another (like a book) to

(UF) glue (image 4) and then stacked in

create a symmetrical and repeating pattern.

preparation for laminating.

Complex and curving grain is generally bookmatched to avoid it looking too 'busy', whereas straight grained wood is often slipmatched. In this case study the face veneers have

been bookmatched (image i).They are

o o The minimum internal radius is

COSTS

side with a continuous glass filament

developed a unique bending and layering technique that makes it possible

determined by the thickness ofthe

Toolin g costs are 10w to moderate for

coated with a hot melt adhesive (image 2).

to produce much deeper dish profiles.

individual veneers, rather than by the

wood laminating. Wood-based products,

number of veneers or thickness ofthe

such as oriented strand board (OSB)

then stitched together on their reverse

This join needs to hold in place only until the veneers are permanently bonded during lamination.

Cur ve d form s m ade by 1 am in ati n g have minimal spring-back, unlike

Cutting wood into strips, or veneers, and bonding it back together

build.This means that even parts with

and plywood, as well as solid timber can be used to produce molds, which often

greatly improves its strength and

large wall thicknesses can be formed

resistance to shrinkage, twisting and

to tight internal radii. Each veneer is

last for several hundred products. For

warpage. Applying a simple curve

typically between 1 mm and 5 mm

high quantities the wooden molds are

to a structure further improves its

(0.04-0.2 in.) thick,

replaced with aluminium or steel ones.

COMPATIBLE MATERIALS

depends on the adhesive curing system,

Although cycle time can be long, it

strength characteristics.

those made by steam bending, and are

z



The pulp stock is a mixture of 1.4%

In stage 3, the pulp shell is demolded

machine than aluminium. The transfer

pulped paper and water. In stage 1, it is

tool places the pulp shell, which is now

stirred constantly to maintain an even

only 75% water and self-supporting, onto

mixture as the tool is dipped in it. The

a conveyor belt. The shell is then warmed

molding is formed over the tool by a

and dried in an oven for about 15 minutes.

The primary use of paper pulp molding

vacuum, which draws water from the pulp

Alternatively, it is pressed into a hot tool

is for packaging. There are a couple of

stock, and in doing so begins to dry out

that dries it out rapidly.

exceptions, including biodegradable

the pulp shell that forms over it. The tool

flowerpots and even a lampshade.

is dipped in the stock long enough for it to

RELATED PROCESSES Molded expanded polystyrene (page 432), thermoforming (page 30) and die-cut corrugated card (page 266) are all used

pulp moldings are generally accurate to

tools to accommodate the progressively

within o.i mm (o.oo4in.).They can also

shrinking pulp molding.

for similar applications. As well as its

be made resistant to grease and water

environmental benefits, paper pulp has

with an additive known as 'beeswax'.

many other advantages; it is lightweight,

The smoothness of the molding is

DESIGN OPPORTUNITIES The main advantage of paper pulp

improved by wet pressing or hot pressing

molding compared to the related

molded (increases versatility) and

in the drying cycle. With such techniques

processes is its environmental impacts.

relatively inexpensive.

logos and fine text can be embossed

Essentially, paper pulp packaging is

into the molding. Alternatively, parts

board formed into sheet geometries. It

cushioning and protective, anti-static,

steel mesh.

Above Cull-U N packaging is UN certifiedforthe transportation of

Middle

The contents, in a

Top The face oftilis tool is covered with stainless

hazardous chemicals.

QUALITY

can be hot pressed in the final stage

is therefore typically not an added value

The tool is covered with

cardboard box, can be

Paper pulp is made up of natural

of air drying.This technique is a cost

material. However, it can be coloured

holes, for water to be

ingredients and so by its very nature

effective alternative to conventional hot

and printed, foil blocked and blind

is a variable material. Even so, paper

pressing, which requires up to 4 sets of

embossed. It is naturally grey or brown.

drawn through it and a pulp molding to form.

dropped onto a steel plate from 1.4m (4.6ft), without breaking.

Case Study

Molding paper pulp packaging The corrugated card waste produced in

pulp shell is demolded into a transfer tool.

1 side of Culler Packaging's facility is raw

The role of the transfer tool is to place

material in the paper pulp production

the fragile pulp shell carefully onto the

plant (image i). A predetermined quantity

conveyer (image 6).

is loaded into a vat, mixed with water and

The pulp moldings are fed into a gas

pulped gradually with a rotating paddle.

heated oven (image 7). Hot air (2000C/

The process is carried out slowly to avoid

392°F) is gently circulated around the

shortening the fibre length of the pulp.

moldings to dry them out. After 15 minutes

The pulp stock, which is 4% water, is

or so, the completed pulp shells are stacked

fed through a series of vats that remove

onto a pallet for shipping (image 8).

contamination and condition it in preparation for molding (image 2), The tools are mounted on a rotating arm, and usually work in tandem (Image 3). It is important that the tools all require roughly the same mass of pulp to

for the part when it is both wet and

maintain even distribution of pulp in the

dry. This is especially important for air

stock. The tools are dipped into the stock

dried moldings, which have to be self-

for about 1 second (image 4), after which

supporting within seconds of forming,

they emerge coated with a rich brown

because they are deposited onto a

layer of pulp (image 5). The partially dry

conveyor belt while still having at least 75% water content.

When fully dry, any ribbing provides depending on the stock. Brown pulp is

added support for the package contents,

typically made up ofhigh quality craft

including cushioning, strength and a

paper, whereas grey pulp is composed of

friction fit.

recycled newsprint and is not as sturdy or resilient as brown pulp.

Air dried moldings will have 1 smooth side (the tool side) and 1 rough one.The rough side will not show fine details that

Material thickness can range from i mm to 5 mm (0.04-0.2 in.), depending on the design needs. Pulp moldings can be up to 400 x 1,700 mm (15.75 x 66.92 in.) and 165 mm (6.5 in.) deep. Vertical

have been reproduced on the smooth

dipping machines can make products

side. Wet pressing improves surface

deeperthan 165 mm (6.5 in.).

COMPATIBLE MATERIALS

require additional tooling. As the pulp

ENVIRONMENTAL IMPACTS

Draft angles are especially important

This process is specifically designed for

molding dries it shrinks, and so for

This process for disposable packaging has

finish and reduces permeability. Logos,

for this process.The tools come together

molding paper pulp. It can be industrial

hot pressing several sets of tools are

admirable environmental credentials,

instructions and otherfine details can be

along a single axis and there is no room

or post-consumer waste, or a mixture of

sometimes required. Each set of tooling

because it uses ioo% recycled material,

pressed into a partially dry molding.

for adjustment. The molded part must

both of these.

roughly doubles the initial costs.

which can be recycled again and is fully

finish. And hot pressing improves surface

therefore be extracted along that axis.

DESIGN CONSIDERATIONS

It is possible to mix in other fibres,

Cycle time is rapid. Some machines

biodegradable. In the above case study

Draft angles are usually 50 on each

such as flax, with the waste paper

can operate at up to 10 cycles per minute.

from Cullen Packaging, the paper pulp

Paper pulp is made up of cellulose wood

side,but will depend on the design of

material, to reduce further the

However, it is more common to mold

is made up of by-product from their

fibres bonded together with lignin (the

the molding. It must be remembered

environmental impact of the product.

around 5 parts per minute.The drying

corrugated card production facility next

2 main ingredients of wood itself). No

that, when extracted from thetool,the

Additional fibres will affect the aesthetics

time extends the cycle time, adding

door, diverting it from landfill.

additional adhesives, binders or other

molded part comprises up of 75% water

and strength of the part.

ingredients are added to strengthen this

and so is very supple.

natural composite material.Therefore,

The parts are typically stacked onto a

COSTS

the wall thickness is increased and ribs

pallet and,because of the draft angle, the

Tooling costs are generally low but

are designed in for added strength.

parts can be packed more densely, saving

do depend on the complexity of the

The ribbing provides added strength

on costly transportation expenses.

roughly 15 minutes to the process. Hot pressing is quicker.

molding. Wet pressing and hot pressing

Labour costs are relatively low because most operations are automated.

Waste produced by th e process can be directly recycled and averages 3%. Water used in production is continuously recycled to reduce energy consumption.

Featured Manufacturer

Cullen Packaging www.cuUen.co.uk

Forming Technology

Composite Laminating Strong fibres and rigid plastics can be amalgamated to form ultra lightweight and robust products, using composite laminating. A range of material combinations is used to produce parts that are suitable for the demands of high performance applications.

INTRODUCTION

are used to apply heat and pressure

Composite laminating is an exciting

during the curing phase.

range of processes that are used in the

Pre-preg is the most expensive

construction of racing cars, aeroplanes

composite laminating process, and

and sailing boats alike.

therefore is limited to applications

There are 3 main types of laminating:

where performance is critical. It is made

wet lay-up, pre-preg (short term for

up of a mat of woven reinforcement

o o

pre-impregnatedwith resin) and resin

with resin impregnated between the

T3

Costs

Typical Applications

Suitability

transfer molding (RTM) (also known

fibres. The quantity of resin is precise, so

• Moderate to high tooling costs • Moderate to high unit costs, determined by surface area, complexity and performance

• Aerospace • Furniture • Racing cars

• One-off to batch production

as resin infusion).The resins used are

each layer of the lamination provides

Quality • High performance lightweight products

Related Processes • DMC and SMC molding • Injection molding • Thermoforming

Speed • Long cycle time (1-150 hours), depending on complexity and size of part

2:

O

structural framework in aeroplanes,

typically thermosetting and so will cure

optimum performance.This reduces the

satellite dishes, heat shielding, bicycle

at room temperature. In wet lay-up they

weight and increases the strength of the

frames, motorcycle parts, climbing

are soaked into woven mats of fibre

product, which is cured under pressure in

reinforcement, which is draped into a

an autoclave.

mold. For precision products, autoclaves

equipment and canoes.

Top left

strength to weight

Nomex® honeycomb

properties.

core is used to increase

the strength and bending stiffness of

Above

composite laminates.

aerodynamic racing

Above Left

car spoiler is made by CNC machining PUR

A lightweight

RELATED PROCESSES

Nomex® honeycomb

foam and encasing it in

manufacturing. Unit price is reduced

Composite laminating is unequalled in

core is laminated into

carbon fibre reinforced epoxy resin.

by accelerated production as a result of

its versatility and performance. Processes

Kevlar® aramidfibre epoxy for exceptional

using split molds, heat and pressure and

that can produce similar geometries

dividing the labour force into specialized

include dough molding compound

resistance and rigidity. Laminates cured

(DMC) and sheet molding compound

under pressure have the least porosity.

RTM is used for larger volume

areas of production.

(SMC) (page 218), injection molding

TYPICAL APPLICATIONS

(page 50) and thermoforming (page 30).

Processes other than RTM use single

sided molds, which produce a gloss finish

Until recently composite laminating

Metalworking processes that are used

on onlyi side. However, by joining two 3D

was limited to low volume production.

to produce the same geometries include

sheet geometries together a 3D hollow

However, since the development of RTM

part is made with an all over molded

finding application in the production of

panel beating, superforming (page 92) and metal stamping (page 82). DMC and SMC bridge the gap between injection molding and

automotive parts and bodywork and in

composite laminating.

it is now possible to make thousands of identical products.These processes are

finish. The surface finish of wet lay-up

and RTM products is improved by using a gel coat.

DESIGN OPPORTUNITIES

the aerospace Industry.

QUALITY

These versatile processes can be used

The mechanical properties of the product

for general-purpose glass fibre products

products, due to high costs. However,

are determined by the combination of

or high performance application with

designers have long craved the immense

materials and lay-up method. All of them

carbon and aramid fibre.The materials

potential of carbon fibre and other

produce products with long strand fibre

and method of lamination are selected

Manual laminating processes are

generally limited to high performance

composites, and so occasionally it is used

reinforcement.The resins used include

according to the budget and application,

for domestic products such as furniture.

polyester, vinylester, epoxy, phenolic and

which makes these processes suitable

Fibreglass is much cheaper and often the

cyanate.They are all thermosetting and

for a wide range of prototyping and

material of choice for such applications.

so have cross-links in their molecular

production applications.

High performance applications

structure. Thismeanstheyhavehigh

Fibre reinforcement is typically glass,

include the production of racing cars,

resistance to heat and chemicals as well

carbon, aramid or a combination. Various

boat hulls and sailing equipment.

as very high fatigue strength, impact

weaves are available to provide different

ffi H m

r~

>

§

Z CD

Lay-Up Processes Wet lay-up Single sided tool

Combination of fibre reinforcement and thermosetting resin

of 4.H bar (60 psi) and a temperature of

mold. When closed, resin is Injected under

balance of resin to fibre reinforcement.

120°C (2^8°F) for 2 hours. The pressure

pressure. Alternatively, the resin can be

are wet lay-up, pre-preg and resin transfer

Rollers are used to remove porosity.

and temperature are lowered when core

drawn through the mold under vacuum

materials are used.

(resin infusion) or it can simply be poured

All types of weave and thermosetting

framework

Demolding

Molding

Pre-preg lay-up Intermediate layer: breathable

is needed because this would Increase

known as 'double A side'. The molds are

process, gel coats are required for glass

methods. The mold is single sided and is

weight; Instead, the carbon fibre Is cut to

typically made from metal. Small molds

fibre products. For high volume production

made up of a skin of the composite material

predetermined patterns, which are laid Into

are machined from solid. Molds larger than

a thermoplastic-thermosettlng combination

supported by a rigid framework. It is

the pre-preg mold. Because the fibres are

1 m3 (35.31 ft3) are typically electroformed

is used, which produces a very high quality

essential that the mold Is not only strong

sticky, they can be rubbed together to form

because at this size this process Is less

finish because as the thermosetting resin

and supportive during lay-up, but is also

a lamination that is free of porosity.

expensive than machining and is capable of

cools and shrinks the thermoplastic takes Its

producing parts with a surface area up to

place and forms a Tow profile' surface finish.

the Intermediate layer Is a breathable membrane. These 2 are sealed in with a

prior to lamination. Gel coats are anaerobic;

These layers ensure that an even vacuum

in other words, they cure when not in the

can be applied to the whole surface area,

presence of oxygen, which is ideal for the

because if a vacuum was applied under 1

thermosetting resin is painted or sprayed

Finished workpiece

a blue film, which is permeable, while

hermetic film, and a vacuum is applied.

are laid onto the gel coat, and then

Air escapes through split line

with 3 layers of material. The first is

or sprayed onto the surface of the mold

Mats of woven fibre reinforcement

Moving platen

After lay-up the whole mold Is covered

(the same as in lamination), which is painted

mold face.

Resin transfer molding

areas that need density of material, such as surrounding a racing driver's head. Surface area is limited to 16 m2

(172 ft2), although it is possible to make larger products in more than i piece. Molding

Demolding

Monocoque boat hulls,for example, are made in stages-each area being

Because RTM Is basically a wet lay-up

16 m2 (172 ft2). The molds are preheated, then the

fibre reinforcement is laid into the open

layer of film It would stick and air pockets would be left behind.

ItiWi

The pre-preg lay-up is placed into an autoclave, which is raised to a pressure

Left above fibre chop strand mat is

Right above Unidirectional glass fibre weave has

used in wet lay-up and

specialized uses.

General purpose glass

Static platen

In prior to molding.

is the least precise of all the laminating

coat. The gel coat is a thermosetting resin

Demolding

RTM uses matched molds to produce

parts with a high quality finish on both sides,

Wet lay-up is typically started with a gel

Molding

precise and expensive. It Is most commonly used to form carbon fibre. No gel coat

be removed post-curing.

Skin of 6-8 mm j (0.236-0.315 in.) '

Pre-preg lay-up is more time-consuming,

resin can be applied by wet lay-up, which

sufficiently flexible to allow the molding to Valves

Pre-preg carbon fibre

onto it. It is important to achieve the right

The 3 main types of composite laminating molding (RTM).

Rigid j

Inner layer: permeable blue film"

TECHNICAL DESCRIPTION

resin transfer molding.

Right below Left below Carbon fibre twill is a high performance

very good resistance to

weave material.

high temperatures.

Kevlar® aramid and

epoxy composite has

laminated and cured one at a time. Manual lay-up methods are labour strength characteristics.The direction

DuPont™ Nomex® honeycomb (their

intensive and expensive. Each product

time-consuming process.To maximize

include plain (known as 0-90), twill

of weave will affect the mechanical

trademark for aramid sheet), foam and

may have between 1 and 10 layers of

strength, each layer of the lamination is

and specialist (see image, above right).

available only as spun fibres or sheet

properties of the part. For high

aluminium honeycomb (see images,

fibre reinforcement, and each layer is

overlapped at a different point to create

Forlarge surface areas chopping and

material because there is no other

performance products this is calculated

page 207). Cores make step changes in

applied by hand. A complex product may

astaggeredlap joint.

wall thickness possible.

be constructed from 10s of parts, which

using finite element analysis (FEA) prior

makes it very expensive.

to manufacture. Certain weaves have better drape and so can be formed into

DESIGN CONSIDERATIONS

Molds should be made from the same

COMPATIBLE MATERIALS Fibre reinforcement materials include

trademark name Kevlar®. Aramid is

spraying the glass fibres directly onto

practical way to make it. It has very high

the mold's surface produces a similar

resistance to abrasion and cutting, very

material to chop strand mat.

high strength to weight and superior

Carbon fibre has higher heat

temperature resistance.

Carbon and aramid fibres are very

materials as the part to be laminated.

fibreglass, carbon and aramid.

resistance, tensile strength and durability

is critical; just 50 of movement will

expensive, so every effort should be taken

This will ensure that the molds have

reduce its strength by 20%.

the same coefficient of expansion as

Glass fibre is a general purpose laminating material that is heat

than glass fibre. When combined with a

to minimize material consumption while

precise amount of thermosetting plastic

automotive industry there have been

Core materials are used to increase

maximizing strength. Wall thickness

the materials. Wall thickness is typically

resistant, durable and has good tensile

it has an exceptional strength to weight

many significant improvements in

the depth of the parts and thus increase

is limited to 0.25-10 mm (0.01-0.4 in.)

6 mm to 8 mm (0.236-0.315 in.).

deeper profiles. However, fibre alignment

When the mold parts are joined

Since composite laminating has become more important in the

strength. It is relatively inexpensive and

ratio, which is superior to steel. Carbon

materials such as a material that is made

can be used for a range of applications.

fibre twill (see image, below left) is the

up of glass fibres and polypropylene

most common weave.

torsional strength and bending stiffness.

(any thicker and the exothermic reaction

The role of the core material is to

can be too dangerous). Carbon fibre is

together, the fibre reinforcement is

Non-woven materials are the least

maintain the integrity of the composite

generally between 0.5 mm and 0.75 mm

overlapped.The case studies illustrate

expensive and known as chop strand

skin. Examples of core material include

(0.02-0.03 in.) and is only ever built up in

2 methods for doing this skilful and

mat (see image, above left). Weaves

Aramid fibre (see image, below right) is commonly referred to by the DuPont™

(PP) woven together.The composites are loaded into a heated mold and pressed,

which causes the PP to melt and flow

Far left PP and glass fibre have been woven together

Left Rigid molded glass fibre reinforced PP panels

into a novel composite

such as this have begun

material, which can

to replace sheet metal in

then be formed into rigid, lightweight panels

the automotive industry.

using resin transfer

molding technology.

around the glass fibre reinforcement (see

hour or so, whereas a large one with

contact with the materials and potential

images, page 216, above).

lots of undercut features and cores may

health hazards.

require as many as 150 hours.

COSTS

Labour costs are high because

Material developments are reducing the environmental impact of the process.

Tooling costs are moderate to high,

composite laminating is a skilful and

For example, hemp is being researched

as moldmaldng is a labour intensive

labour intensive process.

as an alternative to glass fibre, and in

complexity of the product. The tooling is

ENVIRONMENTAL IMPACTS

thermosetting materials.

done in the same way as the laminated

Laminated composites reduce the

process. Cost depends on the size and

some cases thermoplastics are replacing

product. Therefore, a master (pattern)

weight of products and so minimize

has to be made. However, it is possible to

fuel consumption. However, harmful

form th e m ol d from al m ost any m ateri al

chemicals are used in their production

and then fill, spray paint and polish the

and it is not possible to recycle any of the

surface to produce the required finish.

offcuts or scrap material.

Cycle time depends on the complexity of the part. A small part might take an

Operators must wear protective clothing in order to avoid too much

Case Study

Wet lay-up for the Ribbon chair The Ribbon chair (image 1) was designed This agent stops the gel coat bonding with by Ansel Thompson in 2002. It is the surface of the tool. constructed with vinylester, glass and The flanges are taped to enable the mold aramid reinforcement, and a polyurethane to be closed (Image 4), then the gel coat foam core, in a lengthy process that takes is applied and the masking tape removed approximately 1 day. The sequence of events (images 5 and 6). are; mold preparation, release agent, gel coat, lamination, cure time, demolding and

then finishing. The mold is prepared before each molding (image 2). Because the chair is a complex shape, the mold is designed to come apart to make demolding easier.

Particular care is taken in preparing the surface finish because it will be reflected on the outside surface of the part. Once the parts have been assembled, a wax release

agent is applied with a soft cloth (image 3).

The glass and aramid fibre mat is cut

The molds are then brought together

into patterns to fit the chair, using i of

and bolted along the flange (image 12).

2 different types of fibre reinforcement

Excess resin squeezes out as the bolts

(image 7). Sheets of fibre are laid onto the

are tightened. The design of the mold

gel coat, and vinylester is applied to the

means that an overlap of material forms

back (image 8). Air is then removed with a

a strong joint. While clamped shut an

paddle roller (image 9).

expanding polyurethane (PUR) foam is

The layers are gradually built up, and

injected into the mold cavity. This forces

care is taken to ensure that joints do not

the lamination against the surface of

overlap and cause weaknesses (image 10).

the mold, in order to improve the surface

An area of aramid is then applied to the

finish. It also increases the strength of the

inside of the seat, to increase resilience

chair by supporting the thin composite

and strength (image n).

wall sections.

After about 45 minutes the vinylester is fully cured and the mold is separated (image 13). it is trimmed and polished to complete the process (image 14).

9

Featured Manufacturer Radcor IO

11

www. rad cor. co.uk

Case Study

Case Study

Racing car design with carbon fibre

Pre-preg carbon fibre lay-up for the roll hoop trailing edge

Pre-preg carbon fibre is used in the

This case study demonstrates the production

roll hoop trailing edge, which is made with

like an x-y plotter (image 2).The carbon fibre

production of high performance racing

per gram (0.035 oz) of carbon fibre. The

of a small piece of the Intersport Lola B05/40

a simple split mold, so is relatively simple.

is coated with plastic film on either side. This

cars such as the Lola B05/30 Formula 3 car

image shows how the carbon has shattered

racing car (image 1). In total, this car is made

Parts such as the monocoque structure (see

Is peeled off just prior to lay-up (image 3).

{image 1), which is manufactured by Lola Cars.

into fragments. Each of the fragments is

up of hundreds of carbon fibre components.

opposite) comprise many different pieces,

The mold is In 2 parts (image 4), which are

Production starts when the designers

cured at different stages and incorporates

laid up separately. The carbon fibre patterns

Success is measured in energy absorption

Construction (image 2) is closely tied into

absorbing a small amount of the Impact;

design and engineering. High performance

so the smaller the fragments, then the

complete the 'lay-up handbook', which

core material. The lay-up handbook ensures

are aligned on the part with the rubbed side

products have to be engineered to take

more successful the engineering design.

outlines the production requirements of

that each part is made according to the

downwards (image 5). Each i Is trimmed

Exact replicas of the cars, Including

each part, including pattern profile, number

design requirements.

carbon fibre wheels, are tested at 50%

of laminations and sequence of production.

scale in a wind tunnel (image 6). This

This case study covers the production of the

the maximum load,yet be as lightweight as possible. It is the role of a carbon fibre engineer to push carbon fibre to its limits. The process of designing and producing a car takes approximately 8 months. By using detailed design, FEA and controlled testing, parts can be produced directly from the CAD drawing. In the CAD drawing of the monocoque chassis on

the car (image 3), FEA software is used to determine the stresses and strains

on the structure (image 4). This helps the engineer to calculate the optimal structure within set parameters.

Critical parts are molded and tested to ensure that the calculations are correct. A crash test is simulated on the nose cone of the car-the average deceleration

being 25G during impact (image 5). The aim of this part is to deaccelerate the car in a head-on collision.The nose cone is

coloured yellow and is attached to the monocoque structure.

Featured Manufacturer Lola Cars International www.lolacars.com

The patterns of carbon fibre are fed through to a kit cutter, which functions much

(image 6), leaving a small overlap to make a stronger joint interface, before the next layer is applied.

helps to solve issues of aerodynamics, balance and tuning.

o o

a pale pink hermetic film (image 13). The

produce the complete car. All of the parts are

in exactly the same way. Each pattern of

resulting 'sandwich' enables a vacuum to

finally brought together and assembled to

carbon fibre is cut to fit the mold like a dress

be applied on the mold, which forces the

make up the complete car (image 18).

(image 7). Profiled 'dobbers' are used to rub

laminate onto its surface (image 14).

The second part of the mold 1s kid up

the weave into tight corners (image 8). Three

The vacuumed mold is then placed in

layers of carbon fibre are applied to each

an autoclave (image 15), which cures the

surface, and the 2 halves of the mold are

resin with heat and pressure. The size of the

brought together (image 9). The layers are

autoclave limits the size of part - larger parts

carefully overlapped in the joint with another

are restricted to oven or room temperature

dobber (image 10).

curing methods.

When all the layers are in place the entire molding and tool are covered with

Many molds are placed in the autoclave at 1 time because curing is a 2 hour process.

a permeable blue film (image 11). This is

When finished, the part is removed (image

overlaid with a layer of breathable membrane

16). At the Lola Cars workshop (image 17), up

(image 12). The mold is then placed inside

to 20 laminators may be working at 1 time to

Compression Molding DMC Process

Hydraulic ram

Compression molding is used to form dough molding compound Locating pin

(DMC) and sheet molding compound (SMC) into structural and

Static platen

lightweight parts. These processes bridge the gap between

Ejector pins

composite laminating and injection molding.

Typical Applications

Costs • Moderate tooling costs • Low unit costs (3 to 4 times material

• Automotive • Building and construction • Electrical and telecommunication

Stage 1: Load

RELATED PROCESSES

TECHNICAL DESCRIPTION

• Medium to high volume production

Similar products can be made by

The diagram illustrates compression

process that ensures even distribution of

injection molding (page 50) and

molding DMC. SMC is a similar

material throughout the die cavity.

composite laminating. Reinforced

process, except that it is used for sheet

injection molded products are

profiles as opposed to bulk shapes.

Related Processes

Speed

• High strength parts with long fibre length

• Composite laminating • Compression molding • Injection molding

• Cycle time between 2-5 minutes

structurally inferior because the length

The molding compound is a mixture of

cured when it reaches 150°C (302°F)(

fibre reinforcement and thermosetting

which takes 2-5 minutes. In stage 3, the

resin; DMC is made up of chopped fibre

parts of the mold separate in sequence.

QUALITY

reinforcement, whereas SMC contains

If necessary, the part is relieved from the

sheets of woven fibre reinforcement.

lower or upper tool with ejector pins.

SMC: the raw materials are available

fatigue.These qualities make DMC

Combined with compression molding,

with different weave patterns for

and SMC very useful in electrical and

DMC and SMC have been used to replace

different structural applications.This

telecommunication applications. Some

to the materials such as heat resistant

steel and aluminium in applications

has significant mechanical advantages,

examples include enclosures, insulating

and electrically insulating polyester or

such as automotive bodywork and

similar to those of laminated composites

panels and discs.

phenolic.Thermosetting plastics are

(page 206).

The high volume, high strength and lightweight characteristics of DMC and

more crystalline and as a result are more acids and other chemicals.

A similar process, called pultrusion,

This is a very high quality process. Many of the characteristics can be attributed

resistant not only to heat, but also to

reinforced thermosetting materials

is used to produce continuous

SMC make them suitable for automotive

such as polyester, epoxy and phenolic

lengths of fibre-reinforced plastic.

parts. Examples include body panels,

resin. DMC is also referred to as BMC

Instead of compressing the materials,

seal frames and shells, engine covers

detail is very good. The compression, rather than injection, of material in the

Surface finish and reproduction of

(bulk molding compound).There are

pultrusion draws fibre through abath

and structural beams. Electric cars are

thermoplastic alternatives such as GMT

of thermosetting resin, which cures

making use of these materials because

die cavity produces parts with reduced

(glass mat thermoplastic), which is a

to form a continuous profile similar

they combine mechanical strength with

stress that are less prone to distortion.

DESIGN OPPORTUNITIES

fibre reinforced polypropylene (PP). Other

to extrusion. Pultrusion is the bridge

types of reinforcement include aramid

between filament winding (page 222)

high dielectric strength. In the building and construction

and carbon fibre. In recent years natural

and extrusion for continuous profiles.

sector, DMC and SMC are suitable for door pan el s, fl oorin g an d roof coverin g

TYPICAL APPLICATIONS

materials.They are very durable and so

the requirements of the application.This

to reduce the environmental impact of

These materials can be mass-produced

are suitable for public space furniture

helps to reduce weight and maximize the

these materials.

and so are suitable for application in a

and signage.

efficiency of the process.

as hemp, have been trialled in an attempt

DMC is compression molded to form bulk shapes. In contrast, SMC is

range of industries. Thermosetting composite materials

compression molded to form lightweight

have high resilience to dielectric

sheet components with a uniform

vibration, high mechanical strength

wall thickness. Fibre length is longer in

and are resistant to corrosion and

The sequence of operation is the same

for both and includes loading, molding

Metal inserts and electrical

It is a simple operation but is suitable for the production of complex parts.

and de-molding. In stage 1, a measure of

It operates at high pressure, ranging

DMC or SMC is loaded into the die cavity in

from AO to 400 tonnes UA-WI US tons),

the lower tool. Metal inserts with locating

although 150 tonnes (165 US tons) is

pins are loaded into slots. They are in

generally the limit. The size and shape

line with the direction of ejection because

of the part will affect the amount of

otherwise the part would not release

pressure required. Greater pressures

from the mold.

will ensure better surface finish and

In stage 2, the upper tool is gradually

reproduction of detail.

forced into the die cavity. It is a steady

DESIGN CONSIDERATIONS The type of fibre reinforcement and length of strand can be modified to suit

materials with suitable properties, such

Thermosetting material plasticizes at approximately 115°C (239° F) and is

of the fibre is considerably shorter.

INTRODUCTION

DMC and SMC are typically glass

Stage3: Finish

Suitability

Quality

structural electronic enclosures.

Stage 2: Mold

The size of the part can be 0.1-8 kg

Colours are applied by spray painting (page 350) because the thermosetting resins in DMC and SMC have a limited

the pressure that can be applied across

colour range.

the surface area, which is affected by part

(0.22-17.64 lb) on a400 tonne (441 US

ton) press.The dimensions are limited by

As with injection molding, there are

g eom etry an d design. An oth er m aj or

many design considerations that need

factor that affects part size is venting

to be taken into account when working

gases from the thermosetting material

components can be over-molded.This

with compression molding. Draft angles

as it cures andheats up.This plays an

reduces secondary operations.

can be reduced to less than o.50,if both

important role in tool design, which aims

the tool and the ejector system are

to get rid of gasses with the use of vents

designed carefully.

and clever rib design.

Step changes in wall thickness are not

a problem with DMC molding.

o > z a en 2 o S o r* a

Case Study

Compression molding 8-pin rings This is a DMC compression molding

After curing, the molds separate to reveal the

operation. In preparation, the metal inserts

fully formed part (image 5). The locating pins

are screwed onto locating pins (image 1). The

attached to the metal inserts remain on

surface of the metal inserts are knurled to

the part as it is removed (image 6).

increase the strength of the over-molding. The

from the metal inserts (image 7) and

Inserts are also loaded into the lower tool.

the workpiece is de-flashed by hand

A pre-determined weight of polyester and

(image 8). The finished moldings are

glass based DMC is loaded into the die

stacked (image 9).

(images 3 and 4). The 2 halves of the die come together to force the polyester to fill the die cavity.

Wall thickness can range from i mm to 50 mm (0.04-1.97 in.)-It is limited by the

COMPATIBLE MATERIALS

COSTS

Thermosetting materials molded in

Tooling is generally less expensive than

i7o0C and i8o0C (338- 3560F). It is not

molding temperatures, typically between

exothermic nature of the thermosetting

this way include polyester, epoxy and

for injection molding because less

possible to recycle them directly due

reaction because thick wall sections are

phenolic resin.Thermoplastic composites

pressure is applied and the tooling tends

to their molecular structure, which is

prone to blistering and other defects as a

are generally polypropylene; the molding

to be simpler.

cross-linked.This means that any scrap

direct result of the catalytic reaction. It is

process for these is different because

generally better to reduce wall thickness

they have to be plasticized and formed.

and minimize material consumption, so

Fibre reinforcement can be glass,

Cycle time is 2-5 minutes, depending

on the size of the part and length of time

produced, such as flash and offcuts, has to be disposed of.

it takes to cure. Labour costs are moderate because

bulky parts are hollowed out or inserts

aramid, carbon or a natural fibre such

are added. However, some applications

as hemp, jute, cotton, rag andflax. Other

the process requires a great deal of manual input.

require thick wall sections such as parts

fillers include talc and wood.The various

that have to withstand high levels of

fibre reinforcement and filler materials

dielectric vibration.

are used to increase the strength,

ENVIRONMENTAL IMPACTS

durability, resistance to cracking,

The main environmental impacts

dielectric resilience and insulating

arise as a result of the materials used.

properties of the part.

Thermosetting plastics require higher

The locating pins are unscrewed

pins are loaded into the upper tool (image 2).

Featured Manufacturer Cromwell Plastics www.cromwell-plastics.co.uk

Forming Technology

Filament Winding Layers of carbon fibre monofilaments, coated in epoxy resin, are wound onto a shaped mandrel to give the ultimate strength characteristics. The mandrel is either removed and reused, or permanently encapsulated by the carbon fibres.

Costs

Typical Applications

INTRODUCTION

There are 2 main types of winding,

Filament winding is used to produce

'wet'and'pre-preg'. Wet winding draws

continuous, sheet and hollow profiles

the fibre tow through an epoxy bath

for applications that demandthe high

prior to application. Pre-preg winding

performance characteristics of fibre

uses carbon fibre tow pre-impregnated

reinforced composites.They are produced

by winding a continuous length of fibre

with epoxy resin, which can be applied directly to the mandrel without any

around a mandrel.The fibre 1s coated

other preparation.

Suitability

with thermosetting resin to produce

high strength and lightweight shapes.

TYPICAL APPLICATIONS

The fibre (typically glass, carbon or aramid) is applied as a tow that contains

in high performance applications in the

• Low to moderate tooling costs, depending on size • Moderate to high unit costs

• Aerospace • Automotive • Deep sea submersibles

• One-off to batch production

Quality

Related Processes

Speed

• High gloss surface finish • High performance, lightweight products

• 3D thermal laminating • Composite laminating • DMC and SMC molding

• Moderate cycle time for small parts (20-120 minutes); large parts may take several weeks

Fil am ent woun d products can be foun d

a set number of fibre monofilaments. For

aerospace, deep sea and automotive

example,i2l< tow has 12,000 strands,

industries. Some examples include

while 24k has 24,000 strands.

blades for wind turbines and helicopters, pressure vessels, deep sea submersibles, suspension systems, torsional drive

has an aluminium liner

Top CNC machining after filament winding

filament wound with

produces very accurate

RELATED PROCESSES

carbon fibre composite.

surface dimensions.

Filament winding is used to produce

Left The gloss surface finish is a gel coat resistant to

tapers on the outside surface are applied in

Above

shafts and structural framework for

This pressure vessel

aerospace applications,

Channels, recesses and

low volumes of cylindrical parts. Higher volumes can be produced by DMC and

this way.

heat or chemical attack.

SMC molding (page 218). Composite laminating (page 206) is used to produce similar profiles. The benefit of

filament winding is that the direction

QUALITY There are 4 main types of finish.These

Winding is computer guided, making it precise to 100 microns

of the strand can be adjusted precisely

are 'as wound', taped, machined and

(0.0039 in.). The angle of application

throughout production from almost

epoxy gel coat.'As wound'finishes have

will determine whether the layer is

o0 up to 90°. In composite laminating,

no special treatment. Taped finishes

filaments are woven into mats with

produce a smooth surface finish.The

providing longitudinal, torsional (twist) or circumferential (hoop) strength. Layers

intertwined warp and weft.

principle is the same as vacuum bagging

are built up to provide the required

The 3D thermal laminating (3DL, page 228) developed by North Sails is similar to filament winding.The difference is that

in composite laminating, but the surface

mechanical properties. Products cannot

finish is more controllable. Surfaces are

be interchanged between applications

machined where precise tolerances are

filaments are laid onto a static mold in

required (see image,top). Smooth, glossy

because their properties will be designed specifically for each.

a process known as tape laying. In this

finishes can be achieved with epoxy gel

case the molds can be very large and up

coat (see image,left).

to 400 m2 (4,305 ft2). 3DL is best suited to sheet parts, where as filament winding is more suitedto hollow parts.

Stiffness is determined by the thickness of lay-up andtube diameter.

DESIGN OPPORTUNITIES Opportunities for designers are limited to cylindrical and hollow parts. But they need not be rotationally symmetrical;

Filament Winding Process

Supply reel of carbon fibre

Guide head

Continuous length of carbon fibre tow

TECHNICAL DESCRIPTION The carbon fibre tow is applied to the

reinforcement is loaded. This is the wet lay-

several different angles of tow. depending

rotating mandrel by a guide head. The head

up process; the fibre reinforcement is coated

on the requirements.

moves up and down along the mandrel as it

with an epoxy resin by a wheel rotating in a

rotates, and guides the filament into the geodesic overlapping pattern.

bath of the resin.

A complete circuit is made when the

Bulges can be made by concentrating the tow in a small area. These are used either to create localized areas of strength or to build

guide head has travelled from 1 end of the

up larger diameters that can be machined

to the material being used and the layer

mandrel to the other and back to the starting

for accuracy.

thickness required.

point. The speed of the head relative to the

The width of the tow is chosen according

The fibre is continuous and only broken when a new supply reel of fibre

COMPATIBLE MATERIALS Types of fibre reinforcement include

The winding process is computerguided. Even so,there is ahigh level

speed of mandrel rotation will determine the

glass, carbon and aramid. An outline of

of manual input, so labour costs are

angle of the fibre. A single circuit may have

their particular qualities is given under

moderate to high.

composite laminating.

Resins are typically thermosetting and

ENVIRONMENTAL IMPACTS

include polyester, vinylester, epoxy and

Laminated composites reduce the

oval, elliptical, sharp edged and flat-sided

DESIGN CONSIDERATIONS

These products are typically used for

phenolics.Thermosetting plastics have

weight of products and so reduce fuel

profiles can be filament wound (see

This is a high cost process for low

demanding applications, so the liners

cross-links in their molecular structure,

consumption.

image above).

volumes. Increasing the volumes reduces unit cost. Even so, the materials are

are typically produced by electron beam welding (page 288) high-grade

which means they have high resistance to heat and chemicals. Combined with

clothing to avoid the potential health

can be removed and reused, while

expensive and so every effort is made

aluminium or titanium.

carbon fibres these materials have very

hazards of contact with the materials.

3-dimensional hollow products that

to reduce material consumption while

are closed at both ends can be made by

maximizing strength.

high fatigue strength, impact resistance and rigidity.

recycled, so scrap and offcuts have to be

Parallel-sided and conical mandrels

winding the filament tow over a hollow

Parallel-sided parts can be made

Winding over a hollow liner produces parts that have inward and outward facing corners such as a bottleneck

Operators have to wear protective

Thermosetting materials cannot be disposed of. However, new thermoplastic

liner, which remains as part of the final

in long lengths and cut to size.

profile. Even though it is possible, it is

COSTS

systems are being developed that will

product (see image, page 227, above).This

Conventional filament winding is

generally not recommended to wind over

Tooling costs are low to moderate.

reduce the environmental impacts of

technique is known as bottle winding

typically limited to 3 m (10 ft) long and up

outward facing corners with a radius

Encapsulating the mandrel will increase

the process.

and is used to produce pressure vessels,

to 1 m (3.3 ft) in diameter. However, much

of less than 20 mm (0.8 in.) because

the cost.

housing and suspension systems.

larger forms are produced by filament

product performance will be affected.

winding, such as space rockets, which

There is no lower limit on the radius for

minutes for small parts, but can take

may take several weeks to make.

inward facing corners.

several weeks for very large parts. Curing

Other than shape, the benefits of winding over a liner include forming a water, air and gas tight skin.

Winding over a liner will increase the cost of the process because a new liner is manufactured for each cycle.

Filament winding cycle time is 20-120

time is typically 4-8 hours, depending on the resin system.

Top

Above

Non-circular profiles

Ibis flywheel is made up of 3 parts: the inner lining is glass fibre and

are suitable for filament winding. Examples

include the blades for wind turbines and helicopters.

the other 2 layers are carbon fibre.

Case Study

Filament winding a racing propshaft These are used in cars to deliver power from

(image 1). Carbon fibre tow is supplied from

the engine to the wheels. Traditionally these

a spool (image 2). Many different spools can

(image 5). In this case the carbon fibre is

components are made from metal, but when

be running simultaneously for multifibre

sealed onto the mandrel with a plastic tape

problem when tow is laid at or close to go0

carbon composite is used it is possible to

composites or if more than 1 mandrel is

(itnage 5). The tape squeezes excess epoxy

mate weight savings of up to 65%, Finite

being wound at the same time.The fibres are

resin from the carbon and ensures a high

element analysis is used to determine

coated with epoxy resin as they pass over the

quality, smooth finish. The excess is cut off

the stress and strain on the product prior

wheel (image 3).

while it is uncured (image 7). This is so that

to manufacture.The results, seen in the

The angle of application ranges from go0

computer generated images, indicate the

to almost o0. The mandrel ends are tapered so

required angle of tow and number of layers.

that adequate tension can be pulled on the

They are a parallel section tube and so are made on removable and reusable mandrels

the mandrel can be removed once the composite has cured.

The filament wound assemblies are

tow without it slipping along the mandrel

placed into an oven, which cures the resin at

(image 4) at shallow angles; this is not a

up to 2000C (3920F) for 4 hours. The whole curing process takes 8 hours because the

temperature inside the oven is ramped up and down gradually. Small droplets of resin form on the surface of the tape

during curing (image 8).This is removed when the tape is peeled off. The cured composite is removed from

the mandrel (image 9). It is possible to remove long cylinders from mandrels because metal expands and shrinks more

than carbon fibre, so is slightly smaller once it has cooled.This provides just enough space to remove the mandrel.

The ends of the shaft are cut off to precise tolerances, and machined metalwork is assembled onto the ends

(image io). These are bonded in with adhesives, which are heat cured.

1. .

Hi r.^

Continuous

Bend

Bulk

Internal

Forming Technology

3D Thermal Laminating This technology was developed by North Sails to make ultra lightweight, seamless 3-dimensional sails. The fibre reinforcement is continuous over the entire surface of the sail,

Fibre layouts Any combination of

fibre include aramid,

The first 3-dimensional laminating (3DL)

performance fibres can

carbon,polyester and

sail was constructed by Luc Dubois and

be laminated by the

other advancedyarns.

3DLand3Dr processes.

Above, from left to right,

The quantity, type and direction of fibre is adjusted to suit the

and 800 series. Left,

from left to right, 900

level of performance

series andTFi series.

INTRODUCTION

J, P. Baudet at North Sails in 1990. Since

then the process has been adopted by

replacing traditional methods of cutting, stitching and gluing.

nearly every racing boat in the Volvo Ocean RaceandAmerica'sCup-2major

application.Types of

600 series, 800 series

demanded by the

sailing grand prix.

1 Very high tooling costs ' Very high unit costs

Typical Applications

Suitability

• Sailing

• One-off and small batch production

Quality

Related Processes

Speed

• Very high strength to weight properties

• Composite laminating • Filament winding • Stitching

• Cycle time up to 5 days

Sails have a 3D 'flying shape'. In conventional sailmaking, cut patterns

TYPICAL APPLICATIONS

are stitched or glued together to produce

Although these laminating technologies

Th e thermally formed PET maintains the position ofthe fibres, which are laid

the optimum shape. In 3DL,the sails are

are currently limited to sailmaking, there

down in alignment with the direction of

molded in the optimum flying shape and so eliminate cutting and joining. This

is potential for them to be developed

stress across the sail.

tension.Therefore, this process is not

produces sails that are up to 20% lighter

for application in a variety of products such as high altitude balloons, dirigibles,

DESIGN OPPORTUNITIES

require resistance to compression.

than conventional equivalents.They are

tension structures, temporary structures

At present, opportunities for designers

The sails are not molded with a

also stronger and seamless.

and inflatable structures.

are limited because these processes are

uniform wall thickness; the thickness

restricted to sailmaking. In the future

varies with the Intended application.

The 3DL process combines the benefits

A %

performance applications. Sails are designed to be strong under

suitable for use in applications that

of composite laminating (page 206) with filament winding (page 222).The

RELATED PROCESSES

there is potential for application of these

Minimum wall thickness Is limited

The only processes capable of producing

techniques In other Industries.

by the thickness of PET film and fibre

3-dimensional sheet geometries are

very large and seamless shapes are 3DL

formed over computer-guided molds.

and 3Dr. Circular, conical, elliptical and

provide varying levels of performance

The fibre reinforcements (aramid and

similar shapes, however, can be produced

(see Images, above).The 600 series is

COMPATIBLE MATERIALS

carbon) are laid down individually along

by filament winding, composite

made up of high-modulus aramid fibres

The 2 outer films are PET coated with a

pre-determined lines of stress. They are

laminating and stitching (see upholstery,

andlaid down along the lines of stress

special adhesive.The fibre reinforcement

sandwiched between thin sheets of

page 338). Filament winding Is generally

to maintain shape and durability.The

is of carbon, aramid, polyester or a

polyethylene terephthalate (PET) coated

limited to structures no larger than

flowing shape produced In the catenary

combination ofthe 3 materials.

with a specially developed adhesive.

3 m (10 ft) in length andi m (3.3 ft) in

curves joins areas of stress with smooth,

diameter, but this is not always the case.

flowing lines of fibre reinforcement.

COSTS

The 800 and 900 series combine

Tooling costs are high. The male molds

3DLmanufacturing is along process,

and demand within the industry is very

wMwi lb

and therefore are limited to high

Specific fibre layouts and composites

reinforcement.

high.Therefore,3-dimensional rotary

QUALITY

carbon fibre with the aramid to reduce

are computer guided and adjusted to the

laminating (3Dr) was developed as a

These sails are bui'lt to perform a very

weight and stretch. Different films

flying shape of sail being made.They are

method for continuous production.

specific function. They are required to

can be used on the outside surfaces to

also very large, up to 400 m2 (4,306 ft2).

lnsteadofmanylarge3-dimens1onal

hold their shape, even in strong winds,

protect against tearing and chafing

molds, 3Dr sailmaking is carried out

be durable and lightweight and produce

and provide UV stability. Plain weave

on a single rotating drum.The shape

minimum resistance to the flow of air

polyester, known as taffeta, is used on

of the drum is manipulated as the sail

over the surface.

the outside surface ofthe TFi series to

of skill required to make reliable products

increase durability

for high performance applications.

Is constructed over it.The process is a very recent development and so is still

Aerospace vacuum and pressure

Cycle time is up to 5 days because of the lengthy curing process.

Labour costs are high due to the level

techniques are used to cure the laminates on the mold.This ensures

DESIGN CONSIDERATIONS

ENVIRONMENTAL IMPACTS

that the composite will not delaminate,

The materials and manufacturing

These sails minimize material

even when extreme loads are applied.

processes used In 3DL are expensive

consumption and reduce weight.

Three-Dimensional Laminating Process I3DLJ

Case Study

3DL sails on a TP 52 type racing boat The TP 52 type racing boat (rmage i) has here

laminate surface (image 6), or an infrared

been fitted with North Sails 3DL composite

heating system that travels above the

sails. The process starts with a bespoke sail

laminate surface (image 7), depending on the

design (flying shape), because each boat

fibre in the sail. The finished laminate is

requires a slightly different shape. There are a

Inspected after curing and left for a

range of sizes possible from 10 m2 to 500 m2

further 5 days to ensure that the adhesive

(108-5,382 ft2). The shape of the molds is

has reached its full bond strength.

computer guided, so they can be adjusted for many different sail shapes (images 2 and 3). The PET film is laid across the mold

Supply reel

Three-Dimensional Rotary Laminating Process (3Dr)

Rotating drum

Heat and vacuum pressure applied

Pneumatic rams

When the sail has fully cured, corner reinforcements, batten pockets, eyelets,

TECHNICAL DESCRIPTION

and other details are applied by sail

Each sail has an individual 3D shape. The

a computer controlled overhead gantry. It

and brought to the curing floor for a further

(image 2) and pulled tight with tensioning

makers using traditional cutting and

designer produces a CAD file, which is

operates on 6 axes, so can follow the profile

5 days to ensure the adhesive is fully cured

straps. The 6-axis computer controlled gantry

sewing techniques.

transferred onto the surface of the mold by a

of the mold exactly. The fibres follow the

and will not delaminate.

lays down the strands of carbon fibre

series of pneumatic rams. The shape of the

anticipated 'load lines'. Adhesive is applied

The 3Dr process is carried out on a

(image 4). An operator in a hang-gliding

mold will determine the 'flying shape' of the

to the fibres as they are laid down onto the

rotating drum as opposed to the static

harness inspects the sail (image 5).

sail when it is made.

mold, which helps to keep them in place.

horizontal mold used in 3DL. This enables

The PET and fibre are vacuum bagged

A PET film is laid over the mold and put

A second layer of film is laid on top of the

and held under pressure. An operator

under tension. It is coated with a specially

fibres and forced to laminate under pressure

quickly. The composite sail is formed as

then moves over the sail applying heat to

developed adhesive, designed for North

at approximately 8.6 N/cm2 (12.5 psi) from a

the drum rotates and leaves the drum

thermally form the composite over the

Sails by its industrial partners for the 3DL

vacuum bag. Heat is then applied with a

completed. The shape of the drum is

mold surface, using either a conductive

process. Strands of fibre reinforcement are

blanket to cure the adhesive. After curing,

computer controlled to produce 2-directional

heating system in contact with the

applied by a fibre placement head guided by

the composite sail is removed from the mold

curvature; the flying shape of the sail.

nuiwuiii!"''-

the sails to be put together much more

Case Study

3Dr sails on a Melges 24 A more recent development at North

Sails has been to make sails using rotary molds (sDr), which is a more rapid and cost effective process for sailmaking.The

Melges 24 racing boat is fitted with a 3Dr laminated sail (image 1). The rotating drum contains about 2000 actuators, which shape the surface into complex curvatures describing the

flying shape of a sail. The shape of the drum is manipulated to accommodate

the change in shape along the length of the sail. The drum surface is shaped to curve in 2 directions simultaneously,

using the principals of Gaussian curvature (images 2-4).

Fibre reinforcement is applied to the Featured Manufacturer

bottom PET film, which rotates on the drum (image 5). The sail leaves the drum

North Sails www.northsails.com

fully formed in 3 dimensions. Finishing touches are applied by skilled sail makers.

Featured Manufacturer

North Sails www.northsails.com

Forming Technology

Rapid Prototyping These layer building processes can be used to prototype one-offs or to direct manufacture low volume production runs from CAD data. There is no tooling involved, which not only helps to reduce cost, but also has many advantages for the designer.

INTRODUCTION Rapid prototyping is used to construct simple and complex geometries by fusing together very fine layers of powder or liquid. The process starts with

metal laser sintering (DMLS). SLA is the most widely used rapid prototyping technique and produces the finest surface finish and dimensional accuracy. These processes are utilized

a CAD model sliced into cross-sections.

mainly for design development and

Each cross-section is mapped onto the

prototyping, in order to reduce the

surface of the rapid prototyping material

time it takes to get a product to market.

Costs

Typical Applications

Suitability

by a laser, which fuses or cures the

• No tooling costs • SLS is the cheapest and DMLS the most expensive process

However, they can also be used to

• Automotive, FI and aerospace • Product development and testing • Tooling

• One-offs, prototypes and low volume production

particles together. Many materials such

direct manufacture products that have

as polymers, ceramics, wax,metals and

to be precisely reproduced with very

even paper can be formed in this way.

accurate tolerances.

Quality

Related Processes

Speed

• High definition of detail and surface finish

• CNC machining • Electrical discharge machining • Investment casting

• Long process, but turnaround is rapid because there is no tooling and data is taken directly from CAD file

This description will concentrate on 3

main processes: stereolithography (SLA), selective laser sintering (SLS) and direct

TYPICAL APPLICATIONS The high tolerances of the SLA process mean that it is ideal for producing fit-form prototypes that are used to

test products before committing to the chosen method of production.

The SLS technique is often selected to produce functional prototypes and

Electrical discharge machining (page 254) is another reductive process.

Material is removed by sparks that are generated between the tool and

Top PP mimic part with live hinges and snap fits has been produced by stereolithography.

electric seat adjustment cogs for use in the automotive industry. Above

test models because the materials

workpiece.This process is mainly used

have similar physical characteristics to

to form concave profiles that would be

Direct metal laser

This carbon strand filled nylon impellerhas been manufactured by

injection molded parts.

impractical to CNC machine.

sintering is suitable for

selective laser sintering.

DMLS is suitable for injection and

Investment casting (page 130) has

Above left

making nickel-bronze

blow molding tooling, wax injection and

many of the geometry advantages of

press tools.This process is typically used

rapid prototyping because the ceramic

in layers, contours are visible on the

to produce functional metal prototypes

molds are expendable.'

surface of acute angles. All of the parts

and low volume production runs of parts

As a result of manufacturing 3D forms

therefore require finishing when they

for the automotive, Fi, jewelry, medical

QUALITY

come out of the machine. It is possible

and nuclear industries.

SLA techniques produce the highest

to acquire a very high 'glass-like' surface

surface finish and dimensional accuracy

finish on the water clear SLA epoxy resin,

RELATED PROCESSES

of all rapid prototyping ones. All these

by polishing.

Conventional CNC machining (page 182)

layer-building processes work to fine

operations remove material, whereas

tolerances: SLS builds in o.i mm (0,004

produce intricate and precise parts (up to 77 x 61 x 230 mm/3.03 x 2.40 x 9.05 in.).

Micro modelling can be used to

rapid prototyping builds only what is

in.) layers and is accurate to ±0.15 mm

necessary. Machining produces very

(0.006 in.); SLA forms in 0.05-0.1 mm

This process builds in 25 micron (0,00098

accurate parts, but is a slow, energy

(0.002-0.004 in.) layers and is accurate

in,) layers, which are almost invisible to

intensive process. Rapid prototyping

to ±0.15 mm (0.006 in.); and DMLS builds

the naked eye and so eliminates surface

can produce complex internal shapes

in 0.02-0.06 mm (0.008-0.0024in.)

finishing operations.

by undercutting, which would be time-

layers and is accurate to ±0.05 mm

consuming and expensive to machine.

(0.002 in.).

DIRECT METAL LASER SINTERING

Selective Laser Sintering Process

Stereolithography Process

Direct Metal Laser Sintering Process

A considerable amount of heat is generated

CO2 laser

during this process because a 250 watt CO2 laser is used to sinter the metal alloy

SLA part

powders. An expendable first layer of the

Paddle to break surface tension

part is anchored to the steel plate to stop distortion caused by differing rates of

r

contraction. Such a layer also means that Solid state UV laser

the part is easier to remove from the steel

plate when the build is complete. During the sintering process, the delivery chamber

1'

rises to dispense powder in the path of

'i

the paddle, which spreads a precise layer over the build area. The build platform is incrementally lowered as each layer of Honeycomb support structure

metal alloy is sintered onto the surface of

UV sensitive liquid epoxy resin

the part. The whole process takes place in an

Build platform progresses downwards in steps of 0.05 mm to 0.1 mm (0.002-0.004 in.)

inert nitrogen atmosphere at less than 1% self-supporting = forming a nonsintered "cake-

Multiple SLS parts Build platform progresses downwards in steps of 0.1 mm (0.004 in.)

Delivery chambers progress upwards, supplying powder to the roller

oxygen to prevent oxydization of the metal powder during the build.

TECHNICAL DESCRIPTION STEREOLITHOGRAPHY

sweeps across the surface of the resin

computer-guided mirror. The build platform

All of these rapid prototyping processes

with each step downwards, to break the

progresses downwards in layer thickness

start with a CAD drawing sliced into cross-

surface tension of the liquid and control

steps. The delivery chambers alternately

confined to parts of 250 x 250 x 185 mm

at the same time and fine undercuts are

(9.84x9.84x7.28 in.).

more difficult to achieve.

polypropyl en e/polyethyl en e (PP/ PE) mimic and water clear polybutylene terephthalate (PBT)/ABS mimic. Materials

sections. Each cross-section represents a

layer thickness. The part gradually develops

rise to provide the roller with a fresh charge

layer in the build, generally between 0.05

below the surface of the liquid and is kept

of powder to spread accurately over the

mm and 0.1 mm (0.002-0.004 in.) thick for

off the build platform by a support structure.

surface of the build area. Non-sintered

its m ech ani cal properti es - stran d fill ed

COMPATIBLE MATERIALS

that can withstandtemperatures up to

SLA modelling. The model is built 1 layer

This is made in the same incremental way,

powder forms a 'cake', which encapsulates

materials having better strength in

The SLS process is compatible with a

2000C (3920F) have been developed for

at a time by an UV laser beam directed by a

prior to building the first layer of the part.

and supports the model as the build

certain geometries.The orientation of

variety of nylon-based powders. The

the SLA process,

progresses. The whole process takes place

SLS parts in regular nylon powders has

tough Nylon 11 is heat resistant up to

„ The DMLS process is compatible

with specially developed metal alloys: 2 examples are nickel-bronze, which is

computer-guided mirror onto the surface of

The orientation of the part can affect

the UV sensitive liquid epoxy resin. The UV

SELECTIVE LASER SINTERING

in an inert nitrogen atmosphere at less than

to be considered, to maintain accuracy.

1500C (3020F) and so can be used to

light precisely solidifies the resin it touches.

In this layer-additive manufacturing

1 % oxygen to stop the nylon oxydizing when

For example, a tube is built vertically to

produce functional prototypes that are

Each layer is applied by submersion of the

process, a CO2 laser fuses fine nylon powder

heated by the laser beam.

keep it round; if built horizontally the

suitable for working situations. Carbon

slightly harder wearing than aluminium

build platform into the resin. The paddle

in 0.1 mm (0.004 in.) layers, directed by a

tube would be very slightly oval. A large

filled and glass filled materials have been

tooling, and steel alloy, which has similar

flat plane should be manufactured at an

developed to build structural parts. The

characteristics to mild steel,

incline because if it is built flat there will

carbon filled material Windform™ XT

DESIGN OPPORTUNITIES

The SLS technique forms parts with physical characteristics similartothat

advantage of DMLS is that it produces

be too much stress in the part, which will

was designed specifically for use in wind

COSTS

There are many advantages to using

very accurate parts (±0,05 mm/0.002

result in warpage.

tunnels. It has good resistance to wind

There are no tooling costs.

rapid prototyping technology such as

of injection molded polymers. Because

in.) with fine surface definition

load and vibration, superior mechanical

reducing time to market and lowering

parts can be made with live hinges

(0.02 mm/0.0008 in.layers),andthe

product development costs. However,

and snap fits, this process is ideal for

final product is 98% dense metal. As a

the most desirable qualities of this

functional prototypes.

process for designers are not cost savings, they are that complex, intricate

The SLA technique is suitable for water clear, translucent and opaque parts.

properties and high surface finish, which

The cost of rapid prototyping is largely dependent on build time. Cycle

makes this an ideal material for Fi and

time is slow, but these processes reduce

result, DMLS parts have good mechanical

that the hinge is on the horizontal plane, for strength; if it was built vertically the layers would be too short to withstand

aerospace applications. Recent material

the need for any preparation or further

strength and so are suitable for tooling

the stress of opening and closing, and

developments for the SLS process include

processing and so turnaround is very

and functional metal prototypes.

wouldfail.

powders with rubber-like qualities and

rapid. Individual part cost is reduced if

In the SLS system, multiple parts can be built simultaneously and on different

those with integral colour, to reduce post¬

multiple products are manufactured

DESIGN CONSIDERATIONS

processing operations.

simultaneously,The SLS powders are

A live hinge is always constructed so

and previously impossible geometries

The surface finish can be improved with

can be built with these processes to

polishing and painting, SLA materials

fine tolerances and precise dimensions.

mimic conventional thermoplastics,

The main restriction for these processes

planes because the non-sintered powder

There is no tooling and so changes to the

which means SLA is good for making

is the size of the machine: SLS is limited

supports the sintered parts. By contrast,

resin polymers that are categorized

of components can be built around and

design cost nothing to implement.The

parts with the visual and physical

to parts of 350 x 380 x 700 mm (13.78 x

parts made by SLA and DMLS processes

by the thermoplastics that they are

inside one another to reduce cost.

combination of these qualities provides

characteristics of the final product.

14.96 x 27.56 in.); SLAis restricted to parts

need to be supported and undercuts

designed to mimic. Some typical

ofsoox 500x500 mm (19.69x19.69

must be tied into the build platform.This

materials include acrylonitirile

choice of process and layer thickness:

x 19.69 in.); while the DMLS process is

means that fewer parts can be formed

butadiene styrene (ABS) mimic.

typically SLS machines build 2 mm to

limitless scope for design exploration and opportunity.

DMLS provides an alternative to machining aluminium parts.The

The SLA process uses liquid epoxy

self-supporting and so large numbers

The build times are affected by the

Case Study

Building an SLA part of PE mimic The rapid prototyping machine works

tank to break the viscous surface tension

and any other contamination (image 9) and

automatically, overnight. The CAD data from

and ensure that the correct depth of layer is

the parts are then fully cured under intensive

a .stl file guides the UV laser (image ij.The

in place to be fused (image 5). The finished

UV light for 1 minute (image 10). The build

SLA parts appear as ghost-like forms in the

parts are left to drain and then removed

strata are Just visible in the finished part

clear epoxy resin (image 2). Each pass of

from the build tank along with any uncured

(image 11) and can be removed with abrasive

the laser fuses another 0.05 mm to 0.1 mm

epoxy resin residue (image 6). The parts are

blasting,polishing or painting.

(0.002-0.004 in.) to the preceding layer by

separated from the build platform (image

constructing the 'skin' (image 3) and then

7) and the support structure that separated

filling in the'core'material (image 4).The

them is carefully detached (image 8). An

build platform moves down 1 step, and the

alcohol-based chemical (isopropinol alcohol)

paddle sweeps across the top of the build

is used to clean off the uncured resin liquid

3 mm (0.079-0.118 in.) per hour in o.i mm (0.004 m) layers; SLA machines build 1.2 mm to 12 mm (0.047-0.47 in.) per hour;

and DMLS machines build at a rate of 2-12 mm3 (0.00012-0.00073 in*3) Per

hour. One drawback with SLS is that parts | have to be left to cool, which can increase

cycle time by up to 50%. Labour costs are moderate, although

they depend on finishing required. SLS parts are generally less expensive than SLA ones because they needless post-

building processing. DMLS parts are typically cut from the steel plate by EDM wire cutting and are then polished. This can be a 1 en gthy process, but it depen ds 4

'V

on the product and application.

ENVIRONMENTAL IMPACTS

f ¦

All the scrap material created during rapid prototyping can be recycled, except the carbon filled powders.These processes are an efficient use of energy and material, as they direct thermal

energy to the precise point where it is required.

Featured Manufacturer

CRDM www.crdm.co.uk

5

IP

V'

Case Study

Building an SLS part The SLS process takes place in a sealed, nitrogen rich atmosphere that contains less than 1% oxygen. The temperature

inside the building chamber is maintained at i700C (338^), Just below the melting point of the polymer powder, so that as soon as the laser makes

contact with the surface particles they are instantly fused (image i) by the i20C (220F) rise in temperature. Following the sintering process the delivery chamber moves up to deliver powder to the roller, which spreads it across the surface of the build area (image 2), coating the part with an even layer of powder (image 3). The building process can take anything from 1 hour to 24 hours. Once

it is complete, the build platform is raised (image 4), pushing the mixture of non-sintered powder and sintered parts

is disposed of in aThe clean-up I intoofapowder clear acrylic container. block booth and work begins to excavate the parts (image 5). The non-sintered'cake'

encapsulates the parts and has to be carefully brushed away so that individual parts can be removed for cleaning (image 6). Once most of the excess powder has

been removed (image 7), the parts are blasted with a fine abrasive powder (image 8).The final partis an exact replica of the computer model, accurate

to 150 microns (0.0059 in.) (image g).

Featured Manufacturer

CRDM www.crdm.co.uk

Building a DMLS part The DMLS process builds a metal part from

A steel build plate is set precisely inside

data within a .stl file. To make the process

the build chamber (image 2). Its thickness is

more efficient, each layer of the build is not completely filled in by the laser, The part is broken up into 3 main elements, which are

is guided across the surface layer by a CNC

This part will be used as an insert in

mirror (image 5). After each pass of the laser,

an injection molding tool. Some 20,000-

13-45 mm (0.51-0.77 in.), depending on the

a new layer of powder is spread over the build

30,000 components can be produced

depth of part to be built on it.

area (image 6).

with the part before any significant wear

The fine metal powder used to form this

Once building is complete, the build

occurs. Harder metal alloy powders will

the outer skin, the inner skin and the core. For

part comprises spheres of nickel-bronze alloy,

platform is raised (image 7), the excess

produce 100,000-200,000 parts from a

every 3 layers of metal powder that are spread

20 microns (0.00078 in.) in diameter.The

powder is brushed away (image 8) and

single impression tool.

the outer skin is sintered 3 times, the inner

powder is sieved into the delivery chamber

the steel plate removed with the part still

skin is sintered twice and the core is sintered

and then spread evenly across the build area

attached (image 9). The part is eventually

only once. A cross-section of atypical DMLS

in preparation for the first pass of the laser

removed from the steel build plate by

part shows the outer skin, inner skin and core,

(image 3). When the build area is ready for

EDM wire cutting (see electrical discharge

visible in the different tones (image 1).

sintering to begin (image 4), the CO2 laser

machining, page 254).

Featured Manufacturer

CRDM www.crdm.co.uk

Cutting Technology

TECHNICAL DESCRIPTION

Photo Etching Process

In stage 1, the metal workpiece Is carefully prepared, because it Is essential that It is clean and grease free to ensure good adhesion between

Cutting Technology

the film and the metal surface. The

Photochemical Machining

photosensitive polymer film Is applied by hot roll laminating or dip coating (page 68). In this case it Is being hot

Unprotected metal is chemically dissolved in photochemical machining. Masks are designed so that components are cut out and engraved simultaneously. The results are both decorative

roll laminated onto the metal. The

INTRODUCTION

coating Is applied to both sides of the

This chemical cutting process, which is

workpiece because every surface will

used predominantly to mill and machine

be exposed to the chemical machining

thin sheet metals, is also known as

process.

chemical blanking and photofabrication. and functional.

1 Very low tooling cost 1 Moderate to high unit costs

Stage 1: Applying photosensitive resist film

In stage 2, acetate negatives (the UV light source

Decorative chemical cutting is known as

photo etching (page 392). Photochemical machining has 3 main

are printed from CAD or graphics applied to either side of the workpiece,

Typical Applications

Suitability

functions: weight reduction, scoring

• Aerospace • Automotive • Electronics

• Prototype to mass production

and cutting out (known as profiling). It

software files. The negatives are Unexposed areas remain soft

Acetate negative

Exposed film hardens

can chemically remove surface material,

Related Processes

Speed

• High: accurate to within 10% of material thickness

• Abrasive blasting • CNC machining and CNC engraving • Laser cutting

• Moderate cycle time (50-100 microns/ 0.002-0.00/i in. per hour)

different on each side, so where they

cutting action is precise to within 10% of material thickness and so is suitable

do not meet up, the cut will only go

1} 1} ^

fortechnical application. Profiling is achieved by attacking the material from

half way through the sheet. The soft and unexposed photosensitive resist

film Is chemically developed away. This

both sides simultaneously.Therefore, this

process exposes the areas of the metal

Stage 2: UV exposure

process is limited to foils and thin sheet

that are to be etched.

metal between 0.1 mm and 1 mm (0.004-

In stage 3, the metal sheet is

0.04 in.) thick. However, accuracy can be Oscillating nozzles

maintained only in sheet materials up to 0.7 mm (0.028 in.) thick.

TYPICAL APPLICATIONS The technical aspects of this technology are utilized in the aerospace, automotive

Metal dissolves . in acid

-1 x 1 irr

Exposed film protects metal surface

the plastic (typically polycarbonate)

passed under a series of oscillating nozzles that apply the chemical etch. The oscillation ensures that plenty of oxygen is mixed with the acid to accelerate the process. Finally, the

protective polymer film is removed

Ferric chloride etchant

XXX X-

and electronics industries.

Circuit boards are made by coating

then both sides of the combined workpiece - resist film and negative - are exposed to UV. The patterns are

andean mark lines on most metals. The Quality

tool) are prepared in advance and

from the metalwork in a caustic soda mix to reveal the finished etching.

L Stage 3: Chemical cutting

board with a thin layer of copper. Areas of the metal are then chemically removed in order to create the positive image of the circuit board.

Other products include modelmaking nets, control panels, grills, grids, meshes, electronic parts, micro metal components and jewelry.

lillfe I

RELATED PROCESSES Laser cutting (page 248) and engraving

which can cause distortion in very thin

QUALITY

metal structure. The surface finish is

matt, but can be polished (page 376).

metals. Lasers are typically suitable for

This process produces an edge finish free

thicker materials, which are impractical

from burrs, and it is accurate to within

for photochemical machining.

10% of the material thickness. Another

DESIGN OPPORTUNITIES

advantage of photochemical machining

Photochemical machining is used to

engraving (page 396) also produce a heat-affected zone (HAZ), which can

is that there is no heat, pressure or tool

score lines, mill holes, remove surface

contact, and so the process is less likely

result in distortion in the workpiece.

to cause distortion, and the final shape is

material and profile entire parts (blanking).These different functions

CNC machining (page 182) and CNC

Photochemical machined engravings

are used to produce similar products.

have the same finish as an abrasive

However, lasers heat up the workpiece.

blasted surface (page 388).

free from manufacturing stresses. The chemical process does not affect

the ductility, hardness or grain of the

are applied simultaneously during machining.The type of cut is determined by the design of the protective mask.

Case Study

1

--*

Photochemical machining a brass screen The design for the negatives is prepared

brass sheet is degreased in a bath of 10%

using graphics software (image i )„ which

hydrochloric add. It is washed and dried, and

(image 7), the process is repeated until the

shows how the chemical machining process

a photosensitive film is laminated onto both

chemical has etched through the entire

works-The left hand drawing is the reverse

sides (image 3). The process takes place in a

thickness of material (image 8). This can take

and the right hand drawing is the front

dark room, to protect the film.

up to 25 minutes for 0.7 mm (0.028 in.) brass.

of the workpiece.The 2 sides are etched

The coated workpiece is placed into an acrylic jig (image 4). The negatives are aligned

out on both sides will be cut through

and mounted onto each side of the jig. The

the brass sheet and the tabs that connected

(profiled). Areas that are black only on 1 side

assembly is placed under a vacuum and

the workpiece are trimmed (image gi

will behalf etched.

exposed to UV light on both sides (image 5),

The negatives are printed onto acetate

t

mI

Ferrous metals will take longer.

simultaneously, so the areas that are blacked

(image 2).Then a 0.7 mm (0.028 in.)

.y

Afterthe first stage of chemical machining

Finally, the brass screen is removed from

1 ^iMi

I

Unexposed photosensitive film is washed off

I

in a developing process (image 6)

g

s 78,v (CMYK/Pieviewl

that is, by the photosensitive polymer resist film. Score lines can be machined to act as

foldlines.Changing the width of score will determine the angle of fold, and this

a.T. \.u,

w*** 1 • * • * ***

0*3. X-uJ. _i

is particularly useful for modelmaking and other secondary operations.

Profiling entire parts is achieved by chemically cutting the sheet from

> o X

X S** I • Ar-C* I** * J ^

rv *•*'* " • 7. A

Hi

*•¦

mate aa ÿ;

I a"-

both sides. Lines that do not match up on both sides will become surface

li, i, J TF

markings on 1 side.Therefore, sheets can

S zi W- J-l

be profiled and decorated (or scored) in a -fidop. e|.g> •Sgjopt

single operation.

Photochemical machining is suitable for prototyping and high volume production.Tooling costs are minimal:

the negatives can be produced directly from CAD drawings or artwork and will last for many thousands of cycles.

radii, holes, slots and bars is 1.5 times the thickness of the material.

Although any thickness of sheet

operations such as electroplating (page 364) andforflat sheet packaging.The

aluminium, copper, brass, nickel,tin and

Labour costs are moderate and

silver. Of these, aluminium is the easiest,

depend on the complexity and duration

shape of the tabs -V-shape or parallel - is

and stainless steel is the hardest and so

of photochemical machining process.

takes longer to etch.

This means that small changes are

material can be photo etched, only sheets

determined by the secondary operations.

inexpensive and adjustments can

and foils between 0.1 mm and 1 mm

A V-shape tab is for manually breaking

be made to the design. For these

(0.004-0.04 in.) can be profiled using

out, whereas a parallel tab is for parts

Glass, mirror, porcelain and ceramic

ENVIRONMENTAL IMPACTS

are also suitable for photo etching,

During operation, metal that is removed

reasons this process is suitable for

photochemical machining. Materials

that are punched or machined. V-shaped

although different types of photo resist

from the workpiece is dissolved in the

experimentation during design.

more than 1 mm (0.04 in.) thick will have

tabs can be sunk within the profile of the

and etching chemical are required.

chemical etchant. However, offcuts and

a visible concave or convex edge profile

part so that when removed there is no burr. The tabs can be half the material

COSTS

very few rejects because photochemical

thickness and a minimum of 0.15 mm

The only tooling required is a negative that can be printed directly from CAD

machining is a slow, controllable process.

DESIGN CONSIDERATIONS The intricacy of a pattern is restricted by the thickness of the material: any

left by the chemical process. Tabs are an essential part of the

other waste can be recycled. There are

The chemical used to etch the metal is

design for profiling. They connect the parts to the workpiece and hold the

(0.006 in.) each.

as the smallest details are larger than

parts in place as they are being cut out.

COMPATIBLE MATERIALS

the material thickness.The minimum

Tabs make handling easy, especially if

Most metals can be photo etched

multiple parts on the same sheet reduces

Both of these chemicals are harmful, and

dimension for internal and external

the parts are very small or in secondary

including stainless steel, mild steel.

cycle time considerably.

operators must wear protective clothing.

configuration can be machined, as long

data or a graphics software file. Cycle time is moderate. Processing

one-third ferric chloride. Caustic soda is

Featured Manufacturer

needed to remove spent protective film. Mercury Engraving www.mengr.com

Laser Cutting Process technical description

I I «

Mirror

CO, and Nd:YAG laser beams are guided

.

to the cutting nozzle by a series of fixed mirrors. Due to their shorter wavelength,

i

Cutting Technology

Laser Cutting

Nd;YAG laser beams can also be guided to the cutting nozzle with flexible fibre optic cores. This means that they can cut along 5 axes because the head is free to rotate in any direction. The laser beam is focused through a lens

This is a high precision CNC process that can be used to cut, etch,

that concentrates the beam to a fine spot,

engrave and mark a variety of sheet materials including metal,

between 0.1 mm and 1 mm (0.000^-0.00^ in).

The height of the lens can be adjusted

plastic, wood, textiles, glass, ceramic and leather.

to focus the laser on the surface of the material. The high concentration beam melts or vaporizes the material on contact. The

pressurized assist gas that blows along the path of the laser beam removes the cutting Typical Applications

Suitability

• Consumer electronics • Furniture • Model making

• One-offs to high volume

Quality

Related Processes

Speed

• High quality finish • Precision process

• CNC machining and engraving • Punching and blanking • Water jet cutting

• Rapid cycle time

1 No tooling costs 1 Medium to high unit cost

debris from the kerf.

Vacuum bed

INTRODUCTION

blanking (page 260) can all be used to

without reducing strength or distorting

The 2 main types of laser used for this

produce the same effect in certain

the part. Therefore very thin and delicate

thin sheet materials down to 0.2 mm

(PA),polyoxymethylene (POM) and polystyrene (PS). Of the metals, steels

process are CO2 and Nd:YAG. Both work

materials. However, the benefit of the

materials can be cut in this way.

(0.0079 i11-); it15 possible to cut sheets up

cut betterthan aluminium and copper

to 40 mm (1.57 in.), but thicker materials

alloys, for example, because they are not

greatly reduce processing speed.

as reflective to light and thermal energy.

by focusing thermal energy on a spot

laser cutting process is that it cuts

0.1 mm toi mm (0.0004-0.004in.) wide

thermoplastics so weill that they require

Raster-engraving methods can be used to produce logos, pictures and fonts

This process is ideally suited to cutting

to melt or vaporize the material. Both

no finishing; the cutting process leaves a

on the surface of materials with cuts of

Different laser powers are required for

operate at very high speeds to precise

polished edge. Laser cutting can also be

various depths. Certain systems are very

different operations. For example, lower

COSTS

tolerances and produce accurate parts

used to score and engrave, so competes

flexible and can be used to engrave from

powered lasers (150 watts) are more

There are no tooling costs for this

with very high edge finish. The main difference between them is that CO2

with CNC engraving (page 396), abrasive blasting (page 388) and photo etching

a variety of file formats.

suitable for cutting plastics because they

process. Data is transmitted directly from

leave a polished edge. High-powered

a CAD file to the laser cutting machine.

lasers produce a 10 micron (0.00039 in-)

(page 392) for some applications.

DESIGN CONSIDERATIONS

lasers (1 to 2 kilowatts) are required to

These are vector-based cutting systems:

cut metals, especially reflective and

m ateri al thi ckn ess. Thi cker m ateri al s take

QUALITY

the lasers follow a series of lines from

conductive alloys.

considerably longer to cut. However, suitable CAD files must be

infrared wavelength and Nd:YAG lasers produce a more versatile 1 micron

Cycle time is rapid but dependent on

The choice of material will determine

point to point.The files used are taken

the quality of the cut. Certain materials,

directlyfrom CAD data, which is divided

COMPATIBLE MATERIALS

TYPICAL APPLICATIONS

like thermoplastics, have a very high

generatedforthe laser cutting machine,

surface finish when cut in this way.

multitude of materials including timber,

which may increase initial costs.

modelmaking, furniture, consumer

Laser processes produce perpendicular,

up into layers that determine the depth of each cut. It is important that all lines are 'pedited' (joined together) so that the

These processes can be used to cut a

Applications are diverse and include electronics, fashion, signs and trophies,

smooth, clean and cuts with a narrow

laser cuts on a continuous path. Replica

marble,flexible magnets, textiles and

point of sale, film and television sets, and

kerf in most materials.

lines also cause problems because the

fleeces, rubber and certain glasses

Careful planning will ensure minimal

laser will treat each line as another cut

and ceramics. Compatible plastics

waste, but it is impossible to avoid

and so increase process time.

Thermoplastic scrap, paper and metal

(0.000039 It1-) infrared wavelength.

exhibition pieces.

DESIGN OPPORTUNITIES

The process requires very little labour.

RELATED PROCESSES

These processes do not stress the

CNC machining (page 182), water jet

workpiece, like blade cutting, so small

an d. DWG. Any oth er fil e form ats m ay

include polypropylene (PP), poly methyl methacrylate (PMMA), polycarbonate (PC), polyethylene terephthalate

cutting (page 272) and punching and

and intricate details can be produced

need to be converted.

glycol (PETG), carbon fibre, polyamide

Compatible file formats include .DXF

Above

veneers, paper and card, synthetic

ENVIRONMENTAL IMPACTS

offcuts that are not suitable for reuse.

can be recycled,but not directly.

Laser cutting produces a polished edge on certain thermoplastics and so eliminates finishing operations.

:ase Study

Laser cutting, raster engraving and scoring LASER CUTTING PLASTIC

LASER RASTER ENGRAVING

The pattern was designed by Ansel Thompson

Adjusting the strength and depth of the laser

In this case the laser is being used at only

for Vexed Generation in 2005. This series

cutter can produce interesting finishes. Raster

3% of its potential. Scoring produces 'edge glow' effect in the cut detail (image 4) I his

LASER SCORING

of samples demonstrate the versatility of

engraving uses only a small percentage of

the laser cutting process. The strength and

the laser's power and produces engravings

is caused by light picked up on the surface of

depth of the CO2 laser can be controlled to

up to 40 microns (0.0016 in.) deep (image 3).

the material being transmitted out through

produce a variety of finishes.The laser is used

This form of engraving can be carried out

the edges. The scoring acts like an edge and so

to cut translucent 3 mm {o.n8 in.) thick poly

on a variety of materials and surfaces. For

lights up in the same way.

methyl methacrylate (PMMA) (image i).This

example, anodized aluminium maybe raster

is a relatively thin material, so the laser can

engraved to reveal the bare aluminium

LASER CUTTING WOOD

work rapid ly even though it is a complex and

beneath, instead of being printed. The sample

In this example 1 mm (0.04 in.) thick birch

intricate profile. The result (image 2) took only

took approximately 25 minutes to complete,

plywood is being cut and scored to form

12 minutes to complete.The laser leaves a

which is considerably longer than for a simple

part of an architectural model. The first pass

polished edge on PMMA materials and so no

cutting operation.

scores surface details laid out in the top

finishing operations are required.

More powerful lasers can engrave deeper channels in materials. However, when the

layer of the CAD file. Secondly, the laser cuts internal shapes and finally the outside profile

depth exceeds the width, problems with

(image 5). The entire cutting and scoring

material removal result in a poor quality

process takes only 8 minutes. The parts are

finish on the cut edge.

removed and assembled to form a building facade in relief (image 6).

Case Study

Laser cutting the Queen Titania Alberto Meda and Paolo Rizzatto designed the

(image 4). The parts on this sheet do not

The assembled structure is anodized (page

Queen Titania for Luceplan in 2005 (Image 1),

necessarily make up an entire light. Many

360) before the electronic and lighting

It is a modified (1.4 m/4.6 ft long) version of

lights are made in each batch, and so the

components are added. The reason for

the Titania, which was first manufactured by

parts are nested to optimize production and

anodizing is to ensure longevity of the

Luceplan in 1989.

reduce waste.

finish of the light. The surface of untreated

The cut parts do not have to be de-burred

aluminium Is less stable and more likely to

of an aeroplane wing.The parts are laser cut

or treated in any other way, which Is a major

change over time.The surface finish is grey,

from a sheet of aluminium and assembled to

advantage of laser cutting. Each part is

and light filters produce the vibrant colours.

The structure of the light is reminiscent

form a lightweight and rigid structure. The process starts by loading a sheet of aluminium into the laser-cutting machine (image 2). This is an Nd:YAG and oxygen cutting process operating at 5oo watts.

The machine is capable of cutting sheet steel up to 25 mm (0.98 in.) thick and aluminium up to 5 mm (0.2 in.) thick (image 3). Aluminium produces a larger HAZ (heat-affected zone) and so is trickier to laser cut.

The laser cutting process is rapid: each sheet takes only 8 minutes to process

removed from the sheet and hung up ready for assembly (images 5 and 6). The light is assembled in 2 halves, which are joined by riveting (images 7 and 8).

' Cutting Technology

Electrical Discharge Machining High voltage sparks erode the surface of the workpiece or cut a profile by vaporizing the material, making this a precise method of machining metals. Material is removed from the workpiece and a texture is applied simultaneously.

INTRODUCTION

and die-sink complex geometries deep

Electrical discharge machining (EDM)

into metal parts. Wire EDM is similar in

has revolutionized toolmaking and metal

principle to hot wire cutting polymer

prototyping. It is extremely precise and

foams and is used to create internal and

can be used to texture metal surfaces as

external profiles with either parallel

well as machine them.This makes it ideal

ortapering sides. Combined, these

for toolmaking for injection molding

processes provide metalworkers with

(page 50) and other plastic forming

unlimited versatility.

Costs

Typical Applications

Suitability

processes, which is the largest area of

• Low tooling costs for EDM; no tooling costs for wire EDM; very high equipment costs • Moderate to high unit costs

• Precision metalwork in the aerospace and electronics industries • Tool making

• One-offs and modifications to existing metalwork • Low volume production

application for this process.

Quality ¦ • Very high control of surface finish and

r

Related Processes

Speed

• CNC machining • Laser cutting • Water jet cutting

• Long cycle time

TYPICAL APPLICATIONS

There are 2 versions of the EDM

EDM equipment is very expensive, so

process: die sink EDM (also known as

its use is limited to applications that

spark erosion) and wire EDM (also known

demand the very high levels of precision and the ability to work hardened steels

as wire erosion). Die sink EDM can be used to bore holes, texture surfaces

and other metals that are impractical

for CNC machining (page 182). It has been widely adopted by the toolmaking 1 n dustry for i n j ecti on m ol din g, m etal

Alternatives to wire EDM include

casting and forging. It is also used for

water jet cutting (page 272), laser

modelmaking, prototyping and low

cutting (page 248) and the power beam processes (page 288) for certain profiling and drilling procedures. All of these

volume production of typically no more than 10 parts.

processes have high equipment costs,

RELATED PROCESSES

so the choice is often determined by available facilities. Wire EDM is suitable

EDM is generally used in conjunction with CNC machining.The electrodes

for parts up to 200 mm (7.87 in.) thick

Top On these die sfnlc EDM tools, the patination of black vaporized metal shows the cutting area.

Above right This very small die sink EDM tool was cut out using the wire EDM process. It is too small and intricate to

Above left The VDI scale is used to

produce by conventional machining.

measure the texture of the surface.

The quality of the finish and resulting

(tools) for die sink EDM are machined by

that require high dimensional accuracy,

conventional metalworking techniques

parallel kerf walls and a controlled

speed and voltage. High voltage and high

(see image, top). However, complex

surface texture.

cutting speed produce a rough texture.

using wire EDM, which combines the

QUALITY

and more passes produce finer surface

2 processes (see image, above right).

The quality of EDM parts is so high they

textures. Parts can be manufactured

can be used to manufacture tooling for

accurate to 5 microns (0.00019 in-)-

and intricate tools are sometimes cut

Die sink EDM has replaced CNC

texture are determined by the cutting

Lower voltage, slower cutting speeds

machining in applications that require

injection molding without any finishing

accurate and intricate internal features.

operations. Surface finish is measured

DESIGN OPPORTUNITIES

EDM is used because it can produce

on the Association of German Engineers'

A major advantage for designers is the

geometries that are not feasible with

VDI scale (see image, above left).The

ability of this process to cut metals and

any other process. Internal features,

VDI scale is comparable with roughness

apply a texture simultaneously.Textures,

especially in hard metals, are not

average (Ra) 0.32-18 microns (0.000013-

including matt and gloss, are usually

practical for CNC machining because

0.00071 in.). Many of the plastic products

applied after machining operations

they would require very fine cutting tools,

surrounding us today have been molded

using abrasive blasting or photo etching

which would wear out rapidly.

in tools shaped and finished by E DM.

techniques. EDM produces accurate

TECHNICAL DESCRIPTION

Die sink EDM Process

D

Die sink EDM takes place with the

Case Study

electrode (tool) and workpiece

Die sink EDM

submerged in light oil, similar to paraffin. This fluid is continuously

Movement in x, y and z axes

running and so both maintains the temperature of the workpiece and

Copper electrode

(tool)

dielectric, which insulates the working area and sustains the static discharge

The copper electrode (tool) and metal

¦=>

proximity, which initiates the spark Dielectric fluid in continuously running bath

erosion process. High voltage sparks Spark erosion

leap from the electrode to the workpiece

Workpiece

and vaporize the surface of the metal.

Clamp (+]

The electrical discharges jump between the closest points on the electrode and

even surface material removal. There is no pressure required in operation. The electrode is lowered into the workpiece very gradually,- the speed of the process is dependent on

the finish required and can range from 2 mm3 (0.00012 in.3) per minute to over 400 mm3 (0.024 in.3) per minute for very

rough finishes. As the tool is sunk into the workpiece it is continuously agitated

(image 7), This is a very shallow impression;

was once used as the insulating fluid, until

cavity directly into the surface of high-carbon

this oil was developed.

deep cavities.

Sparks and fumes are given off during

complex and intricate cavities into hard

rough cutting (image 4). The copper electrode

metals like this, other than by using EDM.

is charged with an electric current, which

The copper alloy electrode (tool) is inserted

when they come into very close proximity.

the computer guided tool head (image 2).

There are several thousand sparks per

The EDM machines are programmed to the

second. Each spark vaporizes a small piece

settings required forthe tool.The black areas

of surface material. The arcs will jump

show the parts of the tool that have been

across the shortest distance between the

exposed to spark erosion. Each tool may last

electrode and workpiece, which ensures

for only 5 uses before it has to be replaced.

evenly distributed surface removal. In this

radius is also affected by the thickness

If extreme levels of precision, to within

case the process is vaporizing around 400

the workpiece, creating sharp corners

of the wire electrode, which is typically

5 microns (o.oooig in.), are required, new

mm3 (0.024 in.3) per minute. The resulting

and complex features that would

50 microns (0.0020 in.) to 300 microns

tools are machined for each EDM operation.

surface finish is very rough (image 5).

otherwise be impractical.The erosion of

(0.012 in.) in diameter.

The thickness of material that can be cut by wire EDM ranges from o.i mm

(0.1%), so small internal radii and

(0.004 in.) up to 200 mm (7-87 i^-).

flushes vaporized material away from

Wire EDM can be used in much the same way as hot wire cutting polymer

foam, although it is considerably more precise andmuch slower,The equipment

(black powder) can be flushed away, so maximum depth is affected by the depth

requires a high level of skill to operate.

to diameter ratio. Very deep profiles are

Stress is not applied to the electrode

machine settings, eliminating the need

(tool or wire) or workpiece during

for further finishing operations.

processing because the metal is not

o > r~ o

cs

possible, but may require extra flushing, which will increase cycle time.

COMPATIBLE MATERIALS

produce geometries that are not possible

being shaped by force, but in stead by high voltage sparks that vaporize the

Many metals can be shaped by EDM

with conventional machining. For

surface. Other than the obvious, this

techniques.The hardness of the material

instance, the guide heads on many wire

has many processing advantages. For

does not affect whether it can be

EDM machines can move independently

example, multiple thin-walled parts can

processed in this way. Metals including

during the cutting process.The

be stacked up and cut by wire EDM to

stainless steel, tool steel, aluminium,

advantage is that complex tapers, up to

reduce processing time.

titanium, brass and copper are

30°, can be cut with extreme precision,

m o

jumps to the oppositely charged workpiece

into a tool holder that is registered with

negative electrode (tool) is reproduced in

slower than the erosion of the workpiece

(0,003 in.3) per minute (image 6), This produces a much finer surface texture die sink EDM can also be used to form very

applications.The minimum internal

the copper electrode (tool) is considerably

much slower, in this case as low as 50 mm3

similar to paraffin (image 3). In fact, paraffin

that are not suitable for cavities.The

the cutting area and ensures even and

commonly shaped in this way.

which is not possible with any other

DESIGN CONSIDERATIONS

machining technique.

Although these processes can produce

COSTS

internal radii as small as 30 microns

Wire EDM does not require tooling.

Die sink EDM can be used to produce

emboss surface textures and graphics. In this

The second stage of machining is

case study, Hymid Multi-Shot are forming a

larger than 500 microns (0.02 in.) in most

but depends on the capabilities of

These processes can be used to

submerged in a dielectric fluid, which is

electrode can be machined into shapes

the equipment.The depth that can be produced by die sink EDM is limited by the ease with which vaporized metal

textures, which are determined by the

tools. It can also be used to bore holes or

However, these do not need to be any

complex features are reproduced to the

efficient material removal.

The tool and workpiece are inserted and

This is because a negative copper

same precision as simple geometries.

and descends in a spiral. This action

separate tool for finishing.

steel (image 1). It is not practical to machine

workpiece are brought within close

the workpiece, forming continuous and

including a tool for roughing out and a

well as machining entire cavities for injection molding, it is often used to modify existing

flushes out vaporized material. It Is also

within In It.

This process is widely used for tool-making. As

Featured Manufacturer

internal geometries on parts that are not

(0.0012 in.), it is always better to use

However, it does consume wire electrode

Hymid Multi-Shot

possible with conventional machining.

larger radii to avoid stress concentration.

continuously, which must be replaced.

www,hymid,co,uk

CD

o X >

O > O

in

TECHNICAL DESCRIPTION

Wire EDM Process

Case Study

In this process the wire electrode, which is usually copper or brass, is fed

Wire EDM

between the supply spool and take up Supply spool!-)

spool. It is charged with a high voltage, which discharges as the wire progresses

through the workpiece. Similar to die sink EDM, the spark occurs in the smallest gap between the metals. There are many thousand sparks per second, which vaporize very small amounts of the metal surfaces. The wire electrode

Unlike die sink EDM, which is used to form

workpiece and wire electrode are submerged

where the wire has cut from the pre-drilled

internal relief cavities, wire EDM is used to cut

in deionized water, which acts as an insulator

hole to the cutting profile (image 7): on the

internal and external profiles. The wire is held

(image 3). Once submerged, the cutting

left are the parts prior to cutting, in the centre

under tension to cut straight lines. The guide

process begins (image 4). It is a long process;

is the finished workpiece and on the right the

heads move in tandem along x and y axes to

in this case the 36 mm (1.42 in.) workpiece is

material that has been removed.

produce profiles and independently along x

cut at 1.5 mm (0.059 in.) per minute. This will

andy axes to produce tapers. The wire acts

produce the desired finish.

like the copper tool used in die sink EDM and

is not recycled; instead it is replaced

is usually a copper alloy.

continuously, which maintains the

There are many cutting operations in

accuracy of the process.

This process is submerged in deionized water, which is maintained at

measured on a micrometer (image 6). On the

illustrates one of those operations, the

finished article you can just make out the kerf

other wire EDM operations.The partly

running to flush spent material and

Clamps 1+)

recycled through a filtration system. Static wire guide

The upper wire guide can be moved

Take-up spool (-)

machined high-carbon steel workpiece (image 1) is loaded into a jig and clamped in place. A small hole is drilled in

along x and y axes to enable cutting

preparation, which the wire electrode is

angles up to 30°.

automatically fed through (image 2). The guide heads are brought close to the workpiece for precision and both the

Die sink EDM tools are typically made

(0.012- 0.024 in.3) per minute. As the

from a copper alloy, which can be shaped

term suggests, this will produce a rough

by conventional machining processes

finish. After this a new tool is used at a

or wire EDM.The tooling is relatively

much slower cutting rate, which can be

inexpensive, but for precision parts new

as low as 2 mm3 (0.00012 in.3) per minute,

tools are required for each operation.

to produce a very fine finish. Therefore,

Different factors affect cycle time for wire and die sink EDM. In wire EDM applications, cycle time is affected by

very fine surface textures are best suited to small surface areas. Labour costs are moderate due to the

the thickness of the material.Thicker

high level of operator skill required and

materials require higher power and

the length of the process.

consume more wire electrode. As a rough guide, a piece of 36 mm (1.42 in.)

ENVIRONMENTAL IMPACTS

hardened steel can be cut at 1.5 mm

This process requires a great deal of

(o.osgin.) per minute.This will produce

energy to vaporize the metal workpiece.

an even, matt finish. Slowing the process

However, it does eliminate the need for

down, or using multiple passes, will

any further processing, such as abrasive

produce a finer texture. Speeding the

blasting (page 388) or photo etching

process up will produce a rougher

(page 392). The electrically insulating fluids are

surface finish.

Similarly, the cycle time of die sink EDM is determined by the size of the

continually recycled for reuse. The metal

cutting area and desiredfinish.Typically,

Fumes are given off during operation,

internal geometries are roughed out

which can be hazardous.

at between 200 mm3 and 400 mm3

(image 5). The accuracy of the part is

this case study. This collection of images principles of which can be applied to all

20oC (680F). The water is continuously

After cutting, which takes approximately 2 hours, the part is removed and cleaned

electrodes are also suitable for recycling. Featured Manufacturer

Hymid Multi-Shot www.hymid.co.uk

Cutting Technology

Punching and Blanking Circular, square and profiled holes can be cut from sheet materials using a hardened steel punch. Tooling is either dedicated or interchangeable, depending on the geometry and

INTRODUCTION Punching and blanking are shearing processes used in metalworlc.They are essentially the same, but the names indicate different uses: punching refers

complexity of design.

to cutting an internal shape (see images,

below and opposite) and blanking is cutting an external shape in a single Costs

Typical Applications

Suitability

• Low to moderate tooling cost • Low to moderate unit costs

• Automotive and transportation • Consumer electronics and appliances • Kitchenware

• One-off to mass production

Quality ¦ • High quality and precise, but edges require 1 de-burring

Related Processes

Speed

• CNC machining • Laser cutting • Water jet cutting

• Rapid cycle time (1-100 per minute) • Tooling changeover is time consuming

operation.

Above left Above

multiple punches around the perimeter

RELATED PROCESSES

removing large areas of material from

of the cut string together in a process

These processes can only be used for

the centre of the workpiece (punching)

known as 'nibbling'.

thin sheet materials up to 5 mm (0.2 in.).

and leave ahole of on a rotating die to

Water jet cutting (page 272) andlaser

exactly the same shape. accommodate its profile.

Cutting out large parts (blanking), or

becomes impractical with a single tool

Another operation, known as

These figures are The perforation on the

punched from Alessi Max Le Chinois colander stainless steel products is punched in 2 stages

above 85 mm (3.35 in.) diameter because

'notching', is the removal of material

cutting (page 248) are suitable for a

it would be too expensive. In such cases

from the outside of the workpiece.

wide range of materials and thicknesses.

will increase investment cost. It may also

Small cuts can be made more quickly by

have to be carried out in several stages

referred to as punching.They are often

punching because each cycle removes

because punching can only occur in the

combined in a production line such as

a chunk of material, whereas laser and

vertical position.Thus, Max Le Chinois

progressive dies in metal stamping (page

water jet have to trace the outline.

(see image, above), the Alessi colander

82). In other applications, punching may

CNC machining (page 182) of

designed by Philippe Starck, requires 2

These processes are generically

be the core process, in which case the

holes and profiles is more precise,

punches: 1 forthe perforations on the

operations are carried out on a punch

but consequently more expensive. A

side and 1 for the base. The product is

press, or turret punch. A punch press uses

machining operation, such as drilling

punched and rotated in stages until the

a single tool and is typically set up for a

or milling, will produce perpendicular

full circumference is complete.

repetitive operation. A turret punch is

walls without burr, but cycle time is

coijiputer controlled, and is loaded with

con si derably longer.

multiple tools that can accommodate

Turret punches can be used to

prototype parts without investing in expensive tooling. A typical

complex and varied operations, including

QUALITY

metalworking factory will have many

nibbling. Flypressing is a manually

The shearing action forms'roll over'on

tools for cutting a range of profiles

operated spinning press.

the cut edge andfractures the edges

guided by computer.

of the material.This results in burrs,

Punching tends to be used to

TYPICAL APPLICATIONS

which are sharp and have to be removed

Some typical products include

by grinding and polishing (page 376).

perforations orfixing points. It is also

kitchenware, such as Alessi colanders,

Problems are minimized by careful tool

used for decorative applications because

bowls and plates, consumer electronic

design and machine set up.

a punched hole, for example, does not have to be circular or square.

and appliance enclosures,filters, washers, hinges, separators, general metalwork

add function to a metal part such as

DESIGN OPPORTUNITIES

Selective material removal will reduce

It is not just flat sheet that can be

weight but may not reduce strength too

punched. Stamped, deep drawn (page

much.Therefore, it is sometimes practical

in low volume and prototype production

88), roll formed (page no) and extruded

to carry out functional punching and

of parts that will ultimately be shaped by

metal parts are also suitable. Specialized

selective material reduction on an item

processes such as stamping.

tooling is required for 3D parts, which

in the same operation.

and automotive body parts. These processes are used a great deal

ro Os

DESIGN CONSIDERATIONS

Punching and Blanking Process

The first consideration is the width of material being removed or left behind. Punch diameter or width should be not

Hydraulic ram i or fly press

smaller than material thickness. Also, the

width of material left behind should be greater than the thickness of material. Fixing points should be inset as far as possible for maximum strength.

Workpiece

n I l

Case Study

Punch pressing the Alessi Tralcio Muto tray Punch

1 Stripper

Scrap or workpiece

1 Die

move about during production, but are

sufficiently fragile to allow the parts

Cutting edge Roll over and burr Scrap or workpiece

to be broken outby hand. The burr left it is concealed in a recess.

Stage 1: Loading

to 0.75 mm (0.01- 0.03 in.). Therefore,

carried out on a turret punch, punch press

the sides of the hole are not exactly

Almost all metals can be processed in

or flypress. It is possible to punch a single

perpendicular to the face.

this way. It is most commonly used to

hole, multiple holes simultaneously, or

cut carbon steel, stainless steel and

many holes with the same punch.

Other materials, including leather, also be punched, but metalworking machinery is not suitable. These materials are softer and easier to cut than metal. Punching in this case is

punched again to produce the complete

Sansoniin 2000.

pattern (images 7 and 8).

In stage 1, the workpiece is loaded onto the roller bed. In stage 2, the

surface. This is to ensure that the tray can

be polished to a very high finish. If it were

at a time (image 4). The design is such that

punched from the front, the edges of the

the punching operation is carried out in 2

holes would have a slight radius from the

stages.There is too much cutting for a single

impact and so could not be polished to

stroke on this 150 tonne (165.35 US ton) press.

such a high level.

Once cut, the punch retracts and the

free. Either the punched material or the surrounding material is scrap, depending

stripper and die clamp the workpiece.

on whether it is a punching or blanking operation. In both cases the scrap is

causing the metal to fracture between

collected and recycled.

the circumferences of the punch and die.

Dedicated tooling may be made up

The die is slightly larger than the punch

of many punches joined together. They

to allow for roll over and burr caused

operate simultaneously in a punch press.

typically referred to as die cutting (page 266), which is the process of making all

by the shearing process. The offset is

Complex and intricate shapes are more

determined by the type and thickness

easily achieved with these tools such as

the cuts in a single stroke.Thin metal

of material and ranges from 0.25 mm

in the Alessi case study.

sheet is also suitable for die cutting.

COSTS Standard and small tools are inexpensive.

ENVIRONMENTAL IMPACTS

Specialized and 3D tools can be more

Parts can be nested very efficiently on

expensive but are suitable for small

a sheet to minimize scrap. Any scrap is

batch production. Cycle time is rapid. Between 1 and 100 punches can be made every minute,

but this depends on loading time

collected and separated for recycling, so there is very little wasted material. The de-burring process is abrasive and so produces some waste.

and continuity of production.Tooling changeover time can be expensive. Labour costs are moderate to high because these processes require skilled operators to ensure high quality cuts. Machine set up determines the quality and speed of cut.

so that the burrs are on the flat front

Trays are loaded into the tool (image 3) one

stripper ensures that the metal comes

The hardened punch stamps through it,

The tray is punched from the back

part is coated in a thin film of oil (image 2).

TECHNICAL DESCRIPTION The operation is the same whether it is

textiles, plastic, paper and card, can

which was designed for Alessi by Marta

Stage 2: Punching

COMPATIBLE MATERIALS

aluminium and copper alloys.

and the product is rotated through go" and

edges are trimmed, de-burred and rolled. The

n n 1 1

These ensure that the part does not

behind will have to be polished off, unless

The first punch is made (images 5 and 6)

production of the Tralcio Muto tray (image l),

The tray is stamped in stainless steel; the

Parts that are cut out have to be tied into the sheet of material by tabs.

This case study illustrates a stage in the

Featured Manufacturer

Alessi www,ales5i,com

The final part is removed from the too! and taken to be polished (image 9),

Case Study

The turret punch is loaded with a series of

Each cycle produces a small piece of scrap,

The cut out part is inspected and cleaned

matching punches and dies (image i).The

which is siphoned into a collection basket for

up (image 5). Tabs maintain the blank in the

orange surround on the punch is the stripper,

recycling (image 4). In a blanking operation,

sheet until it is further processed (image 6).

which makes sure the punch can retract from

these pieces of metal are the workpiece. Many

In this case, the metal blanks are formed into

the wofkpiece.

of the pieces, such as squares and circles, are

enclosures by press braking (page 148).

The die set is loaded into the turret and

from straightforward punching operations.

their location programmed into the computer

The crescent shaped part was produced by a

guiding software (iinage 2). Optimization

nibbling operation, in which a circular punch

software ensures that the punch selected

makes a larger diameter hole with many

is the most efficient for each cut. Many

overlapping cuts,

different tools may be used for a single part, all of which are pre-loaded into the turret.

Changeover time can be lengthy, and all the while the machine is not working it is losing money.

Parts are nested together on a sheet to minimize scrap. The punching operation takes less than 2 minutes for these parts (image 3). The sheet is moved around on the roller bed and the turret rotates to select the die set for each operation.

Featured Manufacturer Cove Industries www.cove-industries.co.uk

ttm Cutting Technology

Die Cutting Using die cutting, thin sheet materials can be cut through, kiss cut, perforated and scored in a single operation. It is a rapid process and is utilized a great deal in the packaging industry for mass producing cartons, boxes and trays.

Low tooling costs Low unit costs

INTRODUCTION

The depth and shape of each steel rule

This process, which is also referred to as

determines whether it cuts through,

blanking, is a stamping process in which

kiss cuts (in which the top layer is cut

shapes are cut from sheet material using

through and the support layer is left

steel knives mounted on wooden tools.

intact), scores or perforates the material.

It is the opposite of punching (page 260),

Typical Applications

Suitability

• Packaging • Promotional material • Stationery and labels

• Low to high volumes

Quality

Related Processes

Speed

• High quality edge finish

• Laser cutting • Punching • Water jet cutting

• Very rapid cycle time (up to 4,000 per hour)

which is the removal of material from the

TYPICAL APPLICATIONS

workplace by a similar action.

This process is primarily used in the

Die cutting, which is carried out as

packaging industry. The number and

a linear or rotary operation, is the most

angle of lines does not affect the

cost effective way to cut complex net

operating cost, so it is ideal for packaging

shapes from most non-metallic sheet

systems that have intricate details or

materials,including plastic, paper,

complex shapes and are not based on

card,felt andfoam. It combines many

right angles. Many boxes, cartons and

operations into a single stamping action.

trays are made in this way. A major area of application is cutting out labels, including pressure Other stationery applications are

Top This is the steel rule wooden die used for

plastic and paper folders, envelopes and

the Libellule light

promotional material. Lighting products

(page 269).

sensitive and adhesive backed ones.

are also made using die cutting. This process lends itself to low volume production, as low as 50 parts, because of its relatively inexpensive tooling.

Above

The foam pads that surround the sharp

blades eject the cut or perforated material.

RELATED PROCESSES

over large volumes.The cutting action is

Testing is essential to eliminate such

Die cutting is the process of choice for

between a sharp cutting rule and a steel

aesthetic defects.

most non-metallic and non-glass flat

cutting plate, and therefore results in

sheet cutting applications. Sheet metals

clean, accurate cuts. Scoring, kiss cutting

DESIGN OPPORTUNITIES

are cut into similar shapes by punching,

and perforating are equally precise, and

The complexity of a design does not

water jet cutting (page 272), laser cutting

the depth of cut is accurate to within

affect the cost of die cutting -unlike

(page 248) or simply with a guillotine. Sheet glass is typically scored (page 276)

50 microns (o.ooig in.). Accuracy also

many mass production techniques in the

depends on the material being die cut:

packaging industry such as the printing

or water jet cut.

for example, corrugated materials have

and rotary slotting machines used to

a unidirectional core pattern that may

produce cardboard boxes.Therefore,

affect scored bends.

designers are free to explore innovative

QUALITY The tools used in die cutting are

Some materials resist certain cutting

structures such as closures, handles and

typically laser cut and so precise. The

techniques, especially kiss cutting.

display windows in packaging without

steel knives wear very slowly and have

Cutting such materials may result in

fear of ramping up the cost.

a long lifespan.The quality of the cut is therefore very high and repeatable

a halo around the perimeter, or cause laminated materials to delaminate.

The size of the product is also

insignificant because multiple small

TECHNICAL DESCRIPTION

Die Cutting Process Sheet material

Die cutting consists of 3 main elements: Perforated cutting rule

the steel rule wooden die, the press

Cutting rule

Score rule

Case Study

Angle score rule with lower die

Die cutting the Libellule light

either side of it and the sheet material to be cut.

Support plate

Steel rules are mounted in a

u Ju n

I Steel rule I wooden die

wooden die. The slots for the rules are

typically laser cut. If the blades wear

| Cutting plate

out then they can be easily replaced.

This Libellule pendent light was designed

which the cut shapes are easily removed

by Black & Blum (image 1). Because the

from the sheet (images 5 and 6), which

volumes for this product do not justify

becomes scrap material (image 7).

fully automated production, it is made on a manually operated die cutting machine

The steel rules pass right through the i Hydraulic ram

wooden die and press against the steel

Foam pads

(image 2). To reduce weight and maximize production efficiency, 2 shades are produced

support plate. This ensures that all of

on each piece of polypropylene sheet, which

the energy produced in the hydraulic

is cut to size (image 3).

Stage 1: Loading

rams is directed Into the cutting or

Each cycle requires the operator to load

scoring action.

and unload the cut sheet (image 4), after

The pressure required for cutting is determined by the thickness and type of material. It is also sometimes

possible to cut through multiple sheets simultaneously. Generally, the pressure

required to die cut is between 5 and 15 tonnes (5.5-16.5 US tons), but some

die cutters are capable of ^00 tonnes (441 US tons) of pressure. In stage 1, the sheet is loaded onto Stage 2; Die cutting

the cutting plate, which rises up to meet the steel rule wooden die. In stage 2, the

sharp steel rules cut right through the shapes can be mounted onto a single die,

operating on x andy axes.This same

pads either side of each cutting rule

maximizing output. Cutting beds can

process is used to cut fabric patterns

apply pressure to the sheet material to

typically accommodate sheet materials

for upholstery (page 338) andfibre

prevent it from jamming. The cutting

up to 1.5 x 2.5 m (5 x 8 ft).

reinforcement for composite laminating

sheet material, while foam and rubber

action is instantaneous, each sheet

A multitude of materials can be die

being processed within a few seconds.

cut. This means that an entire packaging

However, particularly tight and complex

system can be shaped in this way,

(page 206).

DESIGN CONSIDERATIONS

geometries can clog up the die, in which

including the card enclosure and foam

Thetypeofmaterial will determinethe

case the operator may have to remove

padding, for example.

thickness that can be cut.

material manually.

Multiple operations are performed

Possible shape, complexity and

It Is possible to score certain

simultaneously. Materials can be cut

intricacy are determined by the

materials, such as corrugated card

to specific depths in increments only

production of the steel rule dies. Steel

microns apart, such as in kiss cutting,

rule blades can be bent down to a 5 mm

and plastic, using different techniques, including perforating and creasing, and by adding a ribbed strip on the cutting plate. The type of steel rule used to score the material is determined by the angle and depth of score required.

which is used for the production of

(0.2 in.) radius. Holes with a smaller

self-adhesive labels on a backing

radius are cut out using a profiled punch.

film. Because these operations have

Sharp bends are produced by joining 2

to be extremely precise (within 50

steel rules together at the correct angle.

microns/o.ocng in.), they take longer to

The width between the blades is

set up and require skilled operators to

limited to 5 mm (0.2 in.); any smaller and

control the tools.

ejection ofmaterial becomes a problem.

Prototyping in sheet materials is

Thin sections should be tied into thicker

generally an inexpensive process. Most

sections to minimize ejection problems.

cutting operations are carried out on a

Nesting parts is essential to reduce

CNC x- andy-axis cutter, which transfers vector based CAD data to a cutting head

material consumption, cycle time, scrap material and costs in general.

Featured Manufacturer

PFS Design & Packaging www.pfs-design.co.uk

Case Study

Die cutting and assembling a crashlock box This crashlock cardboard box (image i) is

with the adhesive fully cured, flat and ready

produced in very large numbers and so

to ship (image 8).

production is fully automated. It is called

This particular set-up is not dedicated,

a 'crashlock' because the base is glued

and most of the mechanisms are computer

together in such a way that It unfolds as

controlled. Therefore atthe click of a button

the box is opened up.

they move into place ready for the next

Die cutting is the most effective method

sequence of events. However, setting up the

of manufacturing the box because there

process for the first time is still a long and

are angled cuts and scores that cannot

highly skilled job.

be produced on printing and slotting machines. Very simple boxes that are scored

and cut at right angles can be produced economically with rotary cutters on the end of the print line. However, as soon as there is an angle to score, such as on

the base of the crashlock box, die cutting techniques are used.

Large quantities of card are needed for this production process that requires 4,000 feeds per hour (image 2). The card is die cut in an enclosed production line, after which is it fed onto the folding production line (image 3).This is an incredible and rapid process, which is hypnotic to stand and watch. The combination of levers, arms,

rollers and glue dispensers gradually assemble the boxes (images 4-7). The finished boxes emerge from the press,

COMPATIBLE MATERIALS

more parts, which means a cycle time of

the material supplier. In some cases

Many materials can be cut by die cutting,

16,000 parts per hour.

the offcuts can be recycled by the

Labour costs are low in automated

manufacturers themselves, such as In

sheet, plastic film, self-adhesive films,

systems. Manually operated production

thecaseofCullen Packaging, who use

cardboard, corrugated card, board, foam,

is restricted to low volume parts and is

the scrap material from their cardboard

including corrugated plastic, plastic

rubber, leather, veneer, felt, textile, very

slightly more expensive, but operation is

packaging facility as raw material in their

thin metals, fibreglass and other fibre

rapid and needs little adjustment or

paper pulp production plant (page 204).

reinforcement, flexible magnets, cork,

maintenance. Set-up can be expensive in

vinyl and DuPont™Tyvek®.

both automated and manually operated versions, due to the machine down time.

COSTS Tooling costs are low.Tools are usually

ENVIRONMENTAL IMPACTS

wooden based and wear out very slowly.

Die cutting does produce offcuts.

Cycle time is very rapid. Automated

However, scrap can be minimized

systems can operate at up to 4,000 feeds

bynesting the shapes together on a

per hour. Each feed may produce 4 or

sheet. Most scrap can be recycled by

Featured Manufacturer

Cullen Packaging www.cullen.co.uk

7

I

Abrasive Water Jet Process High-pressure water feed

4 A high-pressure jet of water, which is typically mixed with

thickness. For example, polymer foam

abrasives, produces the cutting action. It will cut through almost

100mm (3.94 in.) thick will cut with very little drag, but the maximum thickness

any sheet material from soft foam to titanium, and is capable of

for stainless steel is 60 mm (2.36 in.) and the cycle time is considerably longer.

cutting stainless steel up to 60 mm (2.36 in.) thick.

One-off to medium volumes can be accommodated because there are no tooling costs. Also, the scale of the

1 No tooling cost Moderate unit cost

Typical Applications

Suitability

workpiece does not dramatically increase

• Aerospace components • Automotive • Scientific apparatus

• One-off to medium volumes

costs.Therefore, this process is ideal

Nozzle

for prototyping and experimentation. Materials can be changed and tested

Quality

Related Processes

Speed

• Good quality

• Die cutting • Laser cutting • Punching and blanking

• Moderate cycle time, depending on the type and thickness of material

without any start-up cost because the main cost factor is time. External and internal profiles can be cut in the same operation. Entry holes are unnecessary, except in materials that are

INTRODUCTION

industries were the early adopters.

QUALITY

This is a versatile process for cold cutting

However, this process is now an

One of the main advantages of water

The process does not create stresses in

sheet materials. It has been used for

essential part of many factories. Specific

jet technology is that it is a cold process;

the workpiece, so small, intricate and

commercial industrial applications since

applications include cutting intricate

therefore it does not produce a heat-

complex profiles are possible.

the 1970s andhas continued to develop

glass profiles for scientific apparatus,

affected zone (HAZ), which is most critical

at a rapid pace. It is carried out as either

titanium for aerospace and carbon

in metals. This also mean s that there is

DESIGN CONSIDERATIONS

TECHNICAL DESCRIPTION

water only cutting or abrasive water jet

reinforced plastic for motor racing.

no discolouration along the cut edge and

Reducing cycle time reduces the cost of

This is only a small part of the equipment

pre-printed or coated materials can be

the water jet process. Sharp corners and

required to produce water jet cutting. Tap

or increasing the water pressure. The

tight radii slow down the process; the water jet cutter will slow down to avoid

water is supplied to the cutting nozzle

same techniques will reduce drag and

at very high pressure from a pump and

other cutting defects, which are especially

intenslfler combination. In the pressure

prominent on internal and external radii.

cutting. Water only cutting is ahighvelocity jet of water at pressures up to

RELATED PROCESSES

4,000 bar (60,000 psi).The supersonic jet

This process competes with a diversity

of pure water erodes the materials and produces the cutting action. In abrasive

of machining operations as a result of

the diversity of compatible materials.

cut this way. Pure water jet produces a much cleaner cut than abrasive systems. In both operations, there is no contact

likely to delaminate or shatter on impact.

drag, which inadvertently increases cut taper on curves. Also, holes with

chamber the water reaches up to 4,000

decreased by reducing the cutting speed

The difference between this process

bar (60,000 psi). At this high pressure It

and pure water jet cutting Is the addition

Is forced through a small opening In the

of abrasive particles. Without the mineral

water jet cutting small particles of sharp

Laser cutting (page 248), die cutting

between the tool andworkpiece and so

material are suspended in the high-

there is no edge deformation. However,

velocity jet ofwaterto aidthe cutting

(page 266), punching and blanking (page 260) and glass scoring (page 276) are all

process in hard materials. In this case the

alternatives for profiling sheet materials.

due to reduced pressure and so produces

water jet cutting vary in size much like

cutting action is executed by the abrasive

Laser cutting is suitable for a range of

a rougher finish. The process is slowed

sandpaper (120,80 and 50). Different

particles as opposed to the water. Both

materials, but produces a heat-affected

down to accommodate this in harder

This water Is continuously sieved, cleaned

zone (HAZ). Die cutting and punching

materials, which increases cycle time.

grit sizes affect the quality of the surface finish; finer grit (higher number) is

mineral particles (often garnet! are fed

are very accurate and work to tolerances

Into the mixing chamber and come Into

and recycled.

of less than 500 microns (0.02 in.).

and blanking are used to cut a wide

slower and produces a higher quality

contact with the supersonic water, which

surface finish.

propels them at very high speed towards

TYPICAL APPLICATIONS

the flow of water drags in deep materials

range of thin sheet materials. Glass

DESIGN OPPORTUNITIES

scoring is only suitable for thin materials.

This process cuts most sheet materials

a diameter smaller than the depth of material should be drilled. The sharp particles used in abrasive

The final accuracy of the part is

'orifice' (0.1 to 0.25mm In diameter). This

particles it Is the water alone that erodes

Is also sometimes called a jewel because

the workpiece.

It Is made of diamond, sapphire or ruby.

In abrasive jet water cutting the sharp

the workpiece. The abrasive particles

Applications for this process are diverse.

between 0.5 mm and 100 mm (0.02-

determined by a combination of many

create a beam 1 mm (0.04 in.) In diameter,

As with most new technology, the

3.94 in.) thick. The hardness of the

factors including material stability,

which produces the cutting action. The

aerospace and advanced automotive

material will determine the maximum

thickness and hardness, accuracy of

taper left by the cutting process can be

The high velocity jet Is dissipated by the bath of water below the workpiece.

Water jet cutting glass The water jet cutter is CNC, so every

operation is programmed into the machine from a CAD file (image i). The discs are being cut from 25mm (0.98 in.)

plate glass.The cutting nozzle progresses slowly around the workpiece to achieve a clean cutting action. As it progresses,

the operator inserts wedges to support the part as it is being cut (image 2). This image clearly shows the drag on the high-velocity jet of water as it erodes the material. The faster the cutting process, the greater the effect of drag and subsequent drop in quality. After cutting, the part is carefully removed. The cutting programme is

designed to overrun at the start and end of the process to ensure a perfectly symmetrical disc (image 3). The surface finish that is left by the abrasive water jet cutting action (image 4) is improved by polishing, which takes place on a diamond encrusted polishing wheel (image 5). Finally, a small chamber is ground onto the cut edge (image 6).

the cutting bed, consistency of water

but it is possible to cut wood and other

process does not cause these problems.

ENVIRONMENTAL IMPACTS

pressure and speed of cut.

natural materials.

Even printed and coated materials can

The kerf is quite narrow and so very little

be cut without any detrimental effects to

material Is wasted during operation.

the surface.

Offcuts In most materials can be recycled

Very thin materials may break before

Mild steel, stainless steel and tool

the cutting process has finished due to the weight of the part on the uncut

Titanium, aluminium, copper and brass

steel can all be cut with high accuracy.

or re-used. Computer software Improves

material. Tabs can be designed in to avoid

are suitable for complex profiles and

COSTS

efficiency by nesting parts together to

this, or wedges inserted to support the

can be cut rapidly with this process

There are no tooling costs.

produce minimal waste. Water jet does

part.Tabs mean secondary operations

compared to other cutting technologies.

because they will have to be removed afterwards.

Marble, ceramic, glass and stone can

be cut into intricate profiles even though they are quite brittle.

COMPATIBLE MATERIALS

Laminates and composite materials

There are very few materials that cannot

(including carbon reinforced plastic)

be cut in this way. The first water jet

can be cut very effectively. Laminated

cutting was developed to machine wood.

parts tend to delamlnate under stressful

Cycle time can be quite slow but

not produce a HAZ or distortion, so the

depends on the thickness of material and

parts can be nested relatively closely and

quality of cut.Thin sheets of material

as little as 2 mm (0.079 ,T1-) apart.

can be stacked up and cut In a single operation to reduce cycle time. Labour costs are moderate due to the skilled workforce that Is required.

There are no hazardous materials created In the process or dangerous vapours off-gassed. The water is usually tapped from themains andis cleaned and recycled for continuous use.

Featured Manufacturer Instrument Glasses www.instrument-glasses.co.uk

Very little wood is now cut in this way.

cutting conditions, and the water jet

TECHNICAL DESCRIPTION

Glass Scoring Process

Glass scoring can be carried out by hand or on a computer-guided x-y plotter. This diagram shows computer-guided scoring.

Attached to the rotating head is a

Cutting Technology

Rotating head

tungsten carbide cutting wheel. Low

Glass Scoring

pressure is applied to the cutting wheel as it runs across the surface of the glass. Glass workpiece

This is a precise method for cutting sheet glass materials. The

INTRODUCTION

cutting wheel is guided along x and y axes at high speed from a

Class scoring is the most widely used

Cutting wheel

just ahead of the cutting wheel. This crack is known as a median or vent crack and is

typically less than 1 mm (O.O^i in.) deep.

technique for shaping and sizing

CAD file to produce one-offs or high volumes of parts.

Stage 1: Score

sheet glass from 0.5 mm to 20 mm (0.02-0.8 in.) thick. It is used for both

Applying pressure to the glass forces the Median crack

manufacturers and craftsmen alike Suitability

1 No tooling costs 1 Low unit costs

• Furniture • Glass panes and tiles • Stained glass

• One-off to high volume production

Quality

Related Processes

Speed

• Good quality cut edge, but with some lateral cracking

• Laser cutting • Water jet cutting

• Rapid cycle time (roughly 100 m/328 ft per minute)

shallow crack to extend through its depth and the parts are broken out.

utilize this process for general sheet Typical Applications

Once the operation is complete, the glass sheet is removed from the cutting bed.

industrial and decorative applications:

Costs

This produces a flaw that forms as a crack

This method produces a good quality

cutting operations.

cut edge. The median crack caused by the

cutting wheel is a different texture to the

Carried out on a computer guided x-y

plotter, this is a high speed and precise

Stage 2: Breakout

break (see image, opposite).

cutting technique. Handheld scoring tools are also widely used, especially for simple, long and straight cuts.

TYPICAL APPLICATIONS

DESIGN OPPORTUNITIES

COMPATIBLE MATERIALS

Display screens,tabletops, lenses, filters,

The main advantage for designers is

All types of sheet glass can be cut such as

protective glass covers and glass signage

the speed and versatility of this process.

float glass, textured, coloured, mirrored

are just a few of the wide range of

Designs can be prototypedfreehand,

and dichroic glass.

products made in this way.

with a compass, or around a profile. In

This is the main technique for cutting out stained glass designs.

production, the design is cut from sheet

COSTS

by a computer guided cutting wheel.

There are no tooling costs.

Small shapes are possible in thin

RELATED PROCESSES

materials. For example, disks down to

Waterjet cutting (page 272) andlaser cutting (page 248) are also used to profile

5 mm (0.2 in.) in diameter are feasible.

sheet glass materials. They are both

DESIGN CONSIDERATIONS

slo,werthan scoring for simple external

This process is limited by what can

Cycle time is rapid, and cutting speeds

Of loo m (328 ft) per minute are typical. Labour costs are low for automated operations and high for manual processes such as stained glass.

profiles, but are capable of cutting

be broken out of the glass sheet. It is

ENVIRONMENTAL IMPACTS

through a wide variety of materials and

possible to cut simple straight or curved

No glass is wasted in this operation: all

thicknesses. Class scoring is suitable for

lines of any length, but internal shapes

offcuts can be recycled.This is a verylow

materials up to 20 mm (0.8 in.) thick. By

cannot be made, only external profiles.

impact process, which requires very little

contrast, waterjet cutting is capable of

Each score must run from edge to

energy in operation. Unlike waterjet cutting, this process

cutting sheet glass up to 70 mm (2.75 in.)

edge, or as a continuous shape.Therefore

thick. Laser cutting produces a very high

it is ideal for cutting out disks, rectangles

does not remove a kerf width from

surface finish on the cut edge with less

and simple irregular shapes. But designs

the material.Therefore, parts can be

defects than other cutting methods.

with indents in the profile, such as a

n ested closer together, further reducing

crescent shape, cannot be easily made.

material consumption.

QUALITY

Also, acute angles and complex shapes

The scoring technique produces a clean

are not practical because it may not be

break. However, if the cut edge is exposed

possible to break them out of the sheet in

in application, it should be polished.

a single piece.

I

I U»W^'V*»v\ÿv'»xv"1 v"• V1'V'SVV'

Case Study

Glass scoring dichroic lenses The discs are cut out on a computer guided

shallow. Gentle pressure is applied, which

x-y plotter. A small amount of lubricant is

causes it to 'run'. Straight edges can be broken

sprayed onto the cutting wheel and glass

out by hand (image 3).

prior to cutting (image i). A small median crack forms under the

Circles and other shapes are broken out using 'running pliers' (image 4), These break

tungsten carbide cutting wheel (image 2).The

the glass outside of the desired shape, causing

amount of pressure is adjusted according to

it to fail along the median crack.The shallow

the thickness of material. For example, 20 mm

cracking caused by the wheel is visible in

(0.8 in.) thick glass needs a relatively high

contrast with the 'run'fracture (image 5).

level of pressure to form a median crack large

Scoring causes small amounts of lateral

enough to enable the shape to be broken out

cracking. To give a sense of scale, this sample

afterwards. At this point the crack is very

is only 3 mm (0.118 in.) thick.

Joining Technology

TECHNICAL DESCRIPTION

Manual Metal Arc Welding Process

MMA welding, also known as stick welding, has been in use since the late 1800s, but has seen major Consumable electrode

development in the last 60 years.

Joining Technology

Modern welding techniques use a

Arc Welding

Weld pool Evolved gas shield —

Arc welding encompasses a range of fusion welding processes. These processes can only be used to join metals because they rely on the formation of an electric arc between the workpiece and electrode to produce heat.

No tooling costs Low unit costs

Quality • High quality

Suitability

• Containers • Fabrications • Structures

• One-off to mass production

• Friction welding • Power beam welding • Resistance welding

Speed • Slow to rapid cycle time

Core wire

coated electrode. The coating (flux)

melts during welding to form the protective gas shield and slag. There are several different types of flux

Slag —

and electrode, which improve the

The most common types of arc welding

versatility and quality of the weld.

are manual metal arc (MMA), metal inert

MMA welding can only produce

gas (MIG) and tungsten inert gas (TIG), which are respectively called shielded

short lengths of weld before the electrode needs to be replaced. This

metal arc welding (SMAW), gas metal arc welding (GMAW) and gas tungsten arc

Typical Applications

Related Processes

INTRODUCTION

Weld metal

Flux covering

is time consuming and stresses the welded joint because the temperature

welding (GTAW) in the US. Arc welding

is uneven. The slag that builds up on

also includes submerged-arc welding

top of the weld bead has to be removed

(SAW) and plasma welding (PW). The joint interface and electrode (in

before another welding pass can take

some cases) melt to form a weld pool,

or large volume production, and the

which rapidly solidifies to form a bead of

quality of the weld is largely dependent

weld metal. A shielding gas and layer of

on the skill of the operator.

place. It is not suitable for automation

slag (in some cases) protects the molten weld pool from the atmosphere and encourages formation of a'sound'joint.

MMA, MIG andTIG welding can all be operated manually. PW and SAW are more suited to mechanized systems due

to the bulkiness and complexity of the equipment, but there is a microplasma variant that is suited to manual work.

MIG welding is also very well suited to automation because it uses continuousfeed consumable electrode and separate Above left

Above

An operator uses

An arc is formed

for certain automated applications such

MMA welding to join

as orbital welding of pipes.

steel plate.

between the coated electrode and

shielding gas.TIG welding is only suitable

workpiece.

Left Joining steel pipes with MMA welding.

TYPICAL APPLICATIONS Arc welding is an essential part of the fabrication process, used extensively in the metalworking industries.The various processes are suited to different uses, determined by volumes, material type and thickness, speed and location.

Top A steel joint that has been MMA welded.

Above Coated electrodes are used in MMA welding.

MMA welding is the most portable of the processes, requiring relatively little equipment; it is used a great deal in

«

the construction industry andfor other site applications such as repair work.

Featured Manufacturer

TWI www.twi.co.uk

TECHNICAL DESCRIPTION

Metal Inert Gas Welding Process

a process. Deposition rate is measured

MIG welding is also referred to as semi-

as kg/hour (Ib/hr), and duty cycle as a

automated welding. The principle is the

percentage. MMA has a deposition rate

same as MMA welding; the weld is made

of approximately 2 kg/hr (4.4 Ib/hr) and duty cycle of 15-30%;TIG has a deposition

by forming an arc between the electrode

and the workpiece and is protected by

Gas nozzle

rate of approximately 0.5 kg/hr (1.1 Ib/hr)

a plume of inert gas. The difference

is that MIG welding uses an electrode

Weld pool

continuously fed from a spool and the

and duty cycle of 15-20%; MIG has a

Contact tube

deposition rate of approximately 4 kg/hr (8.8 Ib/hr) and a duty cycle of 20-40%; and SAW has a deposition rate of

Gas shield

shielding gas is supplied separately.

Weld metal

Therefore, MIG welding distinguishes

Consumable electrode

itself from MMA welding through higher

approximately 12.5 kg/hr (27.5 Ib/hr) and

productivity rates, greater flexibility and

duty cycle of 50-90%. Certain metals, such as titanium, can

suitability for automation.

only be welded to like metals. In contrast,

The gas shield performs a number of

functions, including aiding the formation

carbon steel can be welded to stainless

of the arc plasma, stabilizing the arc

steel or nickel alloys, and aluminium

on the workpiece and encouraging the

alloys to magnesium alloys.

transfer of molten electrode to the weld

MIG welding Is limited to materials

pool. Generally the gas is a mixture of

provides an alternative to conventional

welded joints. MIG welding produces a

between 1 mm and 5 mm (0.039-0.2 in.)

argon, oxygen and carbon dioxide. MIG

TIG welding; the equipment is bulkier

neat and continuous weld bead, as can

thick. PW can accommodate the largest

but the weld is more penetrating.

be seen on aluminium alloy metal ship

range of materials, from 0.1 mm upto

Keyhole welding has the advantage of

decks. Steel ship decks are SAW.

10 mm (0.0039-0.39 in.) thick.

speeds.This means it is suitablefor sheet

DESIGN OPPORTUNITIES

processes, arc welding produces a HAZ.

material up to 10mm (0.39 in).

As well as being suitable for batch and

All welding produces residual stress in

is also known as metal active gas (MAG) in the UK when CO2 or O2 are present in the shielding gas. Non-ferrous metals

deep penetration and high welding

require an inert argon-helium mixture.

Due to the nature of SAW it is only suitable for horizontal welding positions.

RELATED PROCESSES

Modified MMA technology can be used

Top

Featured Manufacturer

TWI www.twi.co.uk

Above

An operator uses MIG

Cross-section of a MIG

welding to seal the end of a steel pipe.

welded overlapping joint profile.

Above left Example of a MIC welded tee joint profile.

Opposite MIG consumable

mass production of actual parts, these

HAZ weld area and beyond.The problems

processes make it possible to realize

are caused by a change in structure

complex metal assemblies without

leading to change in properties and

expensive tooling costs. Combined with

susceptibility to cracking.

More recent fusion welding technologies,

profiling operations such as gas,plasma,

including laser and electron beam

or laser cutting (page 248), welding can

workpiece to be connected to an earth

welding (page 288), are providing an

be used to fabricate accurate prototypes.

return to the power source, so that the

alternative to the conventional processes,

MMA is especially useful for quickly

electrical current passes through the

especl ally for thi cker m aterial s th at

fabricating steel structures, whereas TIG

electrode and creates an arc with the

require deep penetration.

welding can be used to produce Intricate

weld pool. If the metalwork is painted or

Other welding processes, such as

and delicate metal fabrications.

All of these processes require the

coated in any way, this will insulate the

for wet underwater welding of pipes and

friction welding (page 294), resistance

other offshore structures.

welding (page 308) and gas welding,

welding can be used in horizontal,

or impossible. Also, assemblies and

are alternatives for certain applications.

vertical and inverted positions, making

fabrications may contain other elements

of all welding operations and is used in

Adhesive technologies are becoming

these versatile for manual operations.

th at coul d be dam ag ed by th e el ectri cal

many Industries, it is used extensively for

more sophisticated, providing Increased

car assembly because it is rapid and

joint strength with no heat-affected zone

DESIGN CONSIDERATIONS

metal contact close to the weld zone to

produces clean welds.

(HAZ), which is sometimes preferable.

MIG welding accounts for about half

•lOOnim-

As with all thermal metal fabrication

The quality and slower speeds of TIG

Theequ1pmentforMMA,MIG andTIG

metal contact and make welding difficult

current, so It is important to mount the Welding Is aline-of-slght process.

create a path of least resistance avoiding

Therefore, parts need to be designed so

the vulnerable parts of the assembly,

welding make it ideally suited to precise

QUALITY

that a welder or robot can get access to

and demanding applications. It may be

The quality of manual arc welding is

manual or fully automated.

largely dependent on operator skill.

the joint.The geometry of the joint will affect the speed of welding. Deposition

Precise and clean weld beads can be

rate and duty cycle (how much welding

steel,iron andnlckel alloys.There are also

formed with MMA, MIG and TIG welding.

is achieved in an average hour, allowing

for set up, cooling, jigging and so on) are

electrodes for welding copper alloys. MIG andTIG welding, PW and SAW can be

used as a measure of the efficiency of

used on ferrous and non-ferrous metals.

There are 3 main types of PW, which

electrode, which also

have different applications. Microplasma

acts as a filler wire during welding.

welding Is suited to thin sheet and mesh materials. Medium current welding

Automated welding operations produce the cleanest and most precise

COMPATIBLE MATERIALS MMA welding is generally limited to

TECHNICAL DESCRIPTION

Tungsten Inert Gas Welding Process

Plasma Welding Process

Plasma welding is very similar to TIG welding. This means that the process

is versatile and capable of welding everything from meshes and thin sheets to thick materials in a single pass. Plasma nozzle

There are 3 main categories of Optional filler material Weld metal

plasma welding, which are microplasma,

Gas nozzle

medium current and keyhole plasma.

Microplasma is operated with relatively

Plasma gas Weld pool ,

Tungsten electrode

low electrical current, so is suitable for Gas shield

Weld metal .

materials as thin as 0.1 mm (0.0039 in.)

Arc

mi

and meshes. Medium current techniques

Tungsten electrode

Shielding gas

are a direct alternative to TIG welding but with deeper penetration. Keyhole

v

welding can be achieved with plasma because of its powerful, small diameter.

The temperature of the plasma is estimated to be between 3000°C and

TECHNICAL DESCRIPTION

6000°C (5432-10832°F). This is capable of penetrating material up to 6mm

TIG welding Is a precise and high quality

amounts of hydrogen can be added to

welding process. It is ideal for thin sheet

produce a cleaner weld that has less

materials and precise and intricate work.

surface oxidization. Hydrogen makes the

The main distinction is that TIG welding

arc burn hotter and so facilitates high

does not use a consumable electrode;

welding speeds, however, it can also

instead, it has a pointed tungsten

increase weld porosity. Helium is more

electrode. The weld pool is protected by

expensive, but helps the arc burn hotter

a shielding gas and filler material can be

and so facilitates higher production rates.

used to increase deposition rates and for thicker materials.

(0.236 in.) in a single pass.

Top Detail ofTIG welded butt joint profile.

Above Automated TIG welding

Submerged Arc Welding Process TECHNICAL DESCRIPTION

in operation.

SAW, like MIG welding, forms the

The shielding gas is usually helium, argon or a mixture of both. Argon is the

Middle

Below

An arc is formed

Joining metal pipe by TIG welding.

between the tungsten

most common and is used for TIG welding

weld by creating an arc between the continuously fed electrode and Flux recycling

workpiece. However, there is no

electrode and workpiece,

steels, aluminium and titanium. Small

need for a shielding gas because the

and the filler material melts into the weld pool

electrode is submerged in a layer of

flux fed to the joint from a hopper. There are many associated benefits

TIG is widely used on carbon steel,

Labour costs are high for manual

of submerging the arc, including the

stainless steel and aluminium, and it is

operations, due to the level of skill

the main process for joining titanium.

Tequired. Some automated versions can

MIG welding is commonly used to join

run almost completely unattended and

steels, aluminium and magnesium.

so labour costs are dramatically reduced.

the joint, the flux is laid down in front

on very thin sheets, meshes and gauzes.

ENVIRONMENTAL IMPACTS

The weld pool is not visible and it is a

COSTS

A constant flow of electricity generates a great deal of heat during the welding

There are no tooling costs unless special

process, and there is very little heat

jigs or clamps are required.

insulation, so it is relatively inefficient.

absence of a visible arc light, spatterLayer of flux

As the welding torch passes along

Certain PW technologies can be used

Cycle time is slow for MMA welding, especially because the electrode needs

to be replaced frequently. MIG welding is rapid, especially if automated, andTIG

and collected for recycling behind. complex operation, so it is generally

SAW insulates the arc in a layer of flux,

producing 5o% thermal efficiency, compared with 25% for MMA welding. This process produces very little waste

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welding falls somewhere in the middle.

free weld area and very little heat loss.

material; slag must be removed.

Right

mechanized. The flux will affect

In submerged arc

the depth of penetration and metal

welding asolidfluxis used, which limits the

deposition rate, so the workpiece must

process to horizontal

be horizontal to maintain the layer of

joints including lap,

flux. However, overlapping, butt and

butt and tee profiles.

tee joint profiles are all possible and frequently used.

Of the powerful welding processes, electron beam welding

are no processes that compete with them in this area.

is capable of joining steels up to 150 mm (5.91 in.) thick and

Arc welding (page 282), however, is an alternative to power beam welding

aluminium up to 450 mm (17.72 in.) thick, while laser beam

for thin sheet applications. For plastics,

welding is mainly used for materials thinner than 15 mm (0.6 in.).

ultrasonic welding (page 302) is an alternative to LBW. LBW can be combined with arc

Costs

Typical Applications

• No tooling costs • Very high equipment costs • High unit costs

• Aerospace • Automotive • Construction

Suitability

welding to increase opportunities for

• Specialist to mass production

production. For example, large structures

leaving absolutely no trace of the process

often have varying joint gaps that

on either surface.

Above

A dear plastic printer ink cartridge laser welded using

cannot be avoided. Because power beam Quality • High strength joint

Related Processes

Speed

• Arc welding • Ultrasonic welding

INTRODUCTION

technologies are not suitable unless

DESIGN OPPORTUNITIES

accurate joint configurations are lined

Power beam welding has many

• Rapid cycle time

metals and thermoplastics from 1 mm to

Clearweld®.

up precisely with the laser or electron

advantages such as increased production

beam, laser-arc hybrids developed for

rate, narrow HAZ and low distortion.

shipbuilding have been used instead.

Another major advantage for designers

TYPICAL APPLICATIONS

These can accommodate variations

is the ability to join dissimilar materials:

has potential applications in waterproof

in joint gap. The combination of high

for example, EBW can be used to fuse

clothing,for example.

Like arc welding, power beam welding

15 mm (0,04-0.59 in.).The many different

LBW is used on a wide range of industrial

joins materials by heating and melting the joint interface, which solidifies to

types of laser technologies include CO2,

applications,including aluminium

powered laser welding with versatile

a range of different metals. As well as

direct diode and Nd:YAG, as well as Yb

car frames (such as the Audi A2),

metal inert gas (MIG) welding increases

joining dissimilar metals, LBW can weld

which until recently has meant that

form a high integrity weld.The difference

disc and Yb fibre lasers. Besides welding,

construction, shipbuilding and airframe

the quality of joints and improves

a range of different thermoplastics to

the workpiece size is restricted by the

is that power beam processes do not

lasers are used to cut and engrave (see

structures. Since the 1970s, it has been

production rates.

one another. Factors that affect material

size of the vacuum chamber. However,

choice include relative melting point and

mobile EBM has been made possible by

reflectivity.

reduced pressure techniques developed

rely on the formation of an electric arc

laser cutting, page 248), and fuse layers

developed for plastics and utilized for

between the welding electrode and

of particles (see rapid prototyping,

joining thermoplastic films, injection

QUALITY

m ol ded parts, textil es an d tran sparent

Both LBW and EBW processes form

components in the automotive, packaging and medical industries.

workpiece to generate heat. Heat is produced by the concentration of energy in the power beam. Both laser and electron beam

page 232). Electron beams are generated in a high vacuum. Electrons are energized using a cathode heated to above 20000C

technologies are capable of establishing

(36320F) and up to two-thirds the speed

a'keyhole'in the workpiece to deliver

of light for normal industrial electron

heat deep into, or through, the joint.

beam guns.The high velocity electrons

Indeed, this ability means they can be

bombard the surface of the workpiece,

It is now possible to weld clear

EBW is carried out in a vacuum,

in the 1990s. It is now feasible to apply

rapid and uniform high integrity welds.

plastics and textiles using a technique

a local vacuum in a small EBW unit that

They have superior penetration and

known as Clearweld®.The Clearweld®

travels aroundthe joint.This has many

so produce a relatively smaller heat-

process was invented and patented

advantages, including on-site welding

th e 19 60s an d h as been used for m any

affected zone (HAZ) than arc welding. A

by TWI, and is being commercialized

of parts too large or unsuitable for the

years in Japan for welding heavy duty offshore and underground piping.The ability of this process to penetrate thick

major advantage of power beam welding

by Centex Corporation.This process is

vacuum chamber.

is its ability to make deep and narrow

particularly useful in applications that

welds. However, this means there is a

demand high surface finish (see image,

DESIGN CONSIDERATIONS

above). The principle is that an infrared

These processes require expensive equipment and are costly to run,

EBW has been in development since

used to cut, machine and drill materials

causing it to heat up and melt, or

materials makes it ideal for construction

huge temperature differential between

as well as weld them together.

vaporize in an instant.The focused

and nuclear applications.

the melt zone and parent material, which

absorbing medium is applied to the

electrons create power densities as high

can cause cracking and other problems

joint region, either printed or film. This

especially EBW which is carried out

focused to achieve power densities above

as 30,000 W/mm2 (1 mm2 = 0.039 in-2)

RELATED PROCESSES

in certain metals, especially high

causes the joint to heat up on exposure

in a vacuum. Both EBW and LBW

loo W/mm2 (i mm2 = 0.039 in.2). At this

in a localized spot. Thus electron beam

Although they are specialized processes,

carbon steels.

to the laser beam. Without the infrared

are automated, and need careful

absorbing medium the laser would

programming prior to any welding.The

high quality joints. In overlapping

pass right through clear materials and

cost and complexity of power beam

Lasers produce light waves that are

LBW in plastics produces extremely

power most engineering materials melt

welding (EBW) produces rapid, clean

LBW and EBW are gradually becoming

or vaporize, and laser beam welding

and precise welds in materials between

more widespread for joining parts in a

(LBW) is therefore suitable for welding

0.1 mm and450 mm (0.004-17.72 in.)

single pass, which would previously have

geometries the laser penetrates the top

textiles. Hermetic seals can be achieved

processes means that they are suitable

been almost impossible to achieve.There

part and affects only the joint interface,

in plastics and fabrics, so this technology

only for specialist applications and

a range of materials, in eluding most

thick, depending on the material.

m 1— o

TECHNICAL DESCRIPTION

Laser Beam Welding Process

In LBW, the COz, Nd;YAG and fibre laser

Laser beam delivered via mirrors or fibre optic cables

beams are guided to the workpiece by a series of fixed mirrors. Nd:YAG and fibre laser beams can also be guided to the

welding or cutting head by fibre optics, which has many advantages. These

laser technologies typically weld at 7 kW, which is suitable for fusion welding 8 mm (0.315 in.) carbon steel in a single pass at up to 1.5 m (5 ft) per minute. These processes can be used for many

different welding operations, including

Workpiece

profile, rotary and spot welding. Spot welding processes have been recorded at rates of up to 120,000 welds per hour.

A shielding gas is used to protect the melt zone from oxidization and contamination. Because of their shorter

Above

Above right A robot manipulates

wavelength, Nd:YAG laser beams can

to 100 mm (3,94in.) thick. Nor are these

COSTS

also be guided with fibre optics. This

processes limited to very thick materials;

There are no tooling costs, but jigs

means that they can cut along 5 axes, as

they are also used to join thin sheet and

and clamps are necessary because of

Right

the head is free to rotate in any direction.

film materials with extreme precision.

the precision required for the welding

The process of NchYAG laser beam welding

The laser beam is focused through a lens that concentrates the beam to a fine spot, between 0.1 mm and 1 mm (0.004-0.04 in.) wide. The height of

the lens is adjusted to focus the laser

process to be successful. Equipment

COMPATIBLE MATERIALS

costs are extremely high, especially for

Many different ferrous and non-

processes that involve EBW.

ferrous metals can bejoined by power

Cycle time is rapid, but set-up will

An operator checks the CO2 LBW equipment.

the Nd:YAG lasers.

commences.

Far right This detail shows the Nd:YAC laser beam welding head while it

beam welding. The most commonly

increase cycle time, especially for large

welded metals include steels, copper,

and complex parts. For EBW each part

melting the workpiece on contact, which

aluminium, magnesium and titanium.

has to be loaded into a vacuum chamber

Below

resolidifies to form a homogenous bond.

EBW, however, is limited to metallic

and a considerable vacuum applied,

Detail of the finished

materials because the workpiece must

which can take up to 30 minutes. Mobile

NdrYAG laser weld.

on the surface of the workpiece. The

high concentration beam is capable of

be electrically conductive.

Aluminium is highly reflective but can be welded with both lasers and electron beams. Certain alloys are more suitable

massproduction.Thep ayoff i s th at th ey

than others for power beam welding,

are very rapid: EBW can produce high

such as 5000 and 6000 series'.

integrity welds at up to io m/minute

Titanium can be power beam welded,

reduced pressure techniques have lowered set-up time and increased cycle time considerably. Labour costs are high.

ENVIRONMENTAL IMPACTS Power beam welding efficiently

(33 ft/minute) in thick sections. For an effective butt weld the joints have to fit tight tolerances and align

but it is highly reactive to oxygen and

transmits heat to the workpiece, EBM

nitrogen.This means that it is more

typically requires a vacuum, which

difficult and therefore more costly to

is energy intensive to create. Recent

with the beam very accurately. As a

weld.Tungsten inert gas (TIG) welding

developments have made it possible to

result, preparation can also be costly and

is used as an alternative but is up to 10

weld steels up to 40 mm (1.57 in.) thick.

time-consuming, especially for large and

times slower than laser welding.

cumbersome parts. Material thickness is much greater for power beam welding than with arc welding. High power EBW can be used to join steel from 1 mm up to 150 mm (0.04-5.91 in.) thick, aluminium up to 450 mm (17.72 in.) thick and copper up

LBW can be used to join most thermoplastics, including

polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polyoxymethylene (POM) acetal and poly methyl methacrylate (PMMA).

However, weld quality and width to depth ratio are diminished.

is in operation.

l

TECHNICAL DESCRIPTION

Electron Beam Welding Process

Electrons are emitted from a heated tungsten cathode. They are pulled and accelerated into the gun column High voltage cathode

at up to two-thirds the speed of light.

Magnetic focusing coils concentrate the

w

beam into a fine stream, which impacts , Electron particles agitated between electrodes

on the surface of the workpiece. The

. Anode

electrons' velocity is transmitted into heat energy on contact, which

11

vaporizes a localized area that rapidly penetrates deep into the workpiece.

Magnetic focus coil

EBW is carried out in a vacuum of lO'MO"2 mbar 10.000000U5-0.000U5 psi). The level of vacuum determines

the quality of the weld because the High velocity beam of electrons Vacuum

IB

atmosphere can dissipate the electron

o

beam, causing it to lose velocity.

aJ CD

Reduced pressure EBW is carried out

at 1-10 mbar 10.0145-0.145 psil, which requires considerably less energy and Workpiece

O z o

time. As the fusion welding is carried Melt zone

out in a vacuum there is very little contamination of the melt zone, which

ensures high integrity welds.

Above

The scale of this electron beam welded gear is shown by the ruler beneath it. Below This cross-section of

NV? Left Apiece of electron beam welding

electron beam welded

joint demonstrates the integrity of a deep weld.

Above

Electron beam welding in progress.

equipment.

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Linear friction welding

Rotary friction welding

Friction Welding Processes

CLamps Workpiece

Stage 1: Load

Stage 1: Load

Interface plasticizes

Forge welding processes are used to form permanent joints in

Plasticized metal Reciprocating motion

metals. There are U main techniques: rotary friction welding

(RFW), linear friction welding (LFW), orbital friction welding (OFW) and friction stir welding (FSW). Stage 2: Friction through \ j Axial pressure rubbing

Stage 2: Friction through rotation

Typical Applications

Suitability

• Aerospace • Automotive and transportation • Shipbuilding

• High volume production

Quality

Related Processes

Speed

• High integrity hermetic seal • High strength joint that can have similar characteristics to base material

• Arc welding • Power beam welding • Resistance welding

• Rapid cycle time that depends on size of joint

RFW. LFW and OFW: No tooling costs FSW: Inexpensive tooling costs Low to moderate unit costs

INTRODUCTION

In the automotive industry, RFW is

The 4 main friction welding techniques

usedfor critical parts including drive

can be separated into 2 groups:

shafts, axles and gears. LFW is utilized to

conventional techniques including LFW,

join engine parts, brake discs and wheel

OFW and RFW processes; and a recent

rims. OFW has not yet found commercial

Weld flash

Weld flash

Stage 3; Axial pressure

Stage 3: Axial pressure

Axial pressure

Olufsen aluminium speakers (see

TECHNICAL DESCRIPTION

images, page 297, above left and left).

The use of RFW Is limited to parts where at least 1 part Is symmetrical around

RELATED PROCESSES Even though the welds are of similar

Another technique uses stored energy and is known as inertia friction welding.

an axis of rotation. In stage 1, the 2

In this process the spinning workpiece

workpleces are secured onto the chucks.

is attached to a flywheel. Once up to

In stage 2,1 of the parts is spun while

speed, the flywheel is left to spin freely.

the other is stationary. They are forced

The parts are brought together and the

derivative, FSW.

application in metals, but is utilized

quality, friction welding is not as widely

LFW, OFW and RFW operations weld materials with frictional heat generated

in the plastics industry (see vibration

used as arc welding (page 282) and

welding, page 298). FSW is used to join

resistance welding (page 308).This

together, and friction between the 2

stored energy in the flywheel spins the

flat panels, formed sheets, alloy wheels,

is mainly because it is a more recent

faces causes the metal to heat up and

parts sufficiently for a weld to form. The

fuel tanks and space frames.

development: for example,TWI patented

plastlclze. In stage 3, after a specified

process Is similar to RFW, except that a

The first commercial application of

friction stir welding only in 1991. It is also

time - a minute or so - the spinning

mandrel Is used to maintain the Internal

The rotary technique (see main image)

FSW was in the shipbuilding industry,

because friction welding is a specialized

stops and the axial force Is Increased to

diameter of the pipe.

was the earliest and is the most common

for welding extruded aluminium

technique, and the equipment costs are

20 tonnes or so. Flash forms around the

of the friction welding techniques.

profiles into large structural panels.

extremely high.

circumference of the joint and can be

principles as RFW. However, instead of

polished off afterwards.

rotation, the parts are oscillated against

by rubbing the joint interface together. The joint plasticizes and axial pressure is applied, forcing the materials to coalesce.

In FSW the weld is formed by a

This has benefits for many industries:

Friction welding does not take the

LFW and OFW are based on the same

rotating non-consumable probe (tool),

for example, the railway one, in the

weld zone above melting point, so this

one another. In stage 1, the 2 workpleces

which progresses along the joint mixing

construction of prefabricated structural

process can join metals that are not

are clamped. In stage 2, the joint Interface

the material at the interface (see image,

components in train carriages (see

suitable for fusion welding by arc or

page 396, above left).

above right). FSW is suitable as it causes

power beam welding (page 288). Friction welding plastics is known as

TYPICAL APPLICATIONS

very little distortion in the welded parts,

vibration welding (page 298).

Application of these processes is

even across long joints in thin sections.

concentrated in the automotive,

Recently, FSW has been introduced

transportation, shipbuilding and

into the consumer electronics industry,

Friction welding produces high integrity

aerospace industries.

such as in the fabrication of Bang &

welds. Butt joints are fused across the

images, page 297, above, top right and

QUALITY

Above

Right

is heated by rubbing the parts together.

This titanium blistc (i-piece bladed disc) for ]et engines is made by linear friction welding.

These beech blocks have been joinedby linear

In stage 3, axial force Is Increased and

friction welding.

maintained until the joint has formed. LFW typically operates at frequencies up to 75 Hz and amplitudes of ±3 mm 10.118 in.). These processes were developed for parts that are not suitable for rotary techniques.

TECHNICAL DESCRIPTION

Friction Stir Welding Process

This process is similar to RFW, LFW

Rotating chuck

and OFW because the metals are

welded by mixing the joint interface. Likewise, there is no consumable wire, shielding gas or flux. However, FSW

differs from the other friction welding techniques because it uses a non-

Backing bar

Probe

consumable probe to mix the metals.

The probe is rotated in a chuck at high speed, pushed into the joint line and progresses along the joint interface, plasticizing material that comes into contact with it. The probe

softens the material, while the Shoulder Plasticized metal

shoulder and backing bar prevent the plasticized metal from spreading. As the probe progresses, the mixed material cools and solidifies, to

Left above and left Bang & Olufsen BeoLab

Above, top right and

aluminium speakers

Lightweight and

consumable, they can run for only up to

were designed by David Lewis and launched

structural aluminium

1000 m (39.4 in.) before they need to be

during 2002.

stir welding, are needed

produce a high integrity weld. Even though FSW tools are non-

above right

panels, made by friction in the production of

replaced. Some techniques run more

train carriages.

than 1 tool in parallel, for a broader

on the equipment and development for the application.

Cycle time is rapid for RFW, LFW and OFW. FSW is the slowest of the friction welding processes because it runs along

the entire length of the joint. Using

weld or for a weld from either side to

FSW, 5 mm (0,2 in.) aluminium can be

form a deeper joint.

welded at approximately 12 mm (0.472

L

DESIGN CONSIDERATIONS

COMPATIBLE MATERIALS

in.) per second.Thick materials will take

Because they are comparatively new, the

Most ferrous and non-ferrous metals

con siderably 1 on g er.

equipment costs for friction welding are

can be joined in this way, including low

still very high.Therefore it is expensive to

carbon steel, stainless steel, aluminium

ENVIRONMENTAL IMPACTS

develop products with these processes

alloys, copper, lead, titanium, magnesium

Friction welding is an energy efficient

in mind unless there are high volumes

and zinc. It is even possible to weld metal

process for joining metals; there are

of production to justify the investment.

matrix composites.

no materials addedto the joint during

This is partly why friction welding is Above left This aluminium butt joint profile is being

Pipes can be joined in a process known

as radial friction welding, which is a

shielding gas.This process generates no

The tool (probe) and

shipbuilding industries and only to a

development on RFW.The difference is

waste; the exception is run-offs in FSW,

buttjoint have been formed in aluminium by friction stir welding.

limited extent elsewhere.

that in radial friction welding an internal

wh ere th e wel d run s from edg e to edg e.

Above right

integrity. Useful material combinations

state welding processes. In other words,

include aluminium and coppe'r, and

theyweldmetalsbelowtheirmelting

aluminium and stainless steel.

point.The heat-affected zone (HAZ) is

from 1.2 mm up to 50 mm {0,047-1.97 in.)

relatively small and there is very little

It is also possible to join materials of dissimilar thickness. Multiple layers

in non-ferrous metals. It is possible to

made it possible to join certain woods,

shrinkage, and thus distortion, even in

stacked up can be welded in a single pass

weld joints up to 150 mm (5.91 in.) deep if

including oak and beech (see image, page

long welds.

with FSW.

welded from both sided simultaneously.

295, right). Although TWI assessed the

Recently, microfriction welding

process in 2005, it is still in the very early

made using friction stir welding.

Use of RFW, LFW and OFW is limited

FSW is suitable for materials ranging

mandrel is used to support the weld area. Recent developments in LFW have

DESIGN OPPORTUNITIES

to parts that can be moved relative to

producing butt, lap, tee and corner joints.

techniques have been developed that are

stages of development. In the future

As the friction welding techniques are

one another along the same joint plane.

It is particularly useful in the fabrication

capable of welding materials down to

this process has the potential to replace

relatively new processes, especially FSW,

FSW, on the other hand, can be computer-

of parts that cannot be cast or extruded

0.3 mm (0.012 in.).

conventional wood joining techniques.

many commercial opportunities have yet

guided around circumferences, complex

such as large structural panels made up

to be fully understood.

3D joint profiles and at any angle of

of several extrusions.

Joint size in RFW, LFW and OFW techniques is limited to less than

COSTS

advantages such as the ability to join

can fuse almost any joint configuration

gravity, and so can be carried out upside

FSW requires tooling, the cost of which depends on the thickness and type of

dissimilar materials without loss of weld

and part geometry. FSW is also capable of

down if necessary.

material; even so, it is inexpensive,The

operation. Combined, these processes

welding such as flux, filler wire or

used extensively in the automotive and

entire joint interface. These are solid

Friction welding offers important

cost of this process is largely dependent

These processes are not affected by

2,000 mm2 (3.1 in.2).

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Vibration Welding Process

Joining Technology

Vibration Welding Homogenous bonds in plastic parts can be created using

INTRODUCTION

RELATED PROCESSES

vibration welding. Rapid linear or orbital displacement

Vibration welding is based on friction

Linear friction welding metal and linear

welding (page 294) principles.The

vibration welding plastic are the same

generates heat at the interface, and this melts the joint material and forms the weld.

Low to moderate tooling costs Low unit costs

Quality

parts are rubbed together to generate

process; both join parts by rubbing them

frictional heat, which plasticizes the

together using linear motion, under axial

joint interface. The process is carried out

force. Ultrasonic welding (page 302) and

as linear or orbital vibration welding.

certain adhesive technologies are

Linear vibration welding uses transverse,

frequently an alternative, especially for thin walled and delicate parts.

Typical Applications

Suitability

reciprocating motion - the vibration

• Automotive • Consumer electronics • Packaging

• Medium to high volume production

occurs in only 1 axis. Orbital vibration welding uses constant velocity motion

Related Processes

Speed

• Friction welding • Hot plate welding • Ultrasonic welding

• Very rapid cycle time (up to 30 seconds]

Ultrasonic welding transfers energy

through the part to thejoint interface.

- a non-rotating offset circular motion

By Contrast, the Vibration process

in all directions.The vibration motion

transfers energy directly to thejoint

occurs equally in both the x andy axes

interface, so does not rely on the ability

and all axes in between.

of the part material to transmit energy.

Stage 2: Closed mold, welding and clamping

Fillers, regrind, colour additives and

TYPICAL APPLICATIONS

contamination all affect a material's

Although this process is typically utilized

ability to transmit energy and so reduce

TECHNICAL DESCRIPTION

in the automotive industry, it is now

the effectiveness of ultrasonic welding

In stage 1 of linear vibration, 1 part Is

but not vibration welding.

placed in the lower platen and the part

speed, identical for all points on

to which it is to be joined is positioned

the joint surface. The movement's

in the upper platen. In stage 2, the heat

orbital character Is produced by three

necessary to melt the plastic is generated

electromagnets arranged horizontally at

steadily becoming more widespread in, for example, medical, consumer

Recent developments include heating

electronics and white good appliances.

the joint interface prior to welding, in a

process similar to hot plate welding

ssisr

(page 320). Combined, these processes

create neat and high strength welds with much less debris, especially important for such applications as filter housings.

QUALITY Vibration welding produces strong

The orbit Is continuous and of constant

by pressing the parts together and

relative angles of 120°. These magnets

vibrating them through a small relative

Influence the movement of the fixture

displacement from 0.7 mm to 1.8 mm

and generate a harmonic movement.

(0.028-0.071 in.) at 240 Hz or a 4 mm

Compensation for the decreasing force

(0.016 in.) peak to peak at 100 Hz in the

of one electromagnet is provided by

plane of the joint under a force of

attraction of the next electromagnet,

1-2N/mm2 (0.69-1.37 psi).

together with a change in direction. This

Heat generated by the resulting

causes rotary vibration of the fixture,

bonds. It is possible to form hermetic

friction melts the plastic at the interface

which ensures a controlled relative

seals for automotive and packaging

within 2-3 seconds. Vibration motion

movement in a frequency between

applications. When certain material

is then stopped and the parts are

190 Hz and 220 Hz and an amplitude

combinations are joined in this way a

automatically aligned. Pressure is

range between 0.25 mm and 1.5 mm

complete mixing of the materials occurs,

maintained until the plastic solidifies

(0.1-0.59 in.) peak to peak.

resulting in a homogenous bond.

to bond the parts permanently with a

Further variables to influence weldability include moisture content and the addition of resin modifiers.

strength approaching that of the parent material itself.

During orbital vibration welding, each point on the joint surface of the moving part orbits a different and distinct point on the joint surface of a stationary part.

Case Study

Linear vibration welding an automotive light In this case study Branson Ultrasonics

case the red reflectors) rises to meet the

parts are held under a measured clamping

are producing a short production run

upper platen (image 5), forcing the parts

force for another 2 to 15 seconds and the

of automotive sidelights. A pair of right-

together at a pressure of 103-207 N/cm2

melted polymer in the joint interface cools

and left-hand sidelights is being molded

(150-300 psi) (image 6). Either hydraulic or

to form a continuous weld. Finally the mold

simultaneously. The red reflectors (image i)

electromagnetic drivers are used to create

platens part to reveal the welded parts held

are placed into the lower platen (image 2),

the vibration in the upper platen. This is

by vacuum in the upper platen.The vacuum is

then the sidelight housings (image 3) are

mounted onto a resonant spring assembly to

released, dispensing the sidelights (image 7).

positioned into the upper platen, where they

ensure that the parts align accurately once

These are quality checked (image 8) and

are held by vacuum (image 4).

the vibration sequence concludes and the

packed for shipping.

During the welding cycle, the lower

polymers resolidify. The welding process lasts

platen holding the stationary part (in this

no more than 2-15 seconds, after which the

DESIGN OPPORTUNITIES

DESIGN CONSIDERATIONS

for products with thin wall sections or

COMPATIBLE MATERIALS

Both linear and orbital vibration welding

Vibration welding is most suitable for

long unsupported walls because they

Thermoplastics (Including amorphous

(ABS), poly methyl methacrylate (PMMA) acrylic and polycarbonate (PC), which can

and semi-crystalline) are suitable for

be welded to one another.

will flex unless supported by the tooling.

when fully automated or Integrated Into a production line.

provide a fast, controlled and repeatable

injection molded and extruded parts.

m eth od of ach 1 evln g a perm an ent stron g

However, 2 essential requirements must

bond between 2 plastic parts.They also

be taken Into account when considering

requires less clamping pressure than

composite m aterl al s, therm opl asti c

COSTS

There are no materials addedto the joint

eliminate the need for mechanical

the process. Firstly, the design must allow

linear methods and so can be used for

films andfabrics can also be welded

Tooling has to be designed and built

to form the weld, which means that this

fastenings and adheslves.

for the required movement between the

more delicate products. It is currently

in this way. Vibration welding Is particularly useful for materials that

specifically for each part, which Increases

process does not generate any waste.

the start-up costs of the process,

are not easllyjoined by ultrasonic welding or adhesive bonding such

especially if the product is made up of multiple parts that need to be joined In

These processes can accommodate

Orbital technology, on the other band,

ENVIRONMENTAL IMPACTS

this process, and some polymer based

parts to generate sufficient frictional

suitable for relatively small parts, up to

parts with complex geometry, whether

heat; the plane of vibration must be flat,

250 mm (9.84in.) in diameter.

large or small, and can be used to create

or at least within 10°. Secondly, the parts

perimeter and internal welds. As long

must be designed so that they can be

applications where the workpiece cannot

as polyoxymethylene (POM) acetal,

this way.

as the parts can be moved relative to

gripped adequately to ensure sufficient

be vibrated, for Instance, as products

each other along the same joint plane,

energy transmission to the joint.

polyethylene (PE),polyam1de (PA) nylon, and polypropylene (PP). Plastic welding is limited to joining like materials. There

between 2 and 15 seconds and clamping

time Is the same. Welding multiple parts

to weld parts up to 500 x 1,500 mm

are a couple of exceptions to the rule

simultaneously can reduce cycle time.

(20 x 59 In.), but It Is not recommended

such as acrylonltrlle butadiene styrene

Labour costs are relatively low, especially

vibration welding can be used.

Linear vibration welding can be used

Vibration welding Is not suitable for

with moving parts in the top section.

Cycle time Is rapid: welding Is typically Featured Manufacturer Branson Ultrasonics www.branson-plasticsjoin.com

Joining Technology

Ultrasonic Welding This process forms permanent joints using ultrasonic waves in the form of high-energy vibration. It is the least expensive and fastest plastic welding process and so is the first to be considered in many welding applications.

Typical Applications 1 Low tooling costs 1 Low unit costs

• Consumer electronics and appliances • Medical • Packaging

INTRODUCTION

TYPICAL APPLICATIONS

Ultrasonic technology includes welding,

Ultrasonic welding in used for a vast

swaging, staking (page 316),inserting,

range of products in many different

spot welding, cutting, and textile and

industries.The packaging industry

film sealing. Welding is the most widely

uses ultrasonics for joining and sealing

used ultrasonic process and is employed

cartons of juice and milk, ice cream tubs,

by a ran g e of in dustri e s, in cl udin g

toothpaste tubes, blister packs, caps and

consumer electronics and appliances,

enclosures.

Suitability

automotive, medical, packaging,

• Batch and mass production

stationery andtoys. It is fast, repeatable and very

Applications in consumer electronics include mobile phone covers and screens, watch bodies, hairdryers, shavers and

controllable.The conversion of electrical

printer cartridges. Applications in the

Quality

Related Processes

Speed

energy into mechanical vibration is

textile and non-woven industries include

1 High quality permanent bond 1 Hermetic seals are possible

• Hot plate welding • Power beam welding • Vibration welding

• Rapid cycle time (less than 1 second) • Automated and continuous processes can form many welds very rapidly

an efficient use of energy. No fillers

nappies, seat belts, filters and curtains.

are required, and there is no waste or contamination. It is safe to use for

RELATED PROCESSES

toys, medical applications and food

Ultrasonic welding is often the first

preparation. Ultrasonic cutting is used

joining process to be considered. If it

to cut cakes, sandwiches and other

is not suitable then hot plate welding

foods without squashing them: the

(page 320, vibration welding (page 298),

high-energy vibrations effortlessly cut through both hard and soft foods. It is

Top and opposite

Above

freedom. For example, products like

TheTSM6 mobile phone by Product Partners

Triangular beads,

mobile phones and MP3 players are

uses ultrasonic welding

directors, are molded

laser welding (see power beam welding,

made up of material combinations that

on the front assembly.

onto each side of

page 288) may be used.

may not be possible with multi-shot injection molding (page 50), or other

also used to seal drinks cartons, sausage skins and other food packaging.

This diversity gives greater design

Above left Ultrasonic welding

known as energy

the joint interface, perpendicularto one another, to maximize

produces hermetic seals

the efficiency of the

in extruded plastic tube,

welding process.

QUALITY

processes. Parts that cannot be molded in

Ultrasonic welding produces

a single operation can be ultrasonically

for instance, those for

homogenous bonds between plastic

joined to produce complex, intricate and

cosmetic packaging.

parts. Joint strength is high andhermetic

otherwise impossible geometries.

The energy director is raised bead

seals are possible.

DESIGN CONSIDERATIONS

of material on one side of the joint. It is

but this can be minimized with careful

The main considerations for designers

design such as housing the joint out of

are type of material (ease of welding) and

generally triangular and is molded inline with the joint or perpendicular to it (see

geometry of the part. There are 3 main

image, above).The role of the triangular

A small amount of flash is produced,

sight or with the provision of flash traps.

types of joint design: straightforward

bead is to minimize contact between

DESIGN OPPORTUNITIES

overlapping material, energy director

the 2 surfaces and therefore maximize

The advantage of ultrasonic technology

and shear joints (see images, page 304).

the energy transferred to the joint. This

is the range of welding processes

The difference is that energy director

reduces the amount of energy needed

and techniques that are available. For

and shear joint techniques have molded

to produce the weld, reduces flash and

example, as well as conventional joining

details to aidthe ultrasonic process.

minimizes cycle time.

ultrasonic welders can spot weld, stake,

Overlapping joints, such as extruded

embed metal components (known as

tube packaging sealed at one end, are the

works on the same principle of reducing

inserting), swage and form joints.

least strong, but are suitably effective for

surface area in the joint to maximize

the application (see image, above left).

efficiency.The difference is that instead

The alternative method, shear joint,

TECHNICAL DESCRIPTION

Ultrasonic Welding Process

Ultrasonic welding works on the principle

to the joint by the workpiece. This generates

into high-energy vibration by means of

frictional heat at the Interface, which causes

piezoelectric discs. Electricity is converted

the material to plastlcize. Pressure Is

from mains supply (50 Hz in Europe or

applied, which encourages material at the

60 Hz in North America) into 15 kHz, 20 kHz,

joint Interface to mix. When the vibrations

30 kHz or 40 kHz operating frequency. The

stop, the material solidifies to form a strong,

frequency Is determined by the application;

homogenous bond.

20 kHz Is the most commonly used frequency Inserting

Energy director

V

FO

fl fi

4

A

Spot welding

Shear joint

The ultrasonic vibrations are transferred

that electrical energy can be converted

The horn in the diagram is shaped to

because It has a wide range of application.

apply vibratory energy to selected areas of

The converter consists of a series of

the joint. Other joining techniques include

piezoelectric discs, which have resistance

energy director, inserting, shear joint and

to 15, 20, 30 or 40 kHz frequencies. The

spot welding. In each case, the red area

crystals that make up the discs expand

Indicates the weld zone. This is barely visible

and contract when electrically charged. In

from the surface, but clear In a microscopic

doing so, they convert electrical energy Into

view (see Image, belowl.

mechanical energy with 95% efficiency.

33

> in o

The mechanical energy Is transferred to the booster, which modifies the amplitude Into vibrations suitable for welding. The horn transfers the vibrations to the workpiece.

o o

2

The size and length of the horn are limited because it has to resonate correctly.

of a triangular bead, the joints are

field welded, meaning the joint is within

Textile and non-woven materials,

Labour costs are generally low. Tooling

5 mm (0.2 in.) of the contact point.

including thermoplastic fabrics,

changeover Is quick and the process is

composite materials, coated paper and

highly repeatable without the need for

to a thin line of contact. As the parts

COMPATIBLE MATERIALS

mixed fabrics, can be joined.

operator intervention.

are pressed together, the shoulder

All thermoplastics can be joined in this

progresses down the joint until the

way. Many amorphous thermoplastics

designed with a shoulder or step.This detail concentrates the vibratory energy

entire interface is welded.

such as acrylonitrile butadiene styrene

Some metals can be joined in this way. However, the technology is more

ENVIRONMENTAL IMPACTS

specialized and less widespread. It is

Ultrasonic welding is an efficient use

(ABS), poly methyl methacrylate (PMMA),

also known as 'cold welding'because

of energy; almost all of the electrical

because the horn has to resonate at the

polycarbonate (PC) and polystyrene (PS)

energy is converted into vibrations at

correct frequency and withstand high-

can be joined to themselves and in some

the parts are joined below their melting point. It is similar in principle to diffusion

the joint interface, so there is very little

vibration energy. Horns are typically no

cases to one another. Semi-crystalline

bonding, which is aform of brazing (page

heat radiation. It is rapid and there are no

larger than 300 mm (11.81 in.). Longer

312). However, no flux or other surface

other materials added to the joint. There

welds can be made in more than a

thermoplastics such as polyamide (PA), cellulose acetate (CA),polyoxymethylene

preparation is required as long as the

is no risk of contamination, which makes

single step, with multiple heads or as a

(POM),polyethylene terephthalate (PET),

joint fits properly.

this process suitable for food packaging,

continuous process.

polyethylene (PE) and polypropylene (PP)

Horn (tool) size and shape is limited

Joints must be designed with consideration for transmitting sufficient

can only be joined to themselves. There are many factors that affect the

toys and medical products.

COSTS

Welding reduces mixing materials,

Horns have to be made from high-grade

weight and cost by eliminating the need for mechanical fasteners or adhesives.

requires a new horn

Above Ultrasonic welding is a precise and neat Joining

Cycle time is very rapid. Welding time is typically less than 1 second. Loading

which means parts cannot be easily

to be mactiinedfrom

process,ascan be seen

disassembled for recycling. However, if

high-grade aerospace

in this microscopic

and unloading will increase cycle time

only like materials are joined, this is not

aluminium ortitanium.

image of a shear joint.

a problem.

energy to the interface.The tool has

ability of a material to weld to itself or

aerospace aluminium or titanium. Even

to be within a certain distance of the

another plastic. For example, a material

so, tooling costs are generally low.

joint. Generally, amorphous materials

has to be sufficiently stiff to transfer

dampen the vibrations less and so can

vibratory energy to the joint interface.

be far field welded, meaning the joint is

Amorphous materials are more

more than 5 mm (0.2 in.) from the horn

suited to energy directing joint designs,

slightly. Automated and continuous

contact point. However, semi-crystalline

whereas semi-crystalline materials are

operations are very rapid and can

and low stiffness parts have to be near

best welded with shear joints.

produce several welds per second.

This Is a permanent joining method,

Top Each application

Case Study

Ultrasonic welding a shear joint This case study illustrates the equipment

or 40 kHz. This application requires 30 kHz.

used in ultrasonic joining and a simple shear

The converter, booster and horn are screwed

part and the welding process is completed

joint in a small impellor.

together and inserted in a vertical pillar

in less than a second (image 6).The finished

assembly (images 2 and 3).

part is removed from the anvil with a

This product is suitable for ultrasonic joining because a shear joint is used, housed in the lower part. This provides a clean finish

The parts that are going to be joined

permanent hermetic joint (image 7).

(image 4) make up a small impellor. There

with very little flash. It is a 3-dimensional

is a small step on the blades of the impellor,

shape, but tooling is made for every

which provide the interference for the shear

application, so this does not increase costs.

joint. The lower part is placed in the anvil,

Boosters are anodized aluminium and

The horn is brought into contact with the

which provides support (image 5). The upper

coloured to indicate the frequency at which

part, which is over-molded onto a metal bar,

they operate (image 1), which is 15,20,30

locates on top and is self-aligning.

Branson Ultrasonics www.branson-plasticsjoin.com

TECHNICAL DESCRIPTION

Projection Welding Process

In projection welding, the weld zone is localized. This can be done in 2 ways; either projections are embossed onto 1 side of the joint, or a metal insert is used.

Electrode (+] j

This process is capable of producing

Joining Technology

Resistance Welding

multiple welds simultaneously because

unlike spot welding the voltage is directed by the projection or insert. The electrodes

These are rapid techniques used to form welds between 2 sheets

do not determine the size and shape of the

INTRODUCTION

weld. Therefore, they can have large surface

All of the resistance welding techniques

of metal. Spot and projection welding are used for assembly operations, and seam welding is used to produce a series of

are based on the same principle: a high

area that will not wear as rapidly as spot Electrode (-)

welding electrodes.

voltage current is passed through 2 Stage 1: Load

sheets of metal, causing them to melt

overlapping weld nuggets to form a hermetic seal.

Stage 2; Clamp and weld

Stage 3: Unload

and fuse together. As the name suggests, these processes rely on metal's resistance to conducting

Costs • Low tooling costs, if any • Low unit costs

Typical Applications • Automotive • Furniture and appliances • Prototypes

^ Quality Related Processes

Suitability

electricity. High voltage, concentrated

• One-off to mass production

between 2 electrodes, causes the metal to heat and plasticize. Pressure applied during operation causes the melt zone to

Speed

coalesce and subsequently form a weld. The 3 main resistance welding

h • High shear strength, low peel strength 'Arc welding I • Hermetic joints possible with seam • Friction welding I welding • Riveting

• Rapid cycle time

processes are projection, spot and seam.

These are used in many sheet metal

Above Left The ring is placed onto a

industries, but most importantly in

lower electrode, which

automotive construction,They have

locates it to ensure

repeatable joints.

been fundamental in the development

It is clamped into the upper electrode.

Right Projection welding takes a second or so.

of mass produced cars: operating at high

Above

Both welds are formed

speeds they are suitable for both manual

The second part has protrusions that

simultaneously and are

and automated application. A single car

localize the voltage.

full strength almost immediately.

may have up to 4,000 spot welds holding its metalwork together.

Spot and projection welded products include car chassis and bodywork,

TYPICAL APPLICATIONS

appliance housing, electronic circuitry,

Applications are widespread, including

mesh and wire assembly.

the automotive, construction,furniture,

Seam welding is used on products

appliance and consumer electronic

such as radiators, gas and water tanks,

industries.These processes are used for

cans, drums and fuel tanks.

prototypes as well as mass production.

TECHNICAL DESCRIPTION

Spot Welding Process

TECHNICAL DESCRIPTION

Seam Welding Process

Spot welding is the most versatile of the

Seam welding is a continuous process in

resistance welding processes. The weld zone

which the welding occurs between rolling

is concentrated between 2 electrodes that Electrode (+) .

I f I

i

1

!

i

j

®

joints in sheet metal using this technique.

Electrode (+]

joint. Very high voltage plasticizes the metal

1}

I

electrodes. It is possible to form hermetic

c?=C>

are clamped onto the surface of the metal

An alternative technique is used to apply multiple spot welds in a line. This is done

and pressure is applied, forcing it to coalesce

1

and subsequently form a weld nugget.

by replacing the rolling electrodes with

i Because the weld is concentrated

wheels that have a single electrode on the

between the electrodes only 1 weld can

perimeter, which produces a spot weld when

be produced with each operation. Multiple

the upper and lower electrodes are aligned.

This technique is used for high volume

welds are produced in sequence.

Electrode I-) i BB BH Stage 1: Load

Stage 2: Clamp and weld

Stage 3; Unload

Electrode (¦

Equipment is generally not dedicated,

production of metal radiators, for example.

so this process is the least expensive and

the most suitable for prototyping and low volume sheet metal work.

QUALITY

vertical axis, so weld points must be

ENVIRONMENTAL IMPACTS

Weld quality is consistently high. Joints

accessible from above and below. Even so,

No consumables (such as flux,filler or

have high shear strength, but peel

it is possible to weld in confined spaces

shielding gas) are required for most

strength can be limited with small and

with offset or double bent electrodes,

resistance welding processes. Water

localized weld nuggets,

is sometimes used to cool the copper

COMPATIBLE MATERIALS

electrodes, but this is usually recycled

DESIGN OPPORTUNITIES

Most metals can bejoined by resistance

continuously without waste.

These are simple and versatile processes.

welding, including carbon steels,

Above

Spot welding is widely available for

stainless steels, nickels, aluminium,

steel mesh with a hand

Heavy duty handheld welding guns like this

process itself, and spot welding does not

prototyping sheet metal work; it is

titanium and copper alloys,

require any preparatory or secondary

held welder and larger,

are used for general

relatively inexpensive and can be used on

static lower electrode.

sheet metal assembly

a range of materials,

Lett Spot welding stainless

work. Sophisticated

Dissimilarmetals can bejoined

operations that create waste.

COSTS Tooling costs are not always a

Below lett

computer-guided

The welded mesh covers

robotic systems are

together, although the strength of the

consideration: many joints can be welded

a paper pulp molding tool (page 202).

used for high volume

joint may be compromised. Also, different

with inexpensive standard tooling.

welding operations.

thickness of material can bejoined

Specially designed tooling maybe

together, or multiple sheet materials

required to weld contoured surfaces, but

RELATED PROCESSES

laid on top of each other. Assemblies up

is generally small and not expensive.

Resistance welding stands alone in

to 10 mm (0.4 in.) deep can bejoined

the welding techniques: it is simple,

with a single spot weld, but thickness is

standardelectrodes (tooling),which

consistent, low cost and de-skilled. Arc

generally limited to between 0.5 mm and

minimizes costs. However, certain

welding (page 282) and power beam

5 mm (0.02-0,2 in.).

applications, including contoured

welding (page 288) require ahigh level of skill to operate with such efficiency. Formed and riveted joints require

Most assemblies can be welded with

surfaces, require dedicated electrodes.

DESIGN CONSIDERATIONS

Cycle time is rapid. Spot welding can

The position of the weld is limited

only produce 1 weld at atime and so islimitedtoabouti weldpersecond.

preparation. Resistance welding can

by 2 factors;the reach of the welding

be applied with very little surface

equipment and the shape of the

Projection welding can produce multiple

preparation. Weld nuggets are formed

electrode. Theform of atypical handheld

welds simultaneously, so is more rapid.

easily in most metals, regardless of

spot welding gun (see image, opposite,

The speed is affected by changes in

theirhardness. Slightly higher clamping

above) makes clear the constraints.

material thickness, welding through

pressures are required when welding

The weld point must be accessible

harder materials to achieve the same

from the edge of the sheet. Welding

level of coalescence.

equipment typically operates on a

There is no waste generated by the

coatings and variability in part fit up.

Soldering and Brazing Processes Conduction method

Torch method | Workpiece

J

Joining Technology

Soldering and Brazing

1 Small gap

Workpiece

Both these processes form permanent joints by melting a filler

Stage 1: Assembly

Stage 2: Applying heat and filler material

Capillary action

Stage 1: Assembly

Stage 2: Applying heat and filler material Heating elements

processes is the melting point of the filler materials, which is

Furnace method

TECHNICAL DESCRIPTION

lower for soldering than it is for brazing.

Workpiece

Soldering and brazing is made up of

Conveyor belt

the following main elements; joint preparation, flux, filler material and Costs

Typical Applications

Suitability

heating. These 3 diagrams illustrate

• No tooling costs, but may require jigs • Low unit costs

• Electronics • Jewelry • Kitchenware

• One-off to mass production

the most common methods for heating

DDDDDDD

a joint.

Stage 1: Assembly

There are many different techniques, Quality

Related Processes

Speed

• High strength bond, close to strength of parent material

• Arc welding • Resistance welding

• Rapid cycle time 11-10 minutes de¬ pending on technique and size of joint)

D D D D D D-

Stage 2; Applying heat and filler material

but the basic principle of soldering and brazing is that the workpiece is heated to above the melting point of the filler

INTRODUCTION

There are several techniques that

a process known as 'wave soldering'. In

These processes have been used in

employ different combinations of these

operation, the PCBs are assembled with

metalworking for centuries to join lead

elements to achieve a range of design

all the relevant components, preheated

material. At this point the filler becomes

CONDUCTION HEATING

The filler may be added as a pre-form, or

molten and is drawn into the joint by

Conduction heating is typically carried out

coating, which becomes molten under the

capillary action. The liquid metal filler forms

with a soldering iron. The diagram depicts

intense heat of the flames.

a metallurgical bond with the workpiece to

a through joint, which is common on circuit

create a joint that is as strong as the filler

boards. The alternative is surface mounting.

FURNACE HEATING

material itself.

In this case the filler material, solder, is fed

Both of the previous methods have been

frames in stained glass windows and

opportunities. For example, the filler

and dipped in a tank of flux, followed

into the joint separately as a rod or wire.

based on heating localized areas of the

copper sculptures, for example. More

material is drawn into the joint by

by a tank of solder. The solder wets the

of silver, brass, tin, copper or nickel,

Applying a fine coat of filler and flux to the

workpiece. Furnaces heat up the entire

recently, filler material shave been

capillary action, dipped, or inserted as

unmasked metal connections and forms

or a combination of these. The choice

workpieces prior to assembly is similarly

workpiece to the melting point of the filler

developed that are suitable for joining

a pre-form. Heating methods include

apermanent, conductive joint when it

of filler material is determined by the

effective; on heating, the filler material

material. This process is ideal for making

many metallic and ceramics materials.

induction, furnace and flame. Fluxes

is baked.

workpiece material because they have to be

coalesces to form the joint. On heating, the

multiple joints simultaneously, for mass

The most well known application is

protect the surface of the joint from

metallurgically compatible.

filler material coalesces to form the joint.

production and for materials that are brazed

soldering printed circuit boards (PCBs).

oxidizing. An alternative is to carry

An alternative method for massproducing soldered joins is known as

The filler material is typically an alloy

Fluxes are an essential part of the

in a protective atmosphere such as titanium.

TORCH HEATING

Traditionally, lead-based solders were

out the operation in a vacuum or in

'reflow soldering'. In this case, a paste

process. The type of flux is determined

used for many applications, including

the presence of an inert gas (such as

of solder and flux is screen printed onto

by the filler material. The role of flux is to

The next method of heating is using a gas

PCBs. As a result of the negative

hydrogen brazing).

the part and then baked. The advantage

provide a clean, oxide-free surface, so the

torch, usually oxyacetylene. However,

the flux and filler are screen printed onto the

filler can flow around the joint and form

soldering can be carried out with a cooler

joints. The baking process can take longer

a strong bond. This is also referred to as

burning gas such as propane. As with the

than other methods, but many parts can be

surface 'wetting'.

previous technique, the joint is heated to the

joined simultaneously.

environmental impacts of lead and other heavy metals, tin, silver and copper filler materials are now more commonly used.

The melting temperature of the filler

is that hundreds, or even thousands of

TYPICAL APPLICATIONS These are widely used processes. The most common use of soldering is joining

joints can be coated in a single pass of the squeegee. Soldering is also used a great deal in

Wetting is the coverage achieved by the filler material. It is hindered by surface

desired temperature and the filler material

apply heat using a shaped element, which

electronic components, such as surface,

jewelry, domestic plumbing (hermetic

is known as soldering, which is below

or through hole mounting onto PCBs. It is

seals in copper pipes), silverware and

45o0C (8400F), or brazing, which is above.

ideal for this because solder is conductive

food preparation items, restoration and

But the melting point of the workpiece is always higher than the filler material, so

and is suitable for joining delicate

repair work (re-soldering).

filler materials are non-ferrous.

assembled by hand using a soldering

soldering because the filler material

they are coated with metal by electroplating

may have many torches fixed in place

iron, especially for low volume parts.

has a higher melting point than solder.

(page 364), or vacuum metalizing for non-

and pointing at the workpiece such as in

High volume production is carried out in

Typical applications include industrial

conductive materials (page 372).

the production of certain bicycle frames.

There are 3 main elements to the process: heating, flux and filler material.

Brazing is generally stronger than

Instead of a furnace, it is possible to

is added. A small gap of approximately

material determines whether the process

components. Many electronic parts are

The filler material can be added as a pre¬ form, or as in the case of reflow soldering,

contamination and surface tension between

0.05 mm (0.02 in.) is necessary to facilitate

surrounds the part without touching it, to

the materials. In some instances, such as

capillary action. The gap can be larger, but

elevate the temperature of the joint area.

reflow soldering, fluxes are incorporated

this will affect the strength of the joint.

This technique is more commonly used for

into the filler to aid wetting. To encourage wetting on the surface of ceramic materials

This is not restricted to manual operations. Mass production methods

large volume production brazing.

pipework, bicycle frames, jewelry

out with brass filler, the colour can be

material will bridge the gap.This also

COMPATIBLE MATERIALS

pressure and very thin film of filler

The cycle time for furnace techniques

and watches. Brazing is also usedfor

adjusted to suit the parent material.

mean s very complex and intricate joints

Most metals and ceramics can be

coated onto the joint interface. When

may be longer, but is offset because

can be made because the molten filler is

joined with these techniques. Metals

the temperature is raised a very small

multiple products can be joined

drawn right through.

include aluminium, copper, carbon steel,

amount of pressure is applied, which

simultaneously.

stainless steel, nickel, titanium and metal

causes the molecules in the joint to

matrix composites.

mix and form a strong bond. Dissimilar

joining components in engines, heating elements, and parts for the aerospace

DESIGN OPPORTUNITIES

and power generation industries.

The main advantage of these processes is

Alternatively, the filler material can

that they do not affect the metallurgy of

be inserted into the joint as a pre¬

RELATED PROCESSES

the parent material. Even so, an integral

form. In such cases, it is possible to join

Like arc welding (page 282), brazing

metallurgical bond is made at the

multiple products, or multiple joints

and to metals. Many ceramics can be

uses thermal energy to melt the filler

interface by the molten filler material.

simultaneously.

joined, but brazing is generally reserved

material. But soldering and brazing do

Soldering and brazing are simple

Ceramics can be joined together

materials, such as metals and ceramics,

ENVIRONMENTAL IMPACTS

can be joined in this way.

Soldering and brazing operate at lower temperatures than are welding.There

for engineering materials due to the

COSTS

are very few rejects because faulty parts

sophistication of the process.

There are no tooling costs. But jigs may

can be dismantled and reassembled.

not melt the parent material, which is

processes, but there are many variations,

DESIGN CONSIDERATIONS

beneficial for thin, delicate and sensitive

which make them versatile and

The filler material determines the

components. Resistance welding (page

suitable for many different materials

optimum service temperature and

diffusion bonding, is suitable for joining

However, joints can be designed to locate

308) is used for similar applications but

and joint geometries. The range of

strength of soldered and brazed joints.

ceramic, glass and composite materials.

and therefore do not need to be jigged.

with different joint geometry.

techniques cover manual and automated

Butt, tee and scarf joint types are not

production, making these processes

generally suitable for these processes

QUALITY

equally suitable for one-off and mass

because joint interface must be as

Soldering and brazing do not heat the

production. One-off and small batch

large as possible.Therefore, whatever

joint above the melting temperature

production is typically carried out with

the configuration, the joint interface is

of the parent material and so there is

ahandheldtorchandfillerrod,whereas

designed to provide substantial surface

minimal metallurgical change, or heat-

mass produced items are fed through a

area. This may affect the decorative

affected zone (HAZ). The finish of the

furnace on a conveyor belt.

aspects of the product.

1 '' joint bead is usually satisfactory without

Filler material is drawn into the

the need for significant grinding. And

j oi nt by capill ary acti on. Th erefore, th e

the size of the products is limited by

even though brazing is usually carried

joints do not have to fit exactly; the filler

chamber size.

Case Study

Brazing the Alessi Bombe milk jug This is the Bombe milk jug (image 1). It was

There is very little finishing required.

designed by Carlo Alessi in 1945 and is still in

The brazed part is removed from the jig

production today. It was originally made by

complete (image 5). It is lightly polished

metal spinning brass (page 78), but is now

and cleaned before being packed

deep drawn stainless steel (page 88). Brazing

(image 6).

is used to join the spout and handle even though it would be quicker by resistance welding. Brazing is still used to maintain the integrity of the original design. First of all, the joint is checked and coated with flux paste (image 2). An overlap has been created between the spout and body to maximize the surface area to be joined.

They are mounted into a jig (image 3). The brazing process is very rapid, lasting 30 seconds or so (image 4). The craftsman

first warms up the join area with an oxyacetylene torch. When it is up to temperature, the filler material is added.

It flows into the joint interface and forms an even bead.

In furnace and vacuum methods

Labour costs are generally low.

A similar process to brazing, known as

This process joins materials in a vacuum chamber, using a small amount of

be necessary to support the assembly.

Cycle time is rapid and ranges from i-io minutes for most torch applications.

i/i

o o m

X)

Staking Process

Butt

1

Scarf



¦2 OJ

Hot air staking

Ultrasonic staking

Alternative profiles

°

f

Joining Technology

Staking Thermoplastic studs are heated and formed into permanent joints. This process is suitable for joining dissimilar materials

INTRODUCTION These are dean and efficient processes

used to assemble injection molded

such as plastic to metal. There are 2 main techniques: hot air and

thermoplastic parts with other materials.

ultrasonic staking.

They utilize the ability of thermoplastics to be heated and reformed without any loss of strength.

The joint configurations resemble 1 Low tooling costs Low unit costs

Quality • High strength joints with variable appearance

Typical Applications

Suitability

• Appliances • Automotive • Consumer electronics

• Medium to high volume production

Related Processes Hot plate welding Ultrasonic welding Vibration welding

Speed Rapid cycle time (0.5-15 seconds)

rivets. A plastic stud, injection molded onto the component, is heated and

DESIGN OPPORTUNITIES

formed into a tight fitting joint.

This is a simple process that eliminates

parts (page 50) and so large volumes.

Dissimilar materials can be joined, as

consumables such as screws and rivets.

These joints are usually internal

long as 1 is thermoplastic; staking is used

extensively to join metal circuitry into

The studs are injection molded into the part and add no cost to the

plastic housing.

forming process.

Staking is limited to injection molded

TECHNICAL DESCRIPTION The thermoplastic stud is softened with hot air or ultrasonic vibration. It

and so appearance is not a major

is then formed into a domed, knurled,

consideration. Due to the nature of the

split or hollow head. The shape of the

process joints are neat and clean, but the

tool is adjusted to fit the requirements

finish is not controllable.

of the application and stud diameter.

The largest areas of application are in the

snap fits. The advantage of staking is that multiple fixing points can be

COMPATIBLE MATERIALS

to 5 mm (0.02-0.2 in.). Rectangular

consumer electronics and automotive

molded in, as long as they are in

This process is limited to injection

and hollow studs can be much larger,

industries. In many instances, staking has

the same line of draw (tool action).

molded parts. Suitable materials include

replaced mechanical methods such as

Snap fits are more difficult to integrate

screws and clips.

onto a product's surface without

polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS) and

complextool actions.

poly methyl methacrylate (PMMA).

An alternative to staking is molded

TYPICAL APPLICATIONS

Applications in the automotive industry include control panels,

Round studs are typically 0.5 mm

Multiple studs can be heated and

as long as the wall thickness is thin enough for staking. Hot air staking is a 2 stage process.

In stage 1, hot air is directed at the stud. The temperature of the air is determined by the material's

dashboards and door linings. Staking is

formed simultaneously to form large

COSTS

ideal for joining electrical components

joint areas. It is possible to produce

Tooling costs are low. Aluminium jigs

stake with a profiled head presses

into plastic housing because the studs

watertight seals by sandwiching a

are required to support the part during

down onto the hot stud. This

are insulating.

rubber seal in the assembly.

assembly. Ultrasonic staking uses a horn

simultaneously forms and cools the

(tool). Hot air staking uses standard

stud and joins the materials.

There are no restrictions on the layout,

RELATED PROCESSES

pattern or number of studs. Pressure

tooling, which is laid out to suit the

If 2 similar materials are being joined

is applied during operation and so the

orientation of the studs.

then ultrasonic (page 302), hot plate (page 320), vibration (page 298) or other

joints are tight and free from vibration.

Cycle time is rapid. Ultrasonic staking

Low pressures are sufficient to form

can form joints in 0.5-2 seconds. Hot air

welding techniques can be used. Staking

the joints, so thin walled and delicate

stands alone in its ability to join plastics to metals without additional fixings.

parts that may not be able to stand up to vibration can be joined in this way.

staking cycle times are 5-15 seconds. Labour costs are low because these processes are generally automated.

plasticizing point. In stage 2, a cold

Ultrasonic staking is more rapid and takes only a few seconds. It is a single

stage operation in which the stud is heated up by ultrasonic vibrations. As the stud is heated up It softens and is formed by pressure applied by the tool. Ultrasonic welding is suitable for a range of other operations including

QUALITY

DESIGN CONSIDERATIONS

ENVIRONMENTAL IMPACTS

These are permanent joints.The

The principal consideration is that the

Staking eliminates consumables such as

strength of the jointis determined by the diameter of the stud and mechanical

studs should align in a vertical direction,

rivets, screws and clips.

otherwise they cannot be formed in a

properties of the parent material.

single stroke.

welding, sealing and cutting.

Case Study

Case Study

Hot air staking This case study demonstrates atypical

In this case, ultrasonic staking is used to join

studs (image 3). The ultrasonic vibrations

hot air staking application. The parts

a rubber seal onto an injection molded part.

form the studs very quickly. After a couple of

being assembled are the lamp housing

The 2 parts are assembled on a jig (image 1).

seconds the joint is complete and the horns

The studs are rectangular to provide a larger

retract (image 4).

and electrical contacts.

The lamp housing is placed into a tool and the pressed metal contacts are placed over the studs (images i and 2). A stream of hot air is directed at each stud for a few seconds (image 3). Cold dome-headed tools form the hot plastic studs (image 4).The stakes retract and

joint area. The ultrasonic horns are mounted onto a single booster and work simultaneously. The

inside of the horn forms the stud into the desired shape (image 2). The ultrasonic horns compress onto the

parts and apply vibrations to heat up the

the assembly operation is complete (images 5 and 6).

Featured Manufacturer

Featured Manufacturer Branson Ultrasonics

Branson Ultrasonics

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4

Hot Ptate Welding Axial force applied

Joining Technology

Hot Plate Welding This is a simple and versatile process used to join materials. The joint interface is heated to above its melting point, causing it to plasticize. The parts are then clamped together to form the weld.

INTRODUCTION Hot plate welding is used to form joints in extruded and injection molded (page 50) thermoplastic parts. It is a very simple process: the joint interface is heated until it plasticizes andthen pressed together

Stage 1: Loading

Stage 2; Heating

until it solidifies. It is also a versatile process: size is restricted only by the Costs 1 Moderate tooling costs 1 Low unit costs

Quality High quality homogenous bonds Hermetic seals possible

Typical Applications • Automotive • Packaging • Pharmaceutical

Suitability • Batch to mass production

size of the heating platen, and the joint profile may be flat or 3D.The equipment can be either portable or fixed to a

required to form the joint, unlike these

production line.

delicate parts can be welded.

Related Processes Ultrasonic welding Vibration welding

• Variable cycle time (30 seconds to 10 minutes)

other processes, which means small and

TECHNICAL DESCRIPTION This process is made up of several

and Impractical for complex and

stages, which can be divided into 3 main

undulating joint profiles. PTFE coatings

operations; loading, heating and welding.

start to degrade above 270°C (518°F) and

TYPICAL APPLICATIONS

QUALITY

The automotive Industry is the largest

The strength of the weld Is affected

the tools, which generally operate on a

only be used for low melt temperature

user of hot plate welding.The process

by the design of the part and type of

vertical axis. They are held in place by a

plastics such as polypropylene |PP) and

is also usedfor some packaging and

material. Strength Is therefore very

small vacuum. The tools align the joint

polyethylene (PEl.

pharmaceutical products.

difficult to quantify because it varies according to the application. Flash

Interface, so that it can be heated and

RELATED PROCESSES Similar joint profiles are suitable for

produced by pressure in the welding operation is often left untrimmed. It is

vibration (page 298) andultrasonic (page

posslbleto conceal the joint flash with a

302) welding.This process is selected

flange around the weld area.

because only small levels of pressure are

Heating andplasticizlng is localized, up to i mm (0.04 in.) on either side, and so the process does not affect the structure of the workpiece.

In stage 1, the parts are loaded into

welded very accurately. A pre-heated platen is located between the parts. In stage 2, the parts are brought

into contact with the heated platen,

give off toxic fumes. Therefore, they can

The hot plate Is generally a flat plate of aluminium, but can be profiled to accommodate parts with a 3D joint Interface ias shown In the diagram). In stage 3, the parts separate from the

which raises the temperature of the joint

heated platen, which is withdrawn to allow

interface and plasticizes the outer layers

the parts to be brought together. Axial

of material. The temperature Is adjusted

pressure Is applied and the plastlcized

according to the plastic parts being

joint Interfaces mix to form a homogenous

welded. Generally, it Is set 50°C to 100°C

bond. A pre-determined amount of

(90-180°F) above the melting temperature

material Is displaced by the pressure,

of the polymer because it has to warm the

which produces small beads of flash.

DESIGN OPPORTUNITIES

plastic up enough for it not to fall below

The parts are held In place until

There are few restrictions on part size

melting point before the weld has been

the polymer has solidified and cooled

and geometry; the joint interface can be

made. Maximum temperature is around

sufficiently so that It can be removed.

very complex and have both internal and

500°C (932°F).

Small parts are typically heated for around

external welds.The only requirement

is that it can be accessed by a hot plate

The hot plate Is coated with a thin film

10 seconds and then clamped (welded) for

of polytetrafluoroethylene (PTFE), which

a further 10 seconds. Therefore, cycle time

along one axis. Joints on different axes

prevents the melting plastics from sticking

Is up to 30 seconds. Large applications

must be welded in a second operation.

during heating. For particularly sticky

may take considerably longer.

This process is not specific to any

plastics, heat Is applied without contact

thermoplastics material. In other words,

different materials can be welded with the same tooling. All that need to be adjusted Is the temperature of the heating platen.

(convection rather than conduction), but this can cause problems. The benefit

of contact with the tool Is that pressure can be applied for uniform heating. Non-contact heating Is less effective,

Case Study

¦ Hot plate welding an automotive part This product is a typical application for hot

is withdrawn. The parts are then brought

plate welding. It is part of a water-cooling

together and held under pressure until the

system for an automotive under-the-

joint interface has mixed and solidified

bonnet application. This process is ideal

(image 6). The whole process takes no more

because both internal and external welds

than 25 seconds.

can be made simultaneously. Only a small

amount of pressure is required to form

The tools part and leave the welded product in the bottom half (image 7). The

the weld, which is suitable for thin wall

part is removed and checked. A bead of

sections.

flash is typical with this process (image 8);

The part is made of 2 injection molded halves (image i).The top and bottom half

it builds up around thejoint as the pressure is applied.

are loaded into their respective jigs and are held in place by a small vacuum (linages 2 and 3). The required pressure,

heating and welding time have been established through tests and so the process is run automatically to ensure

accurate repeatability; the operator sets the programme for these particular parts (image 4). Heating takes place on a heated platen (image 5), which raises the temperature of the material to more than 5o0C (9o0F) higher than its melting point.This ensures that there is sufficient heat build up in the joint for welding to take place. After only a few seconds, the

tools separate and the heating platen

DESIGN CONSIDERATIONS

COMPATIBLE MATERIALS

This process is most commonly used to

Most thermoplastics can be joined in this way, although it is limited to injection

10 seconds. However, complex and large

weld butt joints. Lap joints are possible in simple parts and extrusions, but this is a

molded and extruded parts. Some

10 minutes.

much less common configuration.

materials, in eluding polyamide (PA), oxidize when they are heated to melting

orfully automated, so labour costs are

by increasing the surface area of the

point, which can decrease the strength of

relatively low.

weld. Incorporating a tee-shape or right

the weld.

The strength of the joint is improved

The maximum dimension of part

welds can take considerably longer; up to

Hot plate welding is either partially

ENVIRONMENTAL IMPACTS

angle at thejoint interface,for example, will increase the weld area.

Cycle time is generally rapid; around

COSTS

This process does not add any material to

Tooling costs are moderately expensive

thejoint and there is no waste produced

that can be welded is limited by the

because they are required to support the

during welding. Hot plate welding has a

size of equipment, which can be up to

part accurately during welding. Parts are

low environmental impact.

620 mm by 540 mm (24.41 x 21.26 in.) on

often supported with a vacuum, which

the heating pi aten an d up to 350 mm

further increases cost.

(13.78 in.) high.

Joint Configurations

Joining Technology

Joinery

•L

w

Contemporary furniture is constructed with both handmade and machine made joints. There are many different types, and it is up to the joiner to select the strongest and most visually pleasing

¦/ ,

for each application.

Costs

Typical Applications

Suitability

• No tooling costs; jigs may be necessary • Moderate to high unit costs depending on the complexity

• Construction • Furniture and cabinet making • Interiors

• One-off to high volume production

Related Processes

Speed

• Friction welding • Timber frame construction

• Cycle time depends on complexity

Quality

_

|

1 ' '¦]

TECHNICAL DESCRIPTION

INTRODUCTION Joinery remains an essential part of

sympathetic to the strengths and instabilities of this natural material.

construction, especially if the joints are on display. Buttimberframe

The diagram illustrates the most common

these is that they are concealed within the

joint types. They include handmade and

joint interface. These are widely used in high

perpendicular lengths of wood. The leg is the

machine made configurations, which are

volume production and flat pack furniture.

tenon and the mortise the hole. The tenon is

Joints can be seamless and almost

construction tends to be concerned with

used in furniture construction, house

industry have combined over the years

invisible, or they can provide contrast to

speed of operation and reliability of joint.

building and interior structures.

and as a result a standard selection

emphasize the joint.These are decisions

Metal fixtures are often used, rather than

There are U main types of adhesive,

of joint configurations have emerged.

made by the designer and made possible

which are urea polyvinyl acetate (PVA),

These include butt, lap, mitre, housing,

by a skilled joiner.

spending time cutting a complex joint. The advantage of gluing is that it spreads th e 1 oad over the entire joint and

formaldehyde (UF), 2-part epoxies and polyurethane (PUR). PVA and UF resins are

A lap joint increases the size of the

is not visible from outside.

the,least expensive and most widely used.

interface to include gluing to long grain on

PVA is water based and non-toxic, and

both sides. This increases the strength of the

welding (page 294) may compete with

excess can be cleaned with a wet cloth. PUR

joint and requires more preparation.

conventional gluing techniques.

and 2-part epoxies can be used to join wood

furniture and cabinet making. Craft and

mortise and tenon, M-joint, scarf, tongue and groove, comb,finger and dovetail.

TYPICAL APPLICATIONS

Additionally, butt joints are strengthened

Joinery is used in woodworking

with dowels or biscuits.

All of these joints can be further reinforced with screws and nails, but this

section is dedicated to joints that are

industries, including furniture and cabinet making, construction, interiors,

In the future, linear friction

Typical furniture includes tables,

QUALITY

usually cut on a band saw, and the mortise

joining 2 planks at right angles. It is more

on a mortiser, which is a machine with a drill

aesthetically pleasing than a butt joint

bit inside a chisel that cuts square holes in

because it ensures continuity of long grain

wood. Alternatively, the mortise can be cut

and avoids exposed end grain.

by hand. There are many different types

A comb joint (also called a finger joint)

including haunch, shoulder, blind, through (illustrated) and pegged. Scarf joints, tongue and groove, M-joints

and finger joints are primarily used to join planks of wood to make larger boards.

provides a much larger gluing area and is a

They increase the gluing surface between

ceramic, and are waterproof and suitable for

common joint for boxes or drawers in tables

2 planks in a butt joint configuration.

exterior use. They are rigid, so restrict the

and cabinets. It is made by a series of spaced

movement of the joint more than PVA.

cutters on a spindle molder, a spinning

for mass production. They are cut on a high¬

cutter for profiling lengths or ends of wood.

speed spindle molder.

to other materials, such as metal, plastic or

boat building andpatternmaking.

A mitre joint is a simple, neat method of

Mortise and tenon joints are used to join

M-joints are machine-made and suitable

secured only with adhesive. (For metal

chairs, desks, cabinets and shelves.

The quality of joint is very much

fixtures in timber frame construction,

Joinery is used in construction for timber

dependent on skill.There is very

see pages 344-7.)

roof trusses, gable ends, doors and

little room for error, but mistakes are

window frames. Interior applications

because the 2 planks are simply cut to

They are cut with re-entrant angles, which

designed to integrate lengths of timber

length. However, they are also the weakest

increase the strength of the joint In certain

into a continuous profile. It is designed to

because there is a relatively small interface

directions. They are especially useful for

maximize gluing area and joint strength.

for gluing and 1 face is end grain. End grain

drawers, which are repeatedly pulled and pushed from the front.

and decoratively.The art of joinery

for this process include floors, walls,

inevitable. Skilled cabinet makers differentiate themselves by their ability

is using wood to its strengths. It is

structures and stairwells.

to repair mistakes imperceptibly.

Joints have to work both functionally

Products made from wood have

ani sotropi c an d i s stron g er al on g th e

Butt joints are the simplest form of joinery. They are inexpensive to prepare

length of its grain. It is alsoproneto

RELATED PROCESSES

unique characteristics associated

is the least strong face for all fixing types,

shrinking or expanding as it dries or

Joinery and timber frame structures

with visual patterns (growth rings),

including adhesives, nails and screws.

(page 344) overlap. Simple joinery

smell, touch, sound and warmth. High

absorbs water from the atmosphere. Therefore, the joint design must be

is used a great deal in timber frame

quality woodwork is often left exposed.

Butt joints are reinforced with dowels, biscuits or metal fixings. The benefit of

Dovetail joints are modified finger joints.

A housing joint is a lap joint in the middle

The finger joint is machine-made and

There are many variations on each of

the above joints, including the angle of interception and whether the joint detail

of a workpiece. It is common for shelves and

penetrates right through the wood or is blind

cabinet making.

(not right through).

Case Study v.

Mortise and tenon and M-joints in the Home Table This is the Home Dining Table, which was designed by BarberOsgerby in 2000. It is

On the assembled table the mitre joint is almost invisible (image 7). The grain merges

on the front of the leg because the 2 halves of the leg are cut from the same plank of wood.

produced from solid oak with a range of different joints (image 1). The legs are mitred together (image 2). The legs and table frame are joined with a mortise and tenon, the traditional

and strongest joint for this application (images 3-5). The top is made by joining solid planks of oak with M-joints (images 6 and 7).

Materials like medium density fibreboard

using butt joints will be less expensive

(MDF) tend to be concealed under several

than finger or dovetail types. However,

layers of paint. A very high level offinish

glued butt joints may not provide such

can be achieved on these surfaces with

a large and strong joint interface as other methods.Therefore, very strong

repeated painting and polishing.

adhesives, dowels and biscuits are used

DESIGN OPPORTUNITIES

to maximize strength.

Joints have several primary functions, For example, the framework and legs

one-third the thickness of the workpiece.

COMPATIBLE MATERIALS

change of grain direction and joining

of a table are join ed together, partly

This will ensure that there is sufficient

The most suitable woodfor joinery is

shapes that cannot be made in a single

because the grain should run in different

material aroundthe joint to support it.

process orfrom a single piece.

directions for optimum strength.The

which include lengthening or widening,

The style of joint should minimize the

The choice of joint is determined

solid timbers, including oak, ash, beech, pine, maple, walnut and birch. Joinery is not limited to wood. These

most common joint forthis application is

by a balance between functional and

amount that wood will naturally twist

a mortise and tenon because it helps to

decorative requirements, and economic

methods can be applied to any material

and buckle, reduce weight and maximize

prevent twisting.

factors.There are types of joint that

as long as it is sufficiently hard to cut a

have been used traditionally for joining

joint into. Synthetic materials will not

gluing area.

Joinery is often combined with CNC

6

legs to tables and panels to doorframes

require such complex profiles because

of designing with timber. It is possible

machining (page 182), laminating (page 190), steam bending (page 198), timber

or making shelves and drawers, for

they are more stable than wood.

to make large flat surfaces, such as

frame construction and upholstery (page

example. For each application the joints

tabletops, of planks joined together

338).The joints maybe exposed and

are modified and adjusted.The case

COSTS

with M-joints or tongue and grooves

decorative or purely functional.

studies illustrate some of the most

Most applications do not require tooling.

ENVIRONMENTAL IMPACTS

common joint types and how they

Some machine made joints may need

Wood has many environmental benefits,

are used.

tool s cut for spindle molders or routers,

especially if it is sourcedfrom renewable

but these are generally inexpensive.

forests.Timber Is biodegradable, can be

Cycle time 1s totally dependent on the complexity of the job and the skill

reused or recycled and does not cause

Joinery maximizes the opportunities

and with 'bread board'ends of wood fixed across the ends of the planks to

DESIGN CONSIDERATIONS

prevent warping. Long and continuous

There is no limit on the size of plank

lengths can be made with M-joints and

orlength of wood that can be joined.

exposed joints. For example, a mitred

finger joints. Shelving and cabinets can

However, the type of joint and its size

be assembled with simple housing, lap

relative to the wood are important

joint will cover up end grain and provide a neat edge detail with continuity of

Aesthetics play an important role for

Labour costs tend to be quite high due to the level of skill required.

of the operator. A single joint may take

any pollution. Joints tend to be formed by cutting, so

or butt joints reinforced with dowels

considerations.There are guidelines

surface grain, whereas comb and dovetail

only 5 minutes to cut and assemble, but

or biscuits. Simple boxes can be made

to maximize retained strength in the

joints express craftsmanship and add

there might be 15 different joints on the

wood chips are often burnt to reclaim

with butt, mitred and lap joints, or more

timber that is cut to form the joint.

perceived value.

product. Generally, the same or similar

energy in the form of heating.

decorative comb and dovetail joints. Change of grain direction is especially useful for load bearing applications.

For example, mortises (mortise and tenon joint) and grooves (tongue and

groove joint) should be no wider than

Economic factors, such as cycle time and labour costs, often have a role to play. For example, a part that is being made

joints will be used as much as possible on a product to minimize set up and changeover time on the machines.

waste is unavoidable. Dust, shavings and

Featured Manufacturer Isokon Plus www.isokonplos.com

Case Study

Case Study

Mitred and biscuit reinforced butt joints in a bedside table

Dowelled butt joints in a table drawer

This is a simple, veneered bedside table.

This case study illustrates dowels used to

The 4 sides of the product are lipped with

strengthen butt joint configurations. The

solid oak edges, veneered, cut to size and

parts are drilled with the holes set apart to

materials (image 2).They are inserted into

mitred. Grooves are cut for the biscuit

exact measurements (image i).This is often

the joint with glue and hammered into

carried out on a drill with 2 heads, which are

place (image 3).

reinforced butt joints. To join the mitred joints, the parts are laid face up (joint down) on the table. The

The dowels are made from beech or birch, because they are suitably hard

set exactly the same distance apart for both sides of the joint.

faces are taped (irnage i) to keep the joint tight during assembly Prior to assembly, the biscuits (Image 2) are placed into precut grooves on the butt joint, and glue is applied to all of the joints (image 3). The 4 sides are assembled with the tape still in place (image 4).This keeps the joint tight and acts like a clamp (image 5).

Featured Manufacturer

Windmill Furniture www.windmilLfurniture.com

Featured Manufacturer

Windmill Furniture www.windmiUfurniture.com

Case Study

Case Study

Comb jointed tray

Decorative inlay

Comb joints are traditionally used to

This is a simple form of wood inlay,

join the sides of trays and drawers. The

used visually to separate 2 veneers on a

joint is cut by spindle molder with a set

tabletop (image 1). The inner veneer is

of cutters separated by matched spacers.

bird's eye maple and the outer veneer is

Both sides are cut with the same set up to

plain maple. This type of decorative Inlay

ensure a perfect fit (image i), which can

is made up of layers of exotic hardwoods

be assembled by hand (image 2).

and fruitwoods, which are cut Into strips

The base of the tray, which is located

(image 2). The groove is cut by router, and

in a housing joint between the 4 sides,

the strips of inlay are bonded In with UF

holds it all square, and the finished

adhesive (image 3).

product is lacquered (image 3).

Featured Manufacturer

Windmill Furniture www.windmillfurniture.com

;ase Study

Housing joints in the Donkey This version of the Donkey was designed by Egon Riss in 1939. It is made from birch plywood (image 1). Housing joints are a simple and a strong way to fix the shelves into the end caps (image 2). This use of this joint means that the product can be assembled and glued in a single operation. The end caps are clamped

together, which applies even pressure to all the joints.

Featured Manufacturer

Featured Manufacturer

Isokon Plus

Windmill Furniture

www.isokonplu5.com

www.windmillfurniture.com

Joining Technology

Weaving Weaving is the process of passing strands or strips of material over and under each other to form an intertwined structure. Fibre strength and alignment can be adjusted specifically for each application, reducing weight and material consumption.

Costs • There are no tooling costs • Low unit costs, but dependent on the raw material

Typical Applications • Furniture • Interiors • Storage

INTRODUCTION

Machine made textiles are woven

Weaving is used across a wide range

as panels, which are then secured to a

of industries, including textiles, rug

structural framework.To make 3D profiles

making, sail making and architecture.

they are draped over molds and coated in

This section focuses on rigid textiles,

adhesive to retain their shape.

which are used in the construction and

Hand weaving techniques date back

upholstery of furniture, baskets, fences,

thousands ofyears and are very similar

screens and mats. Rigid textiles can be

today because many are not suitable

Suitability

made not only as flat panels, but also as

for mechanized mass-production.

• One-off to high volume production

3D, self-supporting structures.

There are 3 main types of rigid textile

Quality

Related Processes

Speed

• Depends on raw material

• Steam bending • Upholstery • Wood laminating

• Machine weaving is rapid • Hand weaving is moderate to slow, but depends on size and complexity of part

Nevertheless, there is a substantial market for hand woven products, which

weaving: plain (see image, opposite,

are made in large quantities in countries

above middle), twill (see image, opposite, top) and satin (in which either the warp

with enough labour to make production

or the weft bridges 5 perpendicular

economically attractive. Hand weaving is carried out either

strands or more). Satin has a slightly less

on a loom (in which case it can be

stable textile, a warp- or weft-rich surface

mechanized), between rigid elements

and a more densely packed weave. Other

(which do not have to be parallel as they

types of weaving, such as machine-made

are in machine weaving), or as a 3D self-

tri-axial 'strand caning' (see image,

supporting structure.There are many

opposite, above) and 'basket weaving'

techniques including plaiting (general

(see image,below), are combinations of

weaving), hand caning, lashing, splint

these techniques.

seat weaving and coiling.

TYPICAL APPLICATIONS Weaving is used in many different

Top

Above

areas of furniture construction. Typical

Twill, or herringbone,

Cane weave.This is the

products include stools, chairs, tables,

is a diagonal pattern created by overlapping

of caning, based on

sofas, beds, lights, storage boxes, blinds and screens.

2 strands ormore at a time.

Other products using similar techniques and materials include

Above middle

Above The Lloyd Loom Nemo chair, designed by Studio Dillon in 1998, is made up of a single

most popular method the traditional 7-step manual technique

steam bent ring, onto

to form an octagonal

which the woven

pattern

material is fixed.

Plain weave is a simple

baskets, fences and wall and floor panels.

'1 up, 1 down'pattern.

RELATED PROCESSES

CNC machined (page 182) wooden

advantage is that woven structures can

Alternatives to rigid textiles in furniture

support structure.

be shaped, for example onto a mold in

include upholstery (page 338) with

Wood and composite laminates

leather or'soft'textiles, wood laminating

rely on adhesives to hold the layers

(page 190) and composite laminating (page 206). Similar to upholstery,

together. By contrast, woven materials are maintained by friction.This means

the case of the Lloyd Loom Nemo (see image, above right).

QUALITY

woven 'rigid' textiles are often fixed

woven structures tend to be more

The quality of weave is determined

wonto a steam bent (page 198) or

flexible and deform permanently.The

by the combination of rawmaterial

Loom Weaving Process

Case Study

t #

Weaving upholstery This case study demonstrates weaving and

The metal is concealed in paper (image 4) and

The woven material is transferred onto a

the subsequent upholstery of woven material

is the structural element of the basket weave.

steam bent structural framework (image 8).

onto a steam bent wooden structure. The

Each of the looms is loaded with 664

The edge is stapled with a braid of twisted

example being made is the Lloyd Loom

bobbins of twisted paper warp (image 5). The

paper to secure the strands and prevent any

Burghley chair (image 1).

looms produce flat and continuous woven

fraying (image 9). Finally, the completed chair

material 2 m (6.6 ft) wide (image 6). The wire

is sprayed with a protective coating, which

based weaving material. The warp is made by

wefts are folded along the edge to lock the

ensures the longevity of the material.

twisting strips of Kraft paper into tight fibres

warps in place (image 7). Otherwise they

(images 2 and 3). It is coated with a small

would spread out and fall off the end of the

amount of adhesive to lock it in place. The

structural wefts.

Lloyd Loom manufacture their own paper-

weft has a metal filament along its centre.

TECHNICAL DESCRIPTION Weaving rigid textiles on a loom consists

are separated into 2 sets, which creates a

of 3 movements repeated many times;

basket weave pattern.

raising and lowering the heddle bars, feeding the weft and beating. Each strand of warp is fed through

A weft is fed into the space between the fibres and in front of the beater. The beater is a series of blunt blades that sit between

an eyelet in the heddle bar. The heddle

each fibre. They are used to 'beat' each

bars are operated individually or as a set,

weft tightly into the overlapping warp.

and are computer-guided or moved by

The weft is held in place by the beater

depressing a foot pedal. Moving them up

while the lower heddle bar moves up and

and down determines whether the warp or

the upper heddle bar moves down, which

weft will be visible from the top side. This

locks the weft between the warps. The

is how patterns are made, and they can be

process is repeated to form the next run.

very intricate. In the diagram the heddles

to drop without a parachute, saving valuable materials. Colours and patterns can be woven into rigid textiles. Like 'soft'textiles, they are treated as repeating modules. Alternatively, they can be printed on, or dyed in a solid colour.

Different types and thickness of material are combined to produce and pattern. Nearly all contemporary

DESIGN OPPORTUNITIES

structures with specific load-bearing

weaving is carried out on computer-

Woven structures tend to be

capabilities. For example, the weft can

controlled looms, which produce high

multifunctional, and there are

bind a structural warp together, as in the

quality, repeatable materials. The quality

many opportunities associated with

Lloyd Loom basket weave.

of handmade weaves depends on the

construction and application.

skill of the weaver.

Rigid textiles tend not to be as tightly

Each type of weave has a different

Handmade weaves illustrate a

major advantage, which is that a

appearance, drape and robustness.

woven structure can be designed and

woven as 'soft'textiles. Material is used

Combined with different materials,

constructed to suit a specific load

only where necessary and there is give

an endless number of structural

bearing application.

between the fibres, which makes them

properties can be achieved,This

lightweight and durable structures.They

makes woven structures suitable for

are breathable, which is advantageous

both self-supporting and reinforced

product. Laminated composites,filament

for applications such as beds and chairs,

applications. For example,food parcels

especially in hot and humid climates.

dropped in World War 11 were made by

winding (page 222) and 3D thermal lamination (page 228) exploit this

placing i woven basket inside another

property to huge advantages with 'soft'

for protection: this was durable enough

The continuity and direction of fibres directly affect the strength of a woven

fibres reinforced with rigid adhesive.

Featured Manufacturer

Lloyd Loom www.lloydloom.com

The benefits of weaving 'rigid textiles'

Case Study

according to strength requirements are weight reduction and an aesthetic that is

Strand caning

directly related to function.

The S32 was designed by Marcel Breuer and

formed. The seat back, which is the product

which applies even pressure (image 7) and

DESIGN CONSIDERATIONS

production at Thonet began in 1929 (image 1).

being made here, is steam bent and a groove

the finished seat backs are stacked ready

Hand weaving techniques, which

It is among most highly mass-produced

is cut around the front Into which the cane

for assembly onto the tubular metal frame

tubular steel chairs in history.

is fixed.

(image 8).

include rattan and wicker furniture, are time consuming and labour intensive.

The sheets of strand cane are pre-woven

The cane is hammered into the groove

Machine made weaves tend to be a

on a loom (image 2).There are many different

using a specially shaped tool (image 3).

standard pattern. Even so, there Is a wide

types and patterns, but this octagonal pattern

A spline of cane is then pressed into the

range to choose from.They are supplied

is the most popular. It is a reproduction of the

groove to secure the weave (image 4). They

as a fl at p an el. Th i s can be bent, but

traditional y-step hand caning technique.

are both locked in place with adhesive.

First of all the cane is cut into strips and

typically only tightly in i direction, or gently over a shaped mold. Forcing it into

complex profiles will push the fibres out of alignment and affect the strength and

The excess material is trimmed off and

soaked for at least 35 minutes. This is to

the spline finished off (images 5 and 6).

ensure that it is sufficiently pliable to be

The assembly is placed into a warm press,

aesthetics of the product.

The size of bend is determined by the type of material. Some materials, such as cane, can be bent to very tight angles.

Other materials arenotso pliable and may split.These shapes have to be woven

into a 3D shape by hand, or by joining panels of material.

Many of the materials used in rigid weaving are natural and so need to be protected from the elements. This is often done with a clear or coloured spray

coating (page 350).

COMPATIBLE MATERIALS Woven furniture was traditionally handmade using natural fibres such as rattan, willow and bamboo. Mass production methods can also produce

ENVIRONMENTAL IMPACTS

continuous woven materials from metal,

This process creates products with

paper, plastic and wood.

minimal materials. Hand weaving

methods traditionally use locally grown

COSTS

materials and so do not require the

There are no tooling costs unless the

transportation of raw materials over

weave is formed over a mold. Even then

large distances. However, these practices

the tooling costs tend to be low.

are becoming less common.

Cycle time depends bn size, shape

The mechanical join is formed by

andthecomplexityofthewe ave or 3 D

intertwining materials.Therefore, there

product.

are no chemicals, toxins or other hazards

Labour costs tend to be high because

ahigh level of skill is required. Weaves made by machine and then upholstered onto products require less labour, but still require highly trained operators.

associated with melting, fusing, or

otherwise altering materials to join and Featured Manufacturer

shape them.

Thonet

Most waste is either biodegradable or

www.thonet.com

capable of being recycled.

r

Machine Stitching Process Scarf

CD

t

Tee

1

Overlap Presser fool

Needle 1

Needle bar

Joining Technology

Upper thread

Upholstery

Layered textile or leather

Upholstery is a highly skilled process and the quality of Feed dog

craftsmanship can set products apart. It is the process of

Lower thread

Shuttle hook

bringing together the hard and soft components of a piece of

Bobbin

furniture to form the finished article. Stage 1: Pick-up Stage 2: Loop Stage 3; Finish

TECHNICAL DESCRIPTION

\ • \ Quality

I

• Very high quality that depends on the skill of the upholsterer and type of material

Related Processes • Steam bending • Weaving • Wood lamination

Speed • Moderate to long cycle time depending on size and complexity of product

\

\

^ X ^ \ \ ^

Machine stitching is a simple form of

The needle pierces the layers of material

mechanical joining that requires a complex

and stops momentarily. In stage 2, a spinning

process of making stitches from a single

series of operations to execute. There are

shuttle hook picks up the upper thread.

thread. The downfall of this method is that

3 main types of machine sewing: lockstitch,

The shuttle hook loops behind the lower

if the thread is broken at any point it readily

chain stitch and overlock. The diagram

thread, which is held under tension on the

comes apart.

illustrates lockstitching, which is used to

bobbin. In stage 3, as the shuttle continues

join the leather cover in the Boss Eye chair

to rotate, tension is applied to the upper

of finishing the edge of fabric with multiple

thread, which pulls it tight, forming the next

threads. It protects the fabric from fraying

case study.

INTRODUCTION Atypical upholstered chair consists of

Nowadays, the padding is polyurethane (PUR) foam. It is either

a structural frame, foam padding and a

molded using the RIM process (page 64)

textile cover. Sofas and lounge chairs may

or cut and glued tog ether. Modern foams

RELATED PROCESSES

also have a sprung seat deck. Springs are

have reduced the need for sprung seat

There are many processes used in the

mounted onto the frame or suspended

decks, and many contemporary sofas and

upholstery procedure. Wooden frames

within it.There are 3 main spring

lounge chairs no longer have springs.

tend to be laminated (page 190), steam

systems: 8-way hand-tied, drop-in and

Instead, foam density is designed to

sinuous springs.

provide maximum comfort.

Hand-tied springs are the most

The covering is fabric or leather and

seats and interiors, break out seating and padded walls.

by casting a net of interlocking stitches over

process. The needle and shuttle hook are

forward, catches the fabric and pulls it into

the edge.

synchronized by a series of gears and shafts,

place for the next drop of the needle. The

powered by an electric motor.

fabric is supported between the presser foot

In stage 1, the upper thread is carried

and feed dog. Industrial sewing machines

through the fabric by the needle, and

can repeat this sequence over 5,000 times

the lower thread is wound on a bobbin.

every minute.

bent (page 198) or CNC machined (page 182). Metal frames are bent (page 98) or cut and welded (page 308).The cover is

QUALITY

Right With a highly skilled

The look of the upholstery is largely

expensive and considered superior. Using

is permanently fixed to the padding and

cut out on a CNC x- andy-axis cutter, or

underlying framework.

by hand, sewn together and glued and

dependent on the skill of the upholsterer.

stapled onto the foam and framework.

The comfort is determined by the quality

accurately placed stitches per minute.

TYPICAL APPLICATIONS

The foam padding is either molded

Upholstery is used extensively in

over the framework, or cut and glued

of foam and springs, while the longevity of the product is affected by the rigidity

furniture and interior design. It is

onto it. The choice of RIM is not solely

and strength of the framework.

used to make 'soft'furnishings for the

dependent on quantities because certain

names suggest: drop-in springs are

automotive,marine, home, office and

shapes cannot be produced feasibly in

DESIGN OPPORTUNITIES

a prefabricated unit fixed into the

transport industries.The materials

any oth er way an d h ave to be m ol ded.

The density and hardness of foam can be

framework, and sinuous springs are

for each of these applications will

continuous lengths of steel wire bent

vary according to the likely wear and

mesh stretched over the framework,

or leather cover is adhesive-bonded to

into's' shapes and fixed at either end.

environmental conditions.

wooden, plastic or metal slats, injection

the foam, so undercuts and overhangs

stretched across it and the springs are hand-tied to the webbing up to 8 times. Drop-in and sinuous springs are machine-made.They are as their

The structural framework is generally

Typically, upholstered products

fabricated in wood or metal. Its strength

include lounge chairs, sofas, task and

determines the durability of the product.

office chairs, car seats and interiors, boat

Alternatives to upholstery include

Overlocking, or serging, is the process

stitch. Meanwhile, the feed dog progresses

Lockstitching is a mechanized

them increases cycle time considerably. A wooden box is fabricated, webbing is

Chain stitching, or loop stitching, is the

chosen to suit the application. The fabric

molding (page 50), weaving (page 332)

can be upholstered. Shape limitation

and wood lamination.

is determined by what can be cut and shaped in the textile; single axis curves

operator, an industrial sewing machine can produce over 5,000

Left The distinctive relief pattern of this button tufted Chesterfield

reduced due to increased buying power.

leather sofa is created

Labour costs tend to be high due to the

by pinning the leather cover to the support

level of skill required.

Batch production does not reduce the labour costs,but material costs may be

Upholstering with cut foam These images illustrate a technique for

This case study shows upholstering the

upholstering foam-padded chairs. An

Neo chair using the cut foam technique.

ENVIRONMENTAL IMPACTS

example of a chair produced in this way

The structure is laminated wood (image 2),

Upholstery is the culmination of

is the Sona chair, designed by Paul Brooks

onto which the foam is bonded (images 3

many processes and as a consequence

(image 1). Production began in 2005.This

and 4). The covering material is stretched over the foam and stapled onto the plywood

structure.

Fabrics come on rolls that are typically

Case Study

multiple axis curves require elastic

1.37 m (4.5 ft) wide. Leather comes in

a typical sofa will include many different materials that have varying

technique is suited to geometries that have a constant wall thickness; RIM is more

substrate. Each panel Is made up in this

material or 2 or more pieces of material

various sizes: for example, cow hides

environmental implications.

cost effective for complex and undulating

way and then fitted together to conceal the

stitched together.

range from 4 m2 to 5 m2 (43-54 ft2) and

shapes such as the Eye chair.

inner workings of the chair.

sheep skins can range from 0.75 m2 to

The choice of covering material will affect the environmental impact of

1 m2 (8-10 ft2).

the product. For example, the William

are easily covered with textile, whereas

Each product has to be upholstered individually and so manufacturers are often prepared to run single colours,

The choice of covering material is an

McDonough collection of fabrics

or short runs of colour. The textiles

important factor in determining the unit

available are as varied as the clothes you

price. High value materials, such as high

and manufactured in a closed loop

wear. Different weaves and materials

quality leather from a top supplier like

industrial process. Many leather

have varying levels of durability, andthe

Elmo Leather in Sweden, can double the

materials have to go through a series

toughness of the covering is determined

price of the product

of potentially environmentally harmful tanning and dying processes before they

example, a domestic lounge chair may be

COMPATIBLE MATERIALS

can be used in upholstery. By contrast,

used for only 3 or 4 hours on an average

The area of application, such as

Elmo Leather produce a chrome-free

day, whereas break out areas in offices

automotive, marine, domestic, office,

leather called Elmosoft.There are no

will see much heavier usage.

education, healthcare or public

hazardous substances used in the

Fabrics have varying levels of elasticity and bias. Slightly elastic fabrics reduce

transport, determines the specification

production process.

by the application of the product. For

the number of pieces required to cover

of uphol stery m ateri al. Contract grade materials suitable

produced by Designtex is biodegradable

upholstering with leather,! reason why

for high wear applications include

used on convex shapes because they will

polyamide (PA) nylon, thermosetting

shapes can be nested very efficiently on

bridge concave profiles.

and thermoplastic polyester, synthetic

fabric, producing only 5% waste, whereas

leather polyurethane (TPU), polyvinyl

leathermayhaveimperfectionsthat

it is so much more expensive.The net

in a number of different ways. Possible

chloride (PVC),polyproylene (PP) and

cause up to 20% waste. Offcuts can

details include button tufting, beading

other hardwearing fibres.

sometimes be used in furniture with

and twin stitching.

General upholstery materials for low

o

A lot more waste is produced when

a 3D shape. However, they can only be

Upholstered covers can be finished

c

~D nr

smaller pieces, or gloves.

wear applications include leather, flock,

DESIGN CONSIDERATIONS Whatever the design, it must be possible to cut and stitch a fabric shape that will

raffia, mohair, cotton and canvas.

Outdoor application materials have to withstand exposure to the elements

cover it.There are various techniques

and ultraviolet light. Examples include

used to conceal the open end of the fabric cover. Conventionally, the fabric

synthetic leather TPU and polycarbonate (PC) coated materials.

cover is pulled on and the edges stapled onto a single face, typically the bottom or

COSTS

back of the product. This is then covered

There are no tooling costs in this process,

with a separately uph ol stered pan el.

but there may be tooling costs in the

Concave shapes can be upholstered, but the cover will need to be secured in place with a panel, pins, ties or adhesive to maintain the cover in place.

RIM foam process and for any wood laminating or steam bending.

Cycle time is quite long but depends on the size and complexity of the piece.

Featured Manufacturer Boss Design www.bossclesign.co.uk

Upholstering a RIM foam chair The Eye chair was designed by Jackie Choi for

inside for additional strength. Many different

Boss Design and production began In 2005.

stitch patterns and details can be applied;

process requires a great deal of patience; the

It is covered with fabric or leather (irnage 1).

this is twin stitch. The patterns are carefully

heat from the steam softens and activates the

The polyurethane foam is made by Interfoam using the RIM process. The foam has a metal structure for support and plastic

designed so that the seams line up with the

adhesive, so that as the cover is gently pushed

corners of the chair.

into the desired shape, the adhesive bonds to

Once the leather patterns have been

or wooden panels to which the covering

assembled, the cover is pulled over the

material can be fixed.

foam inside out and sprayed with adhesive

Upholstering this product is a timeconsuming and highly skilled operation. First of all, the foam is coated in a thin film

(image 6). The adhesive is not sticky at this point because it is triggered by steam. The cover is removed and fitted onto the

of adhesive (image 2) and covered in soft

foam (image 7). It is stapled in place using the

polyester or down lining, which helps smooth

plastic panels molded into the product

over imperfections and gives the surface a

for this reason (image 8). Another panel,

better feel (image 3). Meanwhile, the leather is prepared by a pattern cutter (image 4), who carefully has to work out the least wasteful arrangement of

steam and a soft cloth (images 10 and 11). This

upholstered separately, snap fits onto the plastic panel to conceal the trimmed edges (image 9). The leather cover is now securely in

patterns on the sheet. If possible, the patterns

place. However, there are undercuts to

are cut from a single skin and stitched

which the cover must be bonded if it

together (image 5). A tape is sewn on the

is to retain its shape. This is done with

the foam overhang.

The final chair is inspected prior to packing and shipping (image 12).

Fixing Methods

TECHNICAL DESCRIPTION Various fixing methods are used

4

in timber frame construction to

accommodate different joint types and access to them. They are generally

Joining Technology

semi-permanent, and so can be

Timber Frame Structures

removed if necessary.

Nailing is used for tee and overlap joint configurations. It is always

Large-scale timber frame construction uses a variety of fixing methods. Softwood and engineering timber structures can span large gaps. Amongst other applications, they are used for house

preferable to nail through the thinner

INTRODUCTION Timber frame structures are used in

Straight nailing

Skew nailing

Nail plates

factory-made low-rise buildings, interior

advantages. Generally, two-thirds of

structures, roofs, large enclosures and

the nail shank should penetrate the

freestanding structures.There are

building because construction is fast and efficient.

Costs

Typical Applications

Suitability

• No tooling costs • Moderate unit costs, depending on complexity

• Temporary structures • Theatre and film sets • Timber frame housing

• One-off to medium volume production

lower material.

many standard products, including

The strength of a nailed joint is

roof and attic trusses, wall panels and

determined by the angle at which the

floor cassettes. Bespoke structures are

nail intersects the grain because wood

manufactured for each application,

is anisotropic. The nail shank parts the

which m ay h ave different fun ction al

grain as it is forced into the wood. The Bolts

and decorative requirements.

Framing connectors

Related Processes

Speed

• Lightweight and long lasting

• Joinery

• Moderate cycle time (5-30 minutes per frame)

grain contracts around it, forming a

tight grip. Nailing into end grain is the

Engineering timbers utilize the Quality

material and into the thicker material.

This provides obvious mechanical

strength and stability of laminated wood

and exhibitions), permanent and large-

of wood is harnessed and dimensional

weakest, and nailing across the grain

and include plywood, oriented strand

scale structures (including airports,

stability achieved by laminating

is strongest.

board (OSB), laminated strand lumber

government offices and residential

layers with strong adhesives to form

(LSL), parallel strand lumber (PSL) and

housing), and interior structures (such

composite I-beams. These materials

as stairwells, warehouse conversions and

are used in a variety of combinations

wide spanning floors and ceilings).

to produce lightweight structures,

engineering timbers (page 190). Like other natural materials, wood has unique characteristics associated with

visual patterns (growth rings), smell,

Nail plates are effective for tee and butt joints. They are steel plates that have been stamped to form a rack of short nails. Even though these do

not penetrate deep into the material they are strong due to the number

engineered to precise requirements.

RELATED PROCESSES

touch, sound and warmth. The finish can

A variety of softwoods are used, and

Joinery (page 324) and timber frame

be exposed to make use of its sensual

each piece is strength graded. Structural

structures overlap. Joinery tends to use

qualities, or concealed, depending on the

designers select timber strong enough

adhesives and wooden fixtures, whereas

requirements of the application.

preparation. They are not self-tapping,

for each application.

timber frames use metal fixtures for

DESIGN OPPORTUNITIES

pre-hole slightly larger than the shank.

Buildings and other large-scale structures are simulated in CAD

speed and ease of manufacture. There are 2 main housing alternatives

of nails. They eliminate the need for overlapping joints. Bolts tend to require more joint like screws and nails, so require a

There are many reasons for building

However, they tend to be stronger than

software. They are tested for load-bearing

in the UK construction industry, which

with timber: it has a low environmental

other fixing methods because they grip

stren gth an d 1 ocation -specifi c factors

are masonry and steel framework. The

impact, it is lightweight and strong, it

the joint from both sides.

such as wind speed.

choice of material will determine the

is inexpensive and each piece is unique.

method of construction. Timberframe is

It can be shaped using similar processes

to plastic and metal, but will always

As technology in this area progresses,

steadily becoming more popular in the U K due to its beneficial environmental

so does the range of applications.

impact and the speed of production.

APPLICATIONS

Approximately three-quarters of the

retain natural qualities. Timberframe construction is not limited to a range of standard products.

An alternative method for tee

joints in load-bearing applications is framing connectors. These are bent

metal fixings nailed in place to provide support in the critical areas and reduce stress on the joint. They are similar to

a housing joint (see Joinery).

world's housing construction is timber.

QUALITY

Many structural designs have been

Timber frame is the most popular form

Wood is a natural composite made up

refined to give optimum performance,

of construction in countries with cold

of lignin and cellulose.This has many

but this does not limit the designer with

climates because it is such afast and

advantages, but means that designs

regard to size or shape. Manufacturers

efficient method of building.

need to accommodate dimensional

have to accommodate a range of

applications, especially near the coast,

changes as a result of variation in

products, so there is little cost difference

stainless steel fixings should be used

constructed houses, theatre and film sets,

moisture content. In timberframe

between making 10 or 100 identical

to avoid corrosion, which can cause

temporary structures (such as pavilions

construction, the strength and lightness

products using this process.

staining and ultimately joint failure.

Some typical products include factory-

Metal fixtures come in a variety

of finishes. They tend to be made in carbon steel, which is galvanized for improved longevity. For exterior

DESIGN CONSIDERATIONS

Case Study

Designed properly, wooden structures

Constructing a timber frame building

can achieve large spans.They are capable of bearing significant loads, even in

iiii

The load bearing structure of this 4-storey

plates are placed on either side of the joint

rigidity to the framework and maximizes its

be taken to ensure correct support to

timber frame house (image 1) is the

(image 3). Each Joint is placed in a hydraulic

strength without adding too much weight.

reduce stress on load-bearing joints. For

woodwork. It is being clad with a masonry

press, which force the nail plates into the

example, there are guidelines for drilling

skin, which does not come into contact

timber (images 4 and 5). Once the joints are

lightweight I-beams, which are a composite

with the timber framework; there is a cavity

assembled they are pressed simultaneously.

of LVLandOSB (image 10). They can span

between them.

Each piece has been strength tested to verify

distances up to 7.5 m (24.6 ft). They are fully

its structural integrity and thus its location in

assembled in the factory and then dismantled

the framework (image 6).

into units for transportation.

cantilever configurations. Care must

holes, which weaken structures. Wood is anisotropic and is stronger

The structure of the building is

along the length of its grain than across.

manufactured as flat panels off-site in a

It can only be used for load-bearing

factory. The pine struts for the roof and

applications in low-rise construction,

although it is capable of carrying significant load and has been used in the UK for up to 7 storeys.

The wall panels are nailed together using

Floor cassettes are assembled using

The units are brought together on site

attic trusses are cut to length in preparation

pneumatic guns (images 7 and 8). Once again,

and assembled very quickly (image 11). Each

(image 2). They are assembled according to

all of the wood is cut to length and packaged

floor takes approximately 1 day to construct.

the requirements of the drawing, and nail

as a bundle for assembly. The assembly

Framing connectors are used to tie the

process is computer-controlled and

I-beams together (image 12). They are also

adjusts the bed and clamps to fit each

used to tie timber beams into masonry and

on the combination of the frame and

part.The operator and machine work

steel framework.

th e skin. Th erefore, pan el s ten d to be

together nailing the joints.

The strength of timber panels relies

con structe dflatandthenfixedtogether

The strength of these panels is

to form 3D structures.

achieved with a combination of timber

The size of mechanical fixture is

frame and an OSB skin, which is nailed onto 1 side (image 9). The skin contributes

calculated on CAD software to ensure adequate support. Generally, nails are

used for tee and butt joints, while bolts are used for overlapping joints.

COMPATIBLE MATERIALS All timber products Including softwoods, hardwoods, veneers and engineering timbers can be used.

COSTS There are no tooling costs: assembly can

be achieved with hand tools, but the industry is evolving more sophisticated CNC assembly operations. Cycle time is moderate. Each frame takes 3 to 30 minutes to construct. A typical timber frame house can be constructed on site at a rate of a floor per day, but large, complex or curved structures may take longerthan this.

Labour costs are typically high due to the level of skill and number of operators required for large construction.

over competing methods.Timber is a

embodied energy than steel and concrete

renewable material. It has lower levels of

equivalents. Timber is biodegradable,

'embodied energy'than alternatives -in

and it can be reused or recycled.

other words, it uses less energy to grow,

ENVIRONMENTAL IMPACTS

extract, manufacture, transport, install,

One of the main reasons for specifying

use, maintain and dispose of than other

timber frame construction is the

construction methods. In fact, timber

environmental advantage that it has

frame structures have up to 50% less

Finishing Technology

c o 0 U3 '¦P 03

S E

1 Q.

-I

Finishing Technology

Spray Painting Spray painting is a fast and efficient means of applying adhesive, primer, paint, lacquer, oil, sealant, varnish and enamel. The

surface determines the applicable finish and how long the process takes.

INTRODUCTION

propelled onto the surface of the base

Spray coating is the application of liquid

coat. This produces a topcoat that is

borne materials onto a surface.The

multilayered: it is rich with colour near

sprayed material generallyhasi ormore

the basecoat and almost clear on top.

of the following functions: filler, primer,

This promotes a glossy, rich and intense

colour, decoration and protection.

colour finish.

High gloss, intense and colourful

finishes are produced by a combination

The majority of spray painting is manually operated. However, there

Costs

Typical Applications

Suitability

of meticulous surface preparation,

are sufficiently high volumes in the

• No tooling costs, but may require jigs • Low to high unit costs, depending on size and paint

• Aerospace • Automotive and transportation • Consumer electronics and appliances

• One-off to mass production

basecoat and topcoat. The role of the

automotive, consumer electronics and

base coat is to supply a monotone

appliance industries to justify robotic

backdrop for the high gloss topcoat. The

spraying systems.

Quality

Competing Processes

Speed

topcoat is clear and contains platelets

• Variable because it depends on the skill of the operator

• Hydro transfer printing • Powder coating • Vacuum metalizing

• Variable cycle time, depending on size and drying or curing time

the basecoat, the platelets or flakes are

or flakes of colour. As it is applied to

TYPICAL APPLICATIONS Spray painting is used in a vast range of applications including prototyping, repairs, low volume and mass production. It is used in the automotive industry for painting metalwork, and in the consumer electronics industry to colour plastic injection moldings.

COMPETING PROCESSES Powder coating is a dry coating

technique (page 356) with a finish similar to 2-pack thermosetting paints

Above

(see technical description, page 353). It

aluminium.The aluminium is locked

These swatches are a

produces a uniform and glossy coating.

onto the surface of the workpiece by a

range of Kandy colours

Some techniques are electrostatic and

basecoat and topcoat that are sprayed.

so attract the coating particles to the

It produces a highly reflective finish that

a new range of slightly

surface of the workpiece. Combined

can be tinted or coloured.

different colours.

Each basecoat produces

Colours can also be

with collection and recycling of the dry

matched to Pantone or

powder, up to 95% material utilization

QUALITY

can be achieved with powder coating.

The quality of surface finish in this process depends on the skill of the

Hydro transfer printing (page 408)

over different basecoats.

RAL reference charts.

The level of sheen on the coating is

can produce effects that were previously

operator. Spray coatings are built up

categorized as matt or egg shell, semigloss, satin or silk and gloss.

spray painted with airbrushes and

in thin layers, typically between 5 and

masking. It is a dipping process and

100 microns (0.0002-0.004 in.) thick,

reproduces patterns and print much

with the exception of high-build systems

more rapidly than spray painting.

such as combined filler-primer. It is

surface. Protective paints form a barrier

Vacuum metalizing (page 372) is essentially spray painting with pure

essential that the surface is prepared to

between the workpiece and atmosphere,

a high finish.

to prevent rusting,for example.

The surface finish may not be critical if the role of the coating is to protect the

TECHNICAL DESCRIPTION

Spray Coating Process

Spray guns are gravity fed, suction

Topcoat or lacquer

Spray mist

Paint supply

Spray gun Manually operated

as quick drying, antifouling, anti-mould or

illustrates a gravity-fed gun. They all

depends on the type and viscosity of paint.

are made up of 2 parts, the resin and the

antimicrobial properties.

catalyst or hardener. They are thermosetting and bond to the surface in a 1 -way reaction.

painting. The first is similar to the above,

controls the valve through which the

surface is prepared with filler and primer.

They are also hazardous to use because they

except that it is a mixture of paint with a high

pressurized air flows. The atomized

The primer may provide a surface onto

contain isocyanates.

level of lacquer, which produces a high gloss

paint is blown out of the nozzle and

which paint will adhere such as an acidic

makes a cone shape. Pressurized air

etch primer used to make a good bond with

pigment and a binder of acrylic emulsion,

glass, which is bonded onto the surface of

is blown out of the cap onto the cone,

metallic surfaces. Some topcoats require

vinyl emulsion or polyurethane, dissolved or

the workpiece at high temperatures (above

which forces it into an elliptical shape.

a basecoat to provide a coloured backdrop.

dispersed in water. They are applied to the

the melting point of the glass]. This limits

This gives the operator more control

Opaque topcoats can be applied directly onto

surface and dry as the water evaporates and

the finish to materials with a higher melting

because the shape can be adjusted to

the primer.

the binder adheres to the workpiece. They

point ceramics and metal, for instance.

Paints are made up of pigment, binder,

Water-borne paints are made up of

thinner and additives. The role of the binder

wood and other materials that are likely to

the surface in overlapping strokes.

is to bond the pigment to the surface being

expand and contract In their lifetime.

coated. It determines the durability, finish,

Solvent-borne paints (also known as

pot on the underneath instead of

speed of drying and resistance to abrasion.

alkyd and oil-basedl are made up of pigment

on top. The paint is drawn into the

These mixtures are dissolved or dispersed

and a binder of alkyd resin dissolved in

jet of air by suction. Pressure feed

in either water (water bornel or a solvent

thinners. Solvent-based paints are slow

systems are supplied by a paint pot

(solvent bornel. The ingredients of varnish, lacquer and

flexible pipe. The paint is pressurized

paint are essentially the same. Lacquers and

to force it into the spray gun.

varnishes can be pigmented, tinted or clear.

material.They can be replaced or

surface and so is prone to peeling and

enhanced by platelets of metallic,

to produce a cracked topcoat. Crackle

flaking.This is often the result of pinholes

pearlescent, dichroic, thermochromic or

varnish is painted over a colour. Onto this

or porosity in the coating, which allows

photoluminescent materials.

is applied a contrasting colour, typically

There is even a varnish employed

sprayed in booths that are modified

drying and off-gas polluting and harmful volatile organic compounds (VOCs).

All surface coatings are left for at least

catches the overspray and transfers it

paints and varnishes will dry in 2-4

to a central well where it settles and

COMPATIBLE MATERIALS

hours. Solvent borne products will take

separates ready for treatment.

roughly 4-6 hours.

g ol d on top of bl ack. Th e crackl e varn i sh

Almost all materials can be coated with

allows the topcoat to crack but not peel

paint, varnish and lacquer. Some surfaces

a seamless finish. Otherwise, masks and

as it dries and contracts.The effect is

have to be coated with an intermediate

because these tend to be manual

'pebbling', 'orange peeling',runs and

templates can be used to create different

similar to antique gold leaf.

layer, which is compatible with both the

processes, and the skill of the operator

sags. Pebbling is caused by a coating that

colours, patterns, logos and text. Masks

workpiece and topcoat.

will determine the quality of the finish.

is too dry; the thinner evaporates before

and templates can be made from tape,

DESIGN CONSIDERATIONS

it has had a chance to settle and smooth.

paper or cardboard for example.

The opportunities for paint effects and

only suitable for high-melting-point

ENVIRONMENTAL IMPACTS

quality are heavily dependent on the

materials such as ceramics and metal.

Solvent borne paints contain volatile

Water borne paints are prone to orange

There are many different techniques

peeling. As the name suggests, it is when

used to apply decorative effects. For

skill of the operator. With the correct

the surface resembles orange peel. It is

example, overlaying colours and tones

preparation and basecoat almost any

caused by the coating not flowing on the

using different spraying techniques

surface, or improper paint thinning. Runs

will produce graduation, shading and

and sags occur when there is too much

mottling. Marbling is achieved by

spraying applies coatings in line-of-sight,

wet coating material.

draping materials over a wet topcoat,

so deep undercuts and recesses are more

which drags and smears it over the

difficult to coat evenly. Electrostatic

DESIGN OPPORTUNITIES

basecoat. Covering it with a clear topcoat

There is an almost unlimited range of

seals in the pattern with dramatic effect

colours and finishes for paints. Standard

(see image, page 350).

colour ranges include RALand Pantone.

Colour is supplied by pigments, which are solid particles of coloured

A flock finish can be achieved by

Labour costs are typically high

Enamel paints that contain glass are

organic compounds (VOC). Since the

COSTS

ig8os automotive manufacturers have

combination of materials can be coated.

Tooling is not required. However,]igs or

been making the switch to water-based

An important consideration is that

framework may be necessary to support

paint systems to reduce their VOC

the workpiece during spraying.

emissions. It was not until the late 1990s

Cycle time is rapid but depends on the

that water-based systems were capable

size, complexity, number of coats and

of producing a finish that equalled the

techniques draw more spray to the

drying time. A small consumer electronic

previous solvent-based technologies.

surface, but there is always overspray.

product may be complete within 2 hours;

There is no size restriction. If the part

One system uses running water, which

12 hours to harden fully. Water borne

aircraft hangers.

including different materials, to produce

Some aesthetic problems include

finish. The second Is applying a coating of

are flexible and so are suitable for painting

thickness. The coating is applied onto

However, paint is not integral to the

underneath.

There are 2 different types of enamel

up of more than 1 layer. If necessary the

that is connected to the spray gun via a

Entire surfaces can be painted,

Painted surfaces are nearly always made

the paint into a fine mist. The trigger

Suction feed guns have the paint

the surface of the workpiece to corrode

Additives provide specific qualities such

emerged. They are so called because they

suit the application and required film

Rotating table or support jig

Another type of paint, 2-pack, has

approximately 3.45 bar (50 psi). This

use a jet of compressed air to atomize Workpiece

Conventional spray guns operate at

fed or pressure fed. The diagram

in contrast, a car may take several days.

Water-based paints are less toxic and easily cleaned with water.

will not fit in a spray booth or cannot be

Automated spraying techniques are

spraying adhesive followed by fibres of

moved then it can be sprayed on site.

very rapid. The parts are sprayed as the

booth or cabinet to allow the paints

cotton, paper, silk or similar material.

For example, very large aeroplanes are

productis assembled to avoidmasking.

to be recycled and disposed of safely.

Spraying is usually carried out in a -

Case Study

Spray painting a Pioneer 300 light aircraft Thfs is the Pioneer 300 (image i).The kit

In total 3 coats are applied and left to

is masked and the second topcoat colour

dry (image 5). The length of the drying tie

is applied (images 10 and 11).The finished

Aviation, Italy (image 2). The fuselage is

depends on the cure system. Once the primer

fuselage is assembled (image 12), ready for

assembled prior to spray painting. The joints

is sufficiently dry, the fuselage is rubbed

the wings.

between components are filled and rubbed

down with abrasive paper (image 7). Painting

down to make a smooth surface for the

several coats and then abrading the surface

primer. Masking is used to protect the glass

produces a much smoother finish. More coats

components are manufactured by Alpi

hood and areas of the bodywork (image 3). A 2-pack polyurethane paint is used to prime the surface. All paint sprayed in this way has to be filtered to make sure that there are no lumps, dust or other contamination

of primer are required if the finish is not good enough at this stage because the topcoat will show up every imperfection.

In preparation for the topcoat the top layer of masking tape is removed

that might block the spray nozzle (image 4).

(image 8). Underneath is a second layer

The first coat is sprayed on in overlapping

of masking,whichmarkswhere the

strokes (image 5). Each stroke is overlapped

topcoat will be sprayed up to. The edges

by about 50% to ensure a uniform coating.

are staggered in this way to avoid a build

The whole process is carried out in a

up of paint; otherwise the primer would

spray booth that cleans and circulates the air

produce a visible white line along the

continuously. It takes only a few minutes for

masked edge.

the giant fans to remove and replace all the air in the booth.

The topcoat is applied (image 9) to each component. The 'racing' stripe

Fluidized Bed Powder Coating Process

Electrostatic Spraying Process

Layer of powder builds up

Finishing Technology

Powder Coating

r

\

Electrically grounded metal workpiece

r

I'

This dry finishing process is used to coat a range of metalwork

Electrically grounded workpiece

Spray guns

by either spray or a fluidized bed. The powder adheres to the

Airflow through powder

Charged spray nozzle (-) Layer of powder builds up

Plume of electrostatically charged powder

workpiece electrostatically and is cured in an oven to produce a

Voltage I

glossy protective coating.

1 No tooling costs Low unit cost

Typical Applications

Suitability

a uniform finish.This is because the

• Automotive • Construction • White goods

• One-off to mass production

airborne orfluidizedpowderis drawn

TECHNICAL DESCRIPTIONS ELECTROSTATIC SPRAYING

FLUIDIZED BED POWDER COATING

to and adheres to the surface of the

Powder coating materials are made by

The fluidized bed technique is used

workpiece electrostatically.There is

blending together the ingredients; resin,

to apply plastic coatings to parts

greater electrical potential difference

pigment, filler and binder. The mixture

both with and without the addition of

where the coating is thinnest, which

is then ground into a fine powder so that

electrostatic energy.

encourages the powder to build up in a

each particle contains the necessary

uniform manner.

ingredients for application.

Quality

Related Processes

Speed

• High quality, gloss and uniform

• Dip molding (as a coating) • Galvanizing • Spray painting

• Rapid application depending on size of part and level of automation • Curing takes 30 minutes or more

Thermoset coatings are the most

INTRODUCTION

The most common method of

RELATED PROCESSES

commonly used and have similar

Powder coating is primarily used to

application is electrostatic spraying

Powder coating is often used in

characteristics to 2-part epoxy, or

protect metalwork from corrosion and damage: the polymer forms a durable skin on the surface of the metal.

because it is more versatile. Fluidized

bed is limited by the size of the tank and colour batches, and is therefore

conjunction with other finishing processes for particularly demanding or outdoor applications. For example,

polyester paints.The baking process forms cross-links in the polymerthat increase hardness and resistance to acids

The most common powder coating

The fluidized powder is made up of the same ingredients as those used in

electrostatic spraying. In fluidized bed

technique is electrostatic spraying. In

coating, the powder is contained in a

this process the powder is suction fed

tank. Air is pumped through it to create

or pressure fed to the spray gun. Air

a powder-air mixture that is dynamic,

pressure forces it through the spray

similar to a liquid. The part is dipped into

nozzle, which applies a high-voltage

the fluidized powder, which adheres to its

negative charge to each particle. This

surface. For thermosets, the powder has

negative charge creates electrical

to be cured after dipping in the same way

potential difference between the particle

as electrostatic spraying.

Because it is a polymer there are many

most suitable for mass production

steelwork must be galvanized (page 368)

and chemicals. In contrast, thermoplastic

associated benefits such as a range of

applications such as wire rack shelves

prior to powder coating for a durable and

coatings do not cross-link when heated.

vivid colours and protective qualities that

in fridges and automotive parts. It is

long-term finish. Without galvanizing,

Instead, the dry powder coating melts

and electrically grounded workpiece. The

are engineered to suit the application.

more commonly used for thermoplastic

the steel would rust beneath the powder

and flows over the surface as it warms

electrostatic force draws the plume of

thermoplastic coatings. The workpiece

Furthermore, it is a dry process that has

powder coatings.

coating, causing it to blister and flake.

up. Cooling re-solidifies the polymer to

powder towards the workpiece, causing

is pre-heated to just above the melting

produce a smooth and even coating.

it to wrap around and lightly coat the

temperature of the thermoplastic and

reverse side. The negatively charged

dipped into the fluidized powder, which

DESIGN OPPORTUNITIES

polymer powder adheres to the workpiece

adheres to the surface of the workpiece

These processes are used to provide

with static energy. All parts of the

on contact. In this way, thick coatings can

alayer of protection, often with the

workpiece must be exposed to the stream

be applied in a single dip or with multiple

addition of col our. There are many

of powder to ensure a uniform coating.

dips. Thicker coatings provide a greater

low environmental impacts.

Alternatives to powder coating

TYPICAL APPLICATIONS

include wet spray painting methods

the 1960s for in-line coating aluminium

Powder coating is suitable for both

extrusions (page 360) such as window

functional and decorative applications.

(page 350), especially 2-part thermosetting paints which are

frames. Architects and designers enjoyed

Functional applications include

extremely durable.These techniques are

Powder coating was developed in

the possibilities of powder coating and so

products for abrasive, outdoor and

m ore suitabl e if a vari ety of m ateri al s are

demand increased for powder coating on

high-temperature environments

being coated, or if the materials cannot

other metal s, in cludin g steel. Currently, aluminium and steel are the most widely

such as automotive, construction and agricultural parts. Powder coating is also

withstand the high temperatures in the powder coating baking process.

associated benefits, especially for application in children's play areas or publ i c furn iture, for exam ple.Therange

powder coated materials, but many other

used in white goods that demand good

materials are being explored that could

temperature and chemical resistance.

QUALITY

speckled, textured and wood grain

benefit from a powder coated finish,

Other than that, it is used a great deal for

The polymer coating is baked onto the

finishes are possible.

including plastics and wood composites.

parts of indoor and outdoor furniture,

workpiece in an oven, which produces

The powder can be applied as an electrostatic spray or in a fluidized bed.

domestic and office products.

of colours is unlimited and even metallic,

As well as pigments, many other

a glossy, durable and tough finish. By its

additives can be mixed into the powder.

very nature, powder coating produces

Additives are used to improve the

The whole process takes place in a

spray booth. The parts are generally fed into and out of the booth on a conveyor

It is frequently used to apply

level of protection as well as smoothing over rough surfaces and joints.

This technique, without the addition of

belt, which provides the electrical

electrostatic energy, improves the coating

grounding. After spraying, the workpiece

of wire racks and other parts that cause

is baked in an oven at approximately

problems during electrostatic spraying

200°C (392°F) for 30 minutes or so.

due to the 'Faraday cage' effect.

Case Study

Electrostatic spraying a gate In this case study, Medway Galvanising are

the factory. The operator is protected as he

powder coating some previously galvanized

sprays a plume of electrostatically charged

steelwork. Preparation is key to the success

powder over the metalwork (image 4).

of the finish. First of all, the parts have been

The powder coated finish is very

galvanized (page 368) to protect the base

delicate at this point, so handling is kept

metal, which is then sanded to produce an

to a minimum. The part is loaded onto a

even higher quality finish (image 1).

conveyor that takes it through a camelback

The cleaning process consists of a series of 10 baths that progressively clean,

oven (image 5), The temperature inside the oven is 2000C (392°F).The part is heated

degrease and prepare the surface for

as it is conveyed up and over the heating

powder coating. A bath of zinc phosphate

compartment, hence the name. At this

(image 2) provides an intermediate binding

temperature the thermosetting polymer

layer between the clean galvanized surface

chemically reacts, forming cross-links

and the thermosetting powder.

between the molecular strands to produce

The metalwork, in this case part of a

a very durable and tough coating. It is a

steel gate, is loaded onto an electrically

gradual process and lasts 30 minutes or so.

grounded conveyor belt that delivers it

The cured part has a rich-looking red

into the powder-coating booth (image 3).

plastic coating (image 6). It is still very warm

This process is manually operated, due to

and is left to air dry for a short period while

the level of versatility that is required in

the thermosetting plastic fully hardens.

coating's UV stability, chemical

time consuming and less practical.Thin

not prepared effectively. Preparation

hardness and durability. Certain grades

resistance, temperature resistance and

films can be very difficult to achieve, especially with electrostatic methods

consists of anumber of cleaning and

offer added protection against UV.

durability, for example. Antimicrobial additives can also be incorporated, which

The choice of thermoplastic and

Thermoplastic powders include

and thermosetting powders.

for powder coating.These stages are essential to produce a sufficient bond

polyethylene (PE), polypropylene (PP), polyamide (PA), polyvinyl chloride (PVC),

DESIGN CONSIDERATIONS

between workpiece and coating to

fluoropolymers and many more. These

Part design will affect the choice

ensure its longevity.

coatings make up a small percentage

inhibit the growth of mould, mildew and bacteria on the surface of the coating.

etching baths, which ready the surface

thermosetting powders provides

of technique. Each technique is

designers and manufactures with a large

generally suited to different materials:

of the powder coating market. They

COMPATIBLE MATERIALS

scope of opportunity.The coating can be

thermoplastic powders are coated

Many metals can be coated in this

can be built up in thick layers using the fluldlzed bed method to provide superior

engineered with additives, binders and

using the fluldlzed bed technique and

way. However, the majority of powder

performance characteristics.

pigments to suit a specific application if

thermosets are electrostatically sprayed.

coating is used to protect and colour

the volumes justify It. Otherwise, there

But this is not always the case.

aluminium and steelwork,Technologies

COSTS

higher with powder coating than wet

are emerging that make it possible

There are no tooling costs, although

that can be utilized in standard powder-

and widely used process. Most parts

to powder coat certain plastics and

equipment costs are relatively high.

coated finishes.

can be coated in this way. Fluldlzed

composite wood panels, although they

bed coating offers improved coverage

Is a vast range of polymer characteristics

There is very little risk of powder

Electrostatic spraying is a versatile

coatings running into sags In either

on complex and intricate geometries,

technique, even when a heavy build up

especially if they will cause the 'Faraday

is required.The thickest coatings can be

cage' effect in electrostatic spraying.

achieved with fluldlzed bed techniques,

Surface finish is determined by the

ENVIRONMENTAL IMPACTS Material utilization tends to be much

spray painting methods. This 1s partly due to electrostatically charging the particles, but also because It Is possible

One coat is usually sufficient, so cycle

to collect and filter powder overspray.

are new and relatively specialist. It is

time is very rapid. The baking process to

Production lines powder coating with

also possible to powder coat glass by the fluldlzed bed method.

cure the resin adds approximately half

continuous colour can achieve over 95%

an hour to the cycle.

powder utilization.

The coating materials include

This is a simple process: powder is

Everything requiredforthe coating

th erm opl asti cs an d th erm osets. Typi cal

easy to spray and the potential electrical

is contained in each particle: resin,

which can be built up by dipping a hot

quality of the finish prior to coating,

thermosets Include epoxy, polyester,

difference actively encourages a uniform

pigment, filler and binder. Therefore It is

workpiece several times In thermoplastic

unless a very heavy coating is produced

acrylic and hybrids of these polymers.

coating to develop.Therefore, labour

not necessary to suspend the powder in a

powder. Electrostatic spraying can also

in a fluldlzed bed. Castings, for example,

They are characterized by good resistance

costs can be quite low.

solvent or water, which can be harmful to

produce thick coatings, but it Is more

will produce a textured finish if they are

to chemicals and abrasion, andtheir

Featured Manufacturer Medway Galvanising Company www.medgalv.co.uk

the operator and environment.

Anodizing Process

s

'{r

£ Cathode (-) Workpiece: anode

TECHNICAL DESCRIPTION

The surface of aluminium, magnesium and titanium can be

Anodizing has 3 main stages: cleaning

anodized to form a protective oxide layer. It is naturally light

Dilute sulphuric acid electrolyte

U

OOC COC

y

and etching, anodizing and sealing.

In stage 1, the cleaning and etching

grey, but can be electrolytically coloured, or dyed, with a range of

baths prepare the workpiece for anodizing. The surface is either etched

vivid colours including red, green, blue, gold, bronze and black.

Stage 1; Cleaning and etching

Stage 2: Anodizing

Stage 3: Sealing

or brightened in chemical baths. Etching produces a matt or dull finish and minimizes preparatory operations. Costs

Typical Applications

Suitability

Brightening (chemical polishingl

15 minutes to produce 5 microns

colour is produced by light interference.

• Tooling is not usually necessary • Low unit costs, but increasing with film thickness

• Architectural • Automotive • Consumer electronics

• One-off to high volumes

produces a very high gloss surface

(0.00019 in.) of anodic film.

An alternative technique uses tin instead

suitable for decorative applications. Alkali

Quality

Related Processes

Speed

• High quality, lightweight and very hard

• Powder coating • Spray painting

• Moderate cycle time (approximately 6 hours)

Hard anodizing produces films up to

of cobalt. This is popular, but the colour is

surface of the metal. In doing so, a small

less resistant to UV light than the Anolok™

neutralize each other.

amount of base material Is consumed

system. The third technique is known as

In stage 2, the anodizing takes place In

INTRODUCTION

Anodizing adds an anodic film to the

and acid baths are used in succession to

(roughly half the thickness of the anodic

'dip and dye'. In this, the colour is created by

an electrolytic solution, which is generally

film). This will affect the roughness of the

simply dying the anodic film prior to sealing.

dilute sulphuric acid. A current Is passed

surface. Only thin coatings will retain a high

This process can produce the widest range

between the workpiece (anode) and

gloss finish and these are therefore not

of colours, but it Is the least UV stable and

of these processes include building up

electrode (cathode). This causes oxygen

suitable for high-wear applications.

Colour is applied In 3 main ways. The

consistent, so is generally only used for

Anodizing refers to a group of processes

50 microns (0.0020 in.) thick. It is used for

thick layers, a wide colour range and how

to gather on the surface of the part, which

that are used to treat the surface of

more demanding applications because

easily they can be repaired.

reacts with the base metal to form a porous

Anolok™ system, recommended for outdoor

metals. The workpiece is made the

the thicker film Improves wear and

oxide layer (aluminium produces aluminium

applications, is an electrolytic colouring

Is sealed in a hot water bath. Sealing the film

oxide). The length of time in the bath, the

process. A range of colours are created by

produces the hardwearing and weather-

anode and submerged in an electrolytic

temperature resistance.

temperature and the current determine the

depositing cobalt metal salts in the porous

resistant characteristics that are associated

rate of film growth. It takes approximately

anodized surface prior to sealing. The

with anodizing.

are relatively expensive metals and are selected for their superior strength

solution.The process builds up the naturally occurring oxide layer on the

Aluminium, magnesium and titanium

TYPICAL APPLICATIONS

to weight ratio. Anodizing improves

surface of the metal.The film is hard,

Anodizing Is used to protect and enhance

the material's natural resistance to

protective and self-healing; aluminium

metal for both Indoor and outdoor use.

weathering without significantly

oxide is inert and among the hardest

Indeed, most aluminium in the

increasing weight, and is therefore the

certain colour systems are guaranteed

automotive, construction,leisure and

most popular surface technology.

for up to 30 years.

strength, so electrical components can be

The appearance of the finished piece is determined by the quality of the mill finish prior to anodizing. It is Important that the material is from the same batch

mounted onto them.

materials known to man. There are 3 main methods, which are natural anodizing, hard anodizing and chromic acid anodizing. Most

consumer electronics industries is treated this way.

Well known examples include the

Chemically colouring stainless steel Is a similar process: the naturally occurring passive film on the surface of themetal is enhanced.

decorative and indoor applications. In stage 3, the surface of the porous film

Anodic films have very high dielectric

Anodizing can be applied to all types of finishes and textures, Including satin,

architectural, automotive and general

Maglite, Apple IPod and G5 Powermac.

anodizing is carried out in sulphuric

Other products Include karabiners and

acid using the natural or hard anodizing

general climbing equipment,televisions,

methods. Chromic acid anodizing is a

telephones, appliances, control panels,

Anodizing is unmatched for surface

It is not possible to colour match to

removed by laser engraving (page 248) orphoto etching (page 292).This is

more specialized process.

picture frames, cosmetic packaging, shop

treating aluminium,magnesium and

specific swatches such as Pantone.

used to create patterns, text or logos by

fronts and structural products.

titanium. It Is light, very hard, self-healing

contrasting the colour of the anodized

BeoLab 4000 speakers

and resistant to weathering.The anodic

DESIGN OPPORTUNITIES

surface with that of the base metal.

are produced by

film is Integral to the underlying metal and so will not flake or peel like some

Anodizing has many benefits Including hardness, ease of maintenance, colour

DESIGN CONSIDERATIONS

coating processes. It has the same

stability, durability,heat resistance and

Anodizing adds a film thickness to the

melting point as the base metal and

corrosion resistance, and it is non-toxic.

dimensions of the product, but the

Natural anodizing produces finishes 5-35 microns (o.oooig- 0.0014 in.) thick and grey in colour.The finish can be

RELATED PROCESSES

coloured to range of vivid shades, such as the Bang & Olufsen BeoLab 4000

Painting (page 350) and powder coating (page 356) addalayer of material to the

speakers (see image,opposite).

surface of the metal.The advantages

if it Is used together because different

QUALITY

batches will have varying colour effects.

brushed, embossed and mirror polished.

The anodic film can be selectively Above

The vivid colours of these Bang & Olufsen

anodizing aluminium.

Case Study

> Anodizing automotive trims Heywood Metal Finishers use the Anolok™

hardwearing. After this, they are sealed in

colouring system. This technique is used to

hot water with additives at a temperature

anodlze parts for exterior and demanding

of 980C (208.4°F).

applications such as in the construction and

The anodic film is non-toxic and can

automotive industries. It is distinguished

be handled immediately after sealing.

from other processes by the colouring phase:

The parts are removed from the jig and

cobalt metal salts are deposited 1n the porous

packed (image 7).

film during colouring.The colours (grey, bronze, gold and black) are produced by light interference and so are more durable and less

prone to fading than other methods. In this case, aluminium extrusions are being anodized for automotive

application (image i).The lengths are loaded onto an adjustable jig, which is set up to accommodate different lengths of metal (image 2). The parts are mounted at a slight incline to allow the chemicals to drain off during dipping (image 3). There are 10 baths in the anodizing cycle and the whole process can take up to 6 hours

(images 4 and 5). At the other end of the plant some aluminium parts are being anodized.

They are dipped into the sulphuric acid electrolyte for between 15 and 5o minutes (image 6). Longer dip times produce thicker films, which are generally more

etching and cleaning process usually

Variation in the chemical composition

ENVIRONMENTAL IMPACTS

compensates forthis as it removes about

of the metal affects the colour. This is

Waste from anodizing production

the same amount of material. However,

a concern both for welded joints and

is non-hazardous. Companies are

this will depend on the anodizing

for fabrications containing metal from

monitored closely to ensure they do not

system and hardness of the material

different batches.

because softer material will etch more

allow contamination into wastewater

This is a dipping process and so liquids

or landfill. Although acidic chemicals are

rapidly.Therefore, it is essential that the

have to be able to drain from the parts.

used in the anodizing process there are

anodizing company is consulted for parts

The maximum size of part that can be

n o h azardous by-products.

that have critical dimensions.

anodized is limited by the capacity of

The colouring process will determine

the UV stability of the part.The AnoM™

The baths are continuously filtered

the baths, and fabrications can be up to

COSTS

and recycled. Dissolved aluminium

7 x 2 x 0.5 m (23 x 6.6 x 1.6 ft).

There are no tooling costs.but jigs may

is filtered from the rinse tanks as

colouring system, which applies cobalt

have to be made up to accommodate the

aluminium hydroxide, which can be

metal salts electrolytically,1s guaranteed

COMPATIBLE MATERIALS

parts in the anodizing baths. Cycle time is

safely recycled or disposed of.

for up to 30 years in architectural

Aluminium, magnesium and titanium

approximately 6 hours.

applications, but the colour range is

can be anodized.

limited to grey, bronze, gold and black.

This process is generally automated, so labour costs are minimal.

Anodized surfaces are non-toxic.

Electroplating Process

Connected to power source (-) Connected to power source (+)

Finishing Technology

Wire jig

Electroplating

Electrically charged workpiece

QUALITY

This is an electrolytic process used to apply a thin film of metal

Electroplated films are made up of

to another metal surface. A strong metallurgical bond is formed

Electroplated metal coating

pure metal or alloys. An integral layer

between the base material and coating. Electroplating produces

is formed between the workpiece and

a functional and durable finish.

forms a strong metallurgical bond with

metal coating because each metal ion

its neighbour.

Metals that will not plate to each Costs

Typical AppUcations

Suitability

other can be joined with intermediate

• No tooling costs, although jigs may be required to support parts • High unit costs, determined by materials

• Consumer electronics • Furniture and automotive • Jewelry and silversmithing

• One-off to high volume production

layers that are compatible with both the coating and base material. For

Quality

Related Processes

Speed

• Coating material is chosen for specific qualities such as brightness or resistance to corrosion

• Galvanizing • Spray painting • Vacuum metalizing

• Moderate cycle time, depending on type of material and thickness of coating

\

and corrosion resistance of a gold

TYPICAL APPLICATIONS

is used in critical applications to improve

Electroplating is used to produce

This process is used a great deal by

conductivity and ensure a tarnish free

jewellers and silversmiths, who can form

surface finish.

replenished by dissolution of the metal anodes. The anodes are suspended in the

The thickness of electroplating

degreaslng In a hot caustic solution. Then parts are Immersed in a dilute cyanide

depends on the application of the product

solution, to remove surface oxidization,

and material. For example, nickel

the workpiece prior to electroplating.

which is neutralized in sulphuric acid.

used as an intermediate levelling layer

up to 25 microns (0.0098 in) thick,

then coat them with silver or gold to give

Electroplating is the most reliable,

are deposited on the surface of the

a bright, inert and tarnish-free surface

repeatable and controllable method

DESIGN OPPORTUNITIES

workpiece in an electrochemical process.

finish. Examples include rings, watches

of metal plating.

The main benefit of this process is

beakers, goblets, plates and trays.

electrolyte In a perforated container.

The quality of surface finish is largely dependent on the surface finish of

have suitable mechanical properties,

a combination of the properties of the

The cleaning stage consists of

and protection to the brass.

The metal coating is too thin to cover

There are many other techniques

builds up on the surface of the workpiece the Ionic content of the electrolyte Is

onto a jig to support them through the

less than i micron (0.000039 in.)

and bracelets.Tableware includes

stages, which are cleaning, electroplating and polishing. The parts are mounted

electroplating process.

parts in less expensive materials that

Electroplated metals benefit from

As the thickness of electroplating

intermediate layer is used as a barrier

on metals.Thin layers of metal,from

RELATED PROCESSES

Electroplating is made up of 3 main

electroplating. Thereto re, a nickel and provides a strong inter metallic bond

INTRODUCTION functional and decorative finishes

example, brass will affect the strength

TECHNICAL DESCRIPTION

scratches and other imperfections.

tha,t it can produce the look, feel and

used to coat materials with metal,

benefits of 1 metal on the surface of another, allowing parts to be formed in materials that are less expensive or have

Electroplating occurs in an electrolytic solution of the plating metal held in

may be up 10 microns (0.00039 in.), while electroplated gold needs to be

suspension in Ionic form. When the

only 1 micron (0.000039 In.) thick for

workpiece is submerged and connected to

decorative applications.

a DC current, a thin film of electroplating

After electroplating the parts are

forms on its surface. The rate of

finely polished (buffed) In a process

deposition depends on the temperature

known as 'colouring over'.

and chemical content of the electrolyte.

brass combines the strength and reduced

pieces that will not come into prolonged

including spray painting (page 350) with conductive paints, galvanizing (page

cost of brass with the long lasting lustre

human contact can be plated with

368) and vacuum metalizing (page

suitable properties for the application.

of silver.

rhodium or nickel for an even longer

372). Spray painting technology has been

Electroplating then provides them with a metal skin that possesses all the

is hard, highly reflective and resistant to

18 ct is 75% gold by weight; 14 ct is 58.3%

most chemicals and acids. It is used for

gold; 10 ct is 41.1% gold and 9 ct is 37.5%

improving steadily.There are now paints

desirable aesthetic qualities.

decorative applications that demand

gold. Many national standards, including

superior surface finish such as medals

the US standard, allow 0.3% negative

and trophies.

tolerance: the British standard does not.

2 materials. For example, silver-plated

It is possible to plate certain plastics in an electrochemical process. However, this

Trophies, medals, awards and other

lasting and brighter finish. Examples of electroplated plastic

The most common electroplating

is not strictly electroplating. It is a slightly

include automotive parts (gear sticks,

with high metallic content. Finishes can

different process because the finish can

door furniture and buttons), bathroom

be polished and buffed like solid metal.

only be achieved by coating the plastic

fittings, cosmetic packaging and trims on

These processes rely on the polymer

nickel, silver, gold and rhodium. Each of

mobile phones, cameras and MP3 players.

carrier within which the metal platelets

these materials has their own particular

Electroplating has many important

are suspended. Like vacuum metalizing,

properties and benefits.

with an electroless intermediate layer. This provides a stronger base for the desired material to be plated onto, but it

functional roles, such as improved levels

these surface coatings do not form a

is difficult to produce a long lasting finish

ofhygiene, ease of joining (such as silver and gold soldering) and improved

metallurgical bond with the workpiece.

because there is no metallurgical bond between the coating and substrate.

thermal and electrical conductivity. Gold

materials include tin, chrome, copper,

Gold is a unique precious metal

Silver is less expensive than the

with a vibrant yellow glow that will not

previous metals. It is bright and highly

oxidize and tarnish.The alloy content of

reflective, but the surface will oxidize

Rhodium is a member of the platinum

the electrolyte bath will affect whether

more readily and so has to be frequently

family and is very expensive. It has a long-

it has a rose or green tint. The purity of

polished or'coloured over'to maintain its

lasting lustre that will not tarnish easily

gold is measured in carat (ct), or karat

brightness. Silver's tendency to oxidize is

in normal atmospheric conditions, and

(kt) in North America: 24 ct is pure gold;

used to emphasize details by'blackening'

it in a chemical solution and then

Case Study

polishing raised details back to bright silver. This technique is often used in

-> Silver electroplating nickel-silver cutlery

jewelry to emphasize relief patterns. Nickel and copper are often used as

The quality of the finish is largely dependent

To prepare the metal for electroplating it

The electroplated parts are cleaned and

intermediate layers.They help to produce

on the smoothness of the finish prior to

is immersed in a series of cleaning solutions,

dried (image 6). At this point the finish is

a very bright finish because they provide

electroplating.These nickel-silver spoons are

including a dilute cyanide solution, in which

not a high gloss. A brightening agent is

polished to a high gloss In preparation for

the surfaces of the spoons can be seen fizzing

sometimes added to the electroplating

silver electroplating (images i and 2).

(image 4). All traces of contamination, such as

bath to produce a more reflective finish. The

polishing compound and grease, are removed.

surface is improved and finished with a very

a certain amount of levelling. If they are

built up in sufficient quantities they will

They are being coated entirely with a

cover small imperfections and produce

In this case 25 microns (0.00098 in.) of

fine iron powder polishing compound, known

a smooth layer to electroplate onto.

thin layer of silver and so they are connected

As intermediate layers they provide a

to the DC current with a loose fitting wire

silver is being electroplated onto the surface

as 'rouge'. This is applied in a buffing process

(image 3). The parts are agitated in the

(image 5). This takes approximately an hour

known as 'colouring over'to produce the

electroplating bath so they receive an even

in the electroplating bath.The whole process

highly reflective finish (image 7).

coating. If they were jigged on aframe there

is computer-controlled to ensure maximum

would be a small area left unplated.

precision and quality of surface finish.

barrier between the electroplated metal and workpiece. This Is especially useful for metals that either contaminate each other, or are not compatible. Copper is an inexpensive material for

electroplating, but tarnishes very quickly and so Is rarely used as a topcoat.

33 -a

o

DESIGN CONSIDERATIONS Parts have to be connected with a DC

¦ current to be electroplated. This can be

wired' mounted a rigid 'loose jig. Loose I done in 2 or ways: they onto are either wiring is an effective way to hold parts forlowvolume electroplating. Jigs have

a fixed point of contact, which Is visible after electroplating.This Is minimized by contacting the workpiece between 2

The plastic that is most commonly electroplated is acrylonitrlle butadiene styrene (ABS). It is able to withstand the 6o0C (i4o0F) processing temperature,

small points, or on an inconspicuous part

and it is possible to etch into the surface

of the product.

to form a relatively strong bond between

It Is possible to mask areas with

it and the electroless plated metal.

special waxes or paint so they are not electroplated.This will increase unit cost. Chrome plating was used extensively in the automotive and furniture industries. It is still used a great deal but

4

COSTS There are no tooling costs, but jigs may

ENVIRONMENTAL IMPACTS

be required to hold the parts In the tank.

Many hazardous chemicals are used in

Cycle time depends on the rate

all of the electroplating processes.These

Is steadily being replaced, due to the

of deposition, temperature and

are carefully controlled with extraction

heavy metal content of the process. At

electroplated metal. It Is approximately

and filtration to ensure minimal

present there is nothing to compete with the brightness and durability of chrome

25 microns (0.00098 in.) perhourfor

environmental impact.

silver and up to 250 microns (0.0098 in.)

electroplate onto a nickel basecoat.

per hour for nickel.The rate of

microns, and these processes apply only

Similar levels of reflectivity can be

deposition will affect the quality of the

the necessary amount of material.

achieved with other metal combinations,

electroplating: slower processes tend to

but they may not be as durable.

produce more precise coating thickness. Labour costs are moderate to high

Coating thickness is measured in

Gold and silver are inert and suitable

for all types of products including medical implants, beakers,bowls and

COMPATIBLE MATERIALS

depending on the application. For

jewelry. Nickel should not be used in

Most metals can be electroplated.

example, silverware and jewelry has to

contact with the skin because it is

However, metals combine with different

be finished to a very high level because

irritating and can be poisonous.

levels of purity and efficiency.

appearance and durability are critical.

Featured Manufacturer

BJS Company www.bjsco.com

7

\

TECHNICAL DESCRIPTION

Hot Dip Galvanizing Process

There are typically 6 baths in the hot dip galvanizing process. The first U are in the cleaning and degreasing stage

Finishing Technology

of the process. The parts are dipped in

Galvanizing

hot caustic acid for degreasing. Next,

the parts are dipped in 2 progressive hydrochloric acid pickling baths to remove all mill scale and rust. Lastly,

In this process steel and iron are hot dipped In molten zinc that

they are washed at 80°C (176°Fj in

alloys to its surface metallurglcally and provides electrochemical

preparation for the zinc flux.

protection against the elements. It produces a bright, distinctive

dipped in a flux of hot zinc ammonium

During stage 2 the metalwork is chloride to condition the clean surface

pattern on the surface, which over time becomes dull and grey.

for galvanizing and ensure a good flow of zinc over the internal and external surfaces of the metalwork.

Costs

Typical Applications Architectural and bridges Automotive Furniture

Quality • Excellent protection • Appearance affected by quality of steel

Finally, the metal work is immersed

Suitability

The zinc will react with atmospheric

explosive design elements that include

in a bath of molten zinc, which is

elements more readily than iron and

sealed tubes and blind corners. All

maintained at 450oC |8/iO°F). The zinc

forms a deposit over the exposed area

weldingslag,grease an dp ainthaveto

bonds with the iron metallurgically to

be removed pre-treatment.

create a zinc-iron alloy that is inherent

One-off to mass production

that protects the base material from

Competing Processes

to the surface of the metalwork. Strata

further corrosion. Electroplating Spray painting Vacuum metalizing

INTRODUCTION Zinc and iron combine to produce a vety

effective alloy that increases the life of steelwork and ironwork substantially. Unprotected metalwork continuously corrodes and its structure is undermined, whereas galvanized metalwork is protected from the elements and so

• Rapid cycle time (typically complete within 10 minutes)

removes excess zinc and produces a more uniform, even coating.This is particularly useful for threaded fasteners and other small parts that require accurate coating. Galvanizing is resilient to aggressive handling and over the last 150 years has proven to provide a long-lasting, tough and low-maintenance coating.

The look of the zinc coating is also

QUALITY

affected by the quality of the steel.The final effect can appear bright and shiny

metallurgical bond, only steel and iron

to dull and grey; the latter is caused by

can be coated in this way.

The costs of this process are low,

clean finish. Over time and with exposure

This is a versatile process that can be

especially in the long term. No specific

to atmospheric conditions this becomes

used to protect small items such as nuts

tooling is required. Cycle time is rapid.

dull and grey. It is tough and protects the

and bolts as small as 8mm (0.315 in.)

of finish is affected by the skill of the operators, amongst other factors.

oxygen, water and carbon dioxide. Levels

to 12 m x 3 m (40 x 10 ft). Structures larger than this can be fabricated post-

Victorian steel roofre-galvanizedforthe

(0.0000039 in.) per year for indoor uses

galvanizing. Complex and intricate

ENVIRONMENTAL IMPACTS

first time (see image, opposite).

to 4-8 microns (0.00015- 0.00031 in.) per

shapes can be galvanized in a single

This process can increase the life of

year for outdoor applications near the

operation, including hollow and open-

steelwork to between 40 and 100 years.

coast. A typical coating is between 50 and

sided vessels.

Station, for example, has recently had its

During galvanizing, zinc bonds with

iron metallurgically to produce a layer of zinc-iron alloy coated by a layer of pure zinc. The coating is therefore integral to

Galvanized steel can be recycled and so has an almost indefinite lifespan.

TYPICAL APPLICATIONS Typical applications include architectural steelwork such as stairwells, walls, floors and bridges; agricultural hardware, automotive chassis and furniture.

the base material; the intermediate alloy layer is very hard and can sometimes exceed the strength of the base material. Galvanizing is carried out in 2 ways:

hot dip or centrifugal galvanizing.They are essentially the same, except that

in centrifugal galvanizing the parts are dipped in baskets and then spun after submerging in molten zinc. This

COMPETING PROCESSES Other techniques used to coat materials

with metal include electroplating (page 364), vacuum metalizing (page 372) and spray painting (page 350) with conductive paints. Unlike these processes, galvanizing is limited to coating steel andiron with zinc.

150 microns (0.0020- 0.0059 in.) thick

depending on the application technique. The thickness of the coating is normally determined by the thickness of the base metal.The exceptions are centrifugal galvanized coatings, which produce a

slightly thinner coating, or thicker coatings produced by roughening the surface of the part or adding silicon to the steel during production. By its very nature the zinc coating protects the steel, even if it is penetrated.

pure zinc. The dipping process can last up to 10 minutes, depending on

the depth of zinc coating required. The parts are gradually withdrawn from the zinc bath to allow excess zinc to drain off.

Labour costs are moderate; the quality

diameter, to very large structures up

of corrosion can vary from o.i microns

retains its structural integrity. Waterloo

process, and the outer layer is typically

COSTS DESIGN OPPORTUNITIES

base material against corrosion from

concentration are built up during the

Because galvanizing relies on a

steel with high silicon content.

When the steelwork is removed from the

galvanizing bath the zinc has a bright,

of zinc-iron alloy layers of varying

COMPATIBLE MATERIALS

It is widely accepted that half of all new steel produced is used to replace

DESIGN CONSIDERATIONS

corroded steel. In some countries this

Galvanizing coats the entire surface of a

costs up to 4% of GDP. Galvanizing

part with zinc. High temperature tape,

dramatically increases the longevity

grease or paint can be used to mask

of steel fabrications, reducing their

Above

environmental impact.

The roof ofWaterloo

areas. Certain hollow geometries can be

galvanized only on the outside, but this requires special coating techniques.

The galvanizing bath is maintained at

The process uses zinc efficiently to protect the surface of steelwork. After each dip the unused zinc drains back into

4500C (84O0F), so all parts must be able

the galvanizing bath for reuse. Zinc can

to withstand that temperature. Another

be recycled indefinitely without loss of

important consideration is potentially

any physical or chemical properties.

Station in London was galvanized nearly 100 years ago. It has not needed re-galvanizing

until recently and will probably last another century before any further treatment.

Case Study

Hot dip galvanizing steelwork First of all the parts are cleaned and checked

its temperature has by now been raised to

for any air or solution traps that may cause

8o0C (1760F). The parts are then dipped into a bath of

problems during the galvanizing process. The metalwork is then rigged onto beams at

molten zinc at 4500C (84O0F) (image 6).The

a 30° angle to facilitate draining {images i

zinc spits as it comes into contact with the

and 2). Drainage holes may have to be

cooler metal. During galvanizing the surface

designed into the product to ensure that

of the molten zinc is continuously skimmed

solution can drain off during the process.

to remove any contamination and flakes of

The metalwork is moved through to the galvanizing plant where it is dipped

metal that might affect the quality of the galvanized finish (image 7).

in progressive cleaning and pickling baths (image 3).The preparation, cleaning

The parts are removed from the molten zinc slowly to allow excess zinc to drain back

and base material content determines

into the bath (image 8). The use of zinc is

the quality of the galvanized part, so

very efficient; a ratio of roughly 1:15 of zinc to

this stage of the process is essential to

metalwork is usual. The parts are removed

ensure consistent levels of quality. The

from the bath and air dried or quenched,

penultimate bath (image 4) contains a flux

according to the customer requirements

that conditions the surface in preparation

(image 9) and they are loaded for delivery

for the hot dip galvanizing. The metalwork

(image 10).

is removed from the flux steaming in preparation for galvanizing (image 5);

3

4

Vacuum Metalizing Process

Vacuum pulled lO"'' millibars

Finishing Technology

Vacuum Metalizing Also known as physical vapour deposition (PVD) and sputtering, the vacuum metalizing process is used to coat a wide range of materials in metal to create the look and feel of anodized

INTRODUCTION

models in suitable materials can be

This process combines very high vacuum

coated to give the look and feel of a metal

and an electrical discharge that vaporizes

part. In contrast, mass produced metal

almost pure metal (most commonly

parts can be coated for added value.

aluminium) in a vacuum deposition

aluminium, chrome, gold, silver and other metals.

No tooling costs, but jigs are required Moderate unit costs

Typical Applications

Suitability

• Consumer products • Reflective coatings • RF. EMI and heat shielding

• One-off to mass production

application. Cosmetic finishes are

condenses onto surfaces, coating them

typically less than 6 microns (0.00024 in.)

with a high-gloss film of metal.

thick, with a metal film of less than

It is a means of coating many different

1 micron (0.000039 in.). For functional coatings, thicknesses of 10 to 30 microns

metal, with metal.There are no tooling

(0.00039-0.0012 in.) are producedusing

costs, and the process is controllable and

plasma vaporizing techniques, which can

build up film thickness indefinitely.

Quality

Related Processes

Speed

repeatable, making it suitable for coating

• High quality, high gloss and protective finish with similar characteristics to spray painted coatings

• Electroplating • Galvanizing • Spray painting

• Moderate cycle time (6 hours including spray painting)

mass produced items. Prototypes and

Outer frame also rotates

Coating thickness depends on the

chamber. The plume of vaporized metal

materials,including plastic, glass and

Workplece mounted onto rotating fixture, which in turn rotates on a spinning wheel

Vacuum chamber Vaporized metal disperses

everything from single prototypes to

TYPICAL APPLICATIONS

Electrodes

Wire spiral carriers

Vacuum metalizing is used equally for decorative and functional applications. Decorative uses include jewelry, sculptures, trophies, prototypes, kitchen utensils and architectural ironmongery. Coatings can be functional, providing electromagnetic interference (EMI) or

radio frequency (RF) shielding, improved

TECHNICAL DESCRIPTION The parts are first cleaned and coated

When the correct pressure is reached,

with a base coat by spray painting. The

an electrical discharge is passed through

base coat has 2 main functions; improving

the wire of aluminium (or other metal) by

surface finish and encouraging the metal

the electrodes. The combination of the

vapour to adhere to the workpiece. The workpieces are mounted onto

electric current and high vacuum cause the almost pure metal to vaporize in an

rotating holding fixtures (custom made

Instant. It bursts into a plume of metal

for each part), which are in turn rotated

vapour, which condenses on the relatively

reflection, an electrically conductive

on spinning wheels. The assembly

cool surface of the workplece. The

surface or a vapour barrier. Some typical

is suspended within a frame, which

condensing metal adheres to the base

products are torch and automotive light

also rotates. All in all, the parts are

coat on the parts In a thin, uniform layer.

wear resistance, heat deflection, light

reflectors, machine parts, metalized

being rotated around 3 parallel axes

pi asti c fil m s an d con sum er el ectron 1 cs.

simultaneously. This is to ensure an even coating with line-of-sight geometry.

RELATED PROCESSES

Before the vacuum metalizing can

The vacuum metalized film Is protected by the application of a topcoat. This Is water-clear, but can be coloured to mimic various metallic materials. The

Other processes used to coat materials

take place, a vacuum has to be generated

topcoat is then cured in a warm oven

with metal include electroplating (page

within the metalizing chamber. To reach

for 30 minutes or so. The end result Is

10' millibars (0.0000145 psi) takes

a metallic layer encapsulated between

approximately 30 minutes, depending

2 coats of lacquer, which is durable and

on the materials being coated. The

highly reflective.

364), galvanizing (page 368), and spray painting (page 350). Spray painting with conductive paints is also suitable for RF and EMI shielding,These processes are closely related; spray painting is used to apply abase coat pre-metalizing and seal in the delicate metal film with a topcoat. Spray painting and vacuum metalizing can coat the widest range of materials.

metalizing process can operate at a lesser

degree of vacuum, but the quality of the finish will be inferior.

Case Study

i

Vacuum metalizing brass hinges with aluminium The process starts with the application

(image 4). The whole assembly is loaded into

of a base coat lacquer (image i).This is

the vacuum chamber (image 5). It takes about

Everything that goes into the vacuum chamber emerges with a thin coating of

essential for a high-quality finish; not only

30 minutes or so to pull a sufficient vacuum.

vaporized metal. The unprotected metal

does it promote good adhesion between

An electrical discharge is passed through

film can be easily rubbed off at this stage.

the workpiece and metallic coating, it also

the wire, causing it to heat up and vaporize

Spraying a lacquer topcoat onto the

gives a smoother finish. Once applied, the

(image 6). It glows white-hot and a film of

workpiece secures the thin metallic film and

workpieces, which are mounted onto their

aluminium begins to form on the workpiece.

bonds it to the base coat. The parts before

jigs, are loaded into a warm oven to accelerate

The vacuum metalizing process takes only a

and after they have been vacuum metalized

the curing of the base coat (image 2).

few minutes. The chamber is brought back up

appear markedly different (image 7).

After 30 minutes or so, the jigs are loaded,

to atmospheric pressure and the door opened.

with the parts, onto the rotating holding fixtures (image 3). Loading the parts by hand means that they are individually checked, which limits waste. The parts are secured

to the holding fixtures by clips that will not affect the quality of the coating. Each design will require a different method for connecting it to the holding fixtures. The wire spiral holders that connect the positive and negative electrodes are loaded with 95% pure aluminium wire

QUALITY

smoother transition from prototyping

Vacuum metalizing is used to

to production, and also means that

increase the surface quality by

designers can explore the look and feel of

improving reflectivity, wear and

their objects in metal at an early stage.

corrosion resistance. It also improves

The coating produced by vacuum

colouring capability; the topcoat can

metalizing is fine and uniform. Passing

be impregnated with a wide range of metallic colours.The quality of the finish

the workpiece through the process more

Is determined by the quality of the

than once Increases the film thickness. Vivid colours can be used to replicate anodized aluminium, bright chrome,

by the vacuum chamber, but also by the

COSTS

silver, gold, copper or gunmetal, among

geometry of the part. Flat parts up to

There are no tooling costs, but jigs

products by increasing their resistance to

geometry.This means that the parts

others.The advantage of this is that

1.2 m x i m (3.94 x 3.3 ft) can be coated,

often have to be made to support the

corrosion and wear. Very little material

have to be rotated during metalizing to

relatively Inexpensive materials can be

where as 3D parts are limited to

workpiece in the vacuum chamber.

is needed for the metal coating because

surface priorto coating. The coating is applied on line-of-sight

encourage an even coating, and deep

formed and then vacuum metalizedto

1.2 m x 0.5 m (3.94 x 1.6 ft) because they

undercuts and recesses can escape the

give the look and feel of metal.

have to rotate as they are metalized.

Cycle time is moderate (up to 6 hours).

it is generally a very thin film, but this

It is quite a labour intensive process;

depends on the application.

the parts have to be sprayed, loaded,

coating process.The vacuum can be replaced with argon gas to encourage a

Metalizing extends the life of

DESIGN CONSIDERATIONS

COMPATIBLE MATERIALS

unloaded and sprayed again.This means

more vigorous coating, but this will be

The quality of the coating 1s affected by

Many materials are suitable, including

the labour costs can be quite high, but

more expensive to carry out because it is

the surface quality of the workpiece. In

metals, rigid and flexible plastics, resins,

depend on the complexity and quantity

a specialist process.

other words, the metal finish will only be

composites, ceramics and glass. Natural

of parts.

as smooth as the uncoated finish. If the

fibres are not suitable; it is very difficult

DESIGN OPPORTUNITIES

desired effect is distressed, this must be

to apply vacuum if moisture is present.

Vacuum metalizing is an inexpensive

achieved priorto metal coating.

and versatile metal coating technique.

The maximum size of the part that

There Is no tooling cost, which makes a

can be metalized is determined not only

Aluminium is the most commonly

ENVIRONMENTAL IMPACTS Featured Manufacturer

This process creates very little waste.

used metal for coating. Other metals that

Spraying the base coat and topcoat has

can be used include silver and copper.

Impacts equivalent to spray painting.

VMC Limited www.vmclimited.co.uk

Mechanical Grinding, Sanding and Polishing Techniques Wheel cutting

Belt sanding Table Workpiece

Rotating platen

Honing

Abrasive coating

Spinning axle

Workpiece

Finishing Technology

Grinding, Sanding and Polishing Workpiece

Surface cutting

Profiled honing stone Outside diameter

Surfaces are eroded by abrasive particles In these mechanical processes. The surface finish ranges from coarse to mirror,

and can be a uniform texture or patterned depending on the

INTRODUCTION Grinding, sanding and polishing cover

Abrasive coating

Abrasive Workpiece

a wide range of processes used to finish

Support plate

metal, wood, plastic, ceramic and glass products.The size andtype of abrasive

technique used and type and size of abrasive particle.

particle, combined with the method of finishing, will determine the range

Hollow Profiled workpiece honing stone

Costs

Typical Applications

Suitability

These terms are used to describe

• No tooling costs for many applications • Non-standard profiles may require tooling • Unit costs dependent on surface finish

• Automotive, architectural and aerospace • Cookware, kitchens, sanitary and medical • Glass lenses, storage jars and containers

• One-off to mass production

different techniques for surface cutting.

Quality • High quality finish that can be accurate to within fractions of a micron (0.000039 in.)

Related Processes • Abrasive blasting • Electropolishing

Lapping

Speed • Rapid to long cycle time, depending on size and type of finish

Abrasive 1 block

¦

1 Workpiece

fulfils a range of functions, including deburring metals, preparing surfaces forfurther processes, cutting into or right through materials, and precision

Cylindrical profile

finishes.There are many different

Abrasive pad Workpiece

grinding techniques, including wheel,

belt and platen grinding, honing and barrel finishing. Many different abrasive

Inside diameter

TECHNICAL DESCRIPTION

| Lap

Grinding is used to produce surface finishes on hard materials. The process

Linear

Edge cutting

of surface effects that can be achieved.

Table

materials are used, including metal, mineral, diamond and maize seed.

Sanding is used to describe the process of eroding surfaces with

abrasive-coated substrates.The abrasive

These are common techniques used for

They are not suitable for applying a

cutting surfaces in industrial applications.

super-bright finish. The diagrams

Each is capable of applying a range

Illustrate how they are set up to cut

of finishes, from super bright to very

different geometries of product. The

coarse, depending on the type of abrasive

rotary method is suitable for circular and

material. They all rely on lubrication,

Irregular tube and rod profiles; as the belt

which reduces the build up of heat and

spins, the platen rotates to produce an

wear on the cutting tool.

even finish around the outside diameter.

To achieve a highly reflective and super-bright finish, the material will pass through a series of stages of

of rotationally symmetrical parts. It Is

surface cutting, which will use gradually

a precise method of surface cutting;

finer grits of abrasive. The role of each

an example application Is finishing the

abrasive is to reduce the depth of surface

inside diameter of cylinder blocks in

undulation. In mirror polishing this Is

engines. The tooling for this can be made

measured in terms of Ra (roughness

up specially for each job. The abrasive

average); a mirror polish is less than Ra

surface wears away gradually as it is

0.05 microns (0.0000019 in.).

used, and therefore has to be replaced to

Wheel cutting is carried out at high

particles consist of sand, garnet,

speed. Either the outside edge or the

aluminium oxide or silicone carbide;

face of the wheel is coated with abrasive

each has its benefits and limitations.

The grade of paper (grit) is determined by the size of particle and ranges from 40 to 2,400. Lower numbers indicate fewer particles for the same area and so produce a courser finish. These processes are known as

Honing is suitable for grinding and polishing internal and outside diameters

retain accuracy.

Lapping is typically used to produce a very fine and super-bright finish on hard

particles, generally made from metal

metallic and glass surfaces. The abrasive

and so providing a hard surface to grind

Is not coated onto the pad or block, but

or polish. They are equally suitable for

is Integral to it. Blocks are rigid abrasive

coarse grinding and diamond polishing.

blocks, and pads are flexible rubbers

The set up of the wheel and table will

impregnated with abrasives of a defined

determine the precision of the finish. Belt sanding Is used in both woodworking and metalworking. There

grit size. The surface finish is therefore very controllable. Lapping can be carried

out at different speeds depending on the

polishing when they are used to produce a bright and lustrous finish on hard

are many different types of machine.

material being polished; mirror finishes

Including free standing and portable

on flat and cylindrical surfaces can take many hours to complete.

surfaces. Polishing is characterized by

types. Like wheel cutting machines, they

the use of compounds in the form of

operate at high speed and are designed

pastes, waxes and liquids in which the

to apply the desired finish very quickly.

Case Study

Case Study

Wheel grinding

Honing glass

Wheel grinding is used to produce a

in this case honing is being used by Dixon

perfectly into it (image 3). The glass stopper

very flat surface that is suitable for rapid

Glass to produce an airtight seal between

is finished in the same way.

prototyping onto using the direct metal

a glass container and a stopper.

laser sintering (DMLS) process (page 232).

The profiled metal honing stone is

The finished products (image 4) are used to store scientific specimens for

First the surface is milled to provide an

machined specially for this application.

many decades, and honed glass is the only

even surface for grinding (images 1 and 2).

It is loaded Into the chuck of a lathe and

material capable of this.

This speeds up the process.Then the

coated with a mineral based cutting

metal plate 1s placed onto the magnetic

compound (image 1). As the part is ground,

grinding table and carefully ground for

the coarseness of abrasive compound Is

up to 45 minutes to produce the desired

reduced to produce a finer finish (image 2).

Ra value (images 3 and 4).

Abrasive honing increases the size of hole very gradually until the glass stopper fits

Featured Manufacturer

CRDM www.crdm.co.uk

abrasive particles are suspended. Cloths

widespread and cover both Industrial

are commonly used to apply the abrasive

and DIY projects.

paste, elther by h and or spun at high speed on a wheel. Mixing water with abrasive-coated substrates, such as wet and dry paper,

Abrasive blasting (page 388) is

glass specimen jars (see case study) are

finish obtained with 80-100 grit will

ground with a honing tool to form a

be Ra 2.5 microns (0.000098 In.); a dull

metal castings. It is a versatile and rapid

hermetic seal capable of maintaining

buffed finish from 180-220 grit will be Ra

into or right through fibre reinforced

process, but produces a limited range of

the contents for more than icq years.

composites, metals and glass.This is

surface finishes, all of which are matt.

Mechanical polishing produces

especially useful for brittle materials.

Polishing and grinding of embossed patterns in metal will emphasize the

hygienic surfaces, suitable for catering

As well as finishing, grinding can cut

produces a similar effect.The water suspends abrasive particles that form

RELATED PROCESSES

during sanding, creating a paste that

Electropolishing (page 384) Is used to

commonly used to smooth and finish

depth of texture.

and medical applications. Polished metal finishes reflect over

1.25 microns (0.000049 i1"1-); dull polish from 240 grit will be Ra 0.6 microns

(0.000024 in.); and a bright polish produced with a polishing compound will be Ra 0.05 microns (0.0000019 in-)-

QUALITY

95% of the light that hits their surface. Finely polished stainless steel Is i of the

finishes on metal. It is not as accurate as

It is possible to grind and polish surfaces

most reflective metals and can be used

Polished surfaces are more hygienic

TYPICAL APPLICATIONS

these techniques and cannot produce

accurate to within fractions of a micron.

as a mirror.

and easier to clean, which makes them

contributes to a very fine surface finish.

produce bright, lustrous and burr-free

DESIGN OPPORTUNITIES

These processes are used in all

such a bright fin1 sh. The advantage of

Precision operations are considerably

Depth of surface texture at this scale

very suitable for high traffic areas and

manufacturing Industries both for

electropolishing is that part geometry Is

more expensive and time consuming,

is measured as a value of Ra (roughness

human contact. In contrast, satin and

surface preparation and as precise

not a significant consideration and will

but are sometimes the only viable

average). Approximate Ra values for

finely textured finishes are prone to

finishing operations. Applications are

not affect cost or cycle time.

method of manufacture. For example,

Featured Manufacturer Dixon Glass www.dixonglass.co.uk

metal finishes are as follows: a ground

fingerprints and other marks.

Case Study

Case Study

^ Rotary sanding

-> Vibratory finishing

This is a typical application for the

This is a method used for finishing high

rotary belt sanding method (image i).

volumes. It is especially suitable for deburring

is used to produce a very fine finish on

Crushed maize seed (image 2), which

It produces an even satin finish on the

metal, but is also used to cut back painted

hard surfaces, is the next stage in the

surface of stainless steel (image 2). It is

surfaces and a range of other applications.

abrasive process.

equally suitable for non-uniform profiles.

A deep drawn (page 88) metal part is placed into the vibrating barrel, which is filled with smooth, hard pellets (image 1). It works in much the same way as pebbles eroding

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each other on the beach to produce smooth,

33

rounded stones. Many products can be in the barrel together.

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1 J D ¦) 1 1 ") 1 •)

desirable results.The hardness of the

material will affect how well It finishes, as well as how long It will take.

I

COSTS Much grinding, sanding and polishing

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Case Study

cn 3;

^ Manual polishing This is the most expensive and time-

The final stage is a buffing process,

consuming method of polishing. It is used

which uses the finest polishing compound

can be carried out with standard tooling.

to produce an extremely high surface

to produce a highly reflective finish. It is a

Consumables are a consideration for the

finish on the surface of parts that cannot

labour intensive process, but is nonetheless

unit price. Specific tooling can be very

be polished by mechanical means. This

used to finish a high volume of products

costly, but depends on the size.

polishing method can be used to work every

(image 4).

Cycle time is largely dependent on

surface of this colander (images 1-3). The

Featured Manufacturer

the size, complexity and smoothness of

size of spinning mop can be adjusted to fit

Plpecraft

surface finish. Brightly polished surfaces

smaller profiles such as spoons.The density

www.pipecraft.co.uk

can take many hours to achieve.

of the mop is adjusted for different grades

Labour costs are also dependent on

of cutting compound.

the size, complexity and smoothness

Repeating patterns can be polished into surfaces, like those found on cafe tables,These patterns reduce the visual effects of wear and dirt.

It is often more cost effective to polish stock material, such as sheet or tube, prior to fabrication. The joints can then be polished manually afterwards.

and rely on either rotating or moving back and forth. In contrast, cosmetic grinding and

of surface finish required. A dull polish will add about 10% of the raw material cost, a measured finish about 25% and a reflective finish about 60%.

polishing operations can be applied to most shapes because they can be carried out manually If necessary.

The hardness of the material will affect the surface finish. Stainless steel Is

ENVIRONMENTAL IMPACTS Even though these are reductive processes, there is very little waste produced in operation.

very hard and so can be polished to a very

DESIGN CONSIDERATIONS

fine surface finish; aluminium is a softer

The shape of the part will determine

metal and so cannot be polished to such

the effectiveness of these processes.

a bright lustre.

For example, precision grinding and

polishing operations are limited to flat,

COMPATIBLE MATERIALS

Featured Manufacturer

cylindrical and conical shapes.This is

Any material can be ground, sanded

Alessi

because the operations are reciprocal

or polished, but they may not produce

www.alessi.com

Case Study

Case Study

-> Lapping

-> Diamond wheel polishing Diamond particles are used to finish a range

The diamond cutting wheel is spinning at

Lapping is used to produce a range of

of materials that are too hard for other

high speed and produces a super fine finish

finishes, including reciprocal patterns, dull

polishing compounds.They are also used

in amatter of seconds (rmages 2 and 3). This

and super bright finishes. To polish a sheet of

prior to polishing (image 3) because a

for high speed finishing of plastics. This

is a mass-production method suitable

stainless steel to a bright finish, the polishing

protective plastic film is applied by the

acrylic box has been CNC machined. The

for finishing a high volume of products

compound is applied with a roller each time

machine directly after polishing. The

lid and base are paired up and then the 4

(image 4).

the lapping pad passes over the surface

circular pads that make the pattern

sides are cut on a circular saw (image i).This

(image i). Pressure is applied to maintain

(image 4) are impregnated with abrasive

produces an accurate finish, but it has an

a very accurate finish. Afterwards a lime

particles. The pattern (image 5) is a

undesirable texture. The workpiece is placed

substitute is spread over the surface of the

typical example of the finish that can be

stainless to remove any remaining moisture

achieved by this method.

on the cutting table and clamped in place.

When lapping to produce a patterned finish, the edges of the sheet are deburred



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Featured Manufacturer

Featured Manufacturer

Zone Creations

Professional Polishing

www.zone-creations.co.uk

www.professionalpoUshing.co.uk

TECHNICAL DESCRIPTION

Electropolishing Process

The electropolishing process is made up of 3 elements: the pre-cleaning (where

necessary), the polishing (see diagram) and the final cleaning to remove

Finishing Technology

chemical contaminants.

Electropolishing

The process takes place in a bath of electropolishing solution, which is made up of phosphoric and sulphuric acid. The

This is the reverse of electroplating; material is removed from the surface of the workpiece by electrochemical action to leave

bath is maintained between 50°C and

INTRODUCTION

90°C (122-194°F), depending on the rate

Electropolishing produces a bright

Electrically charged workpiece (+)

lustre on the surface of metals. It is an

more rapid the reaction. The workpiece

electrochemical process; surface removal

metal parts with a bright and clean finish.

is suspended on an electrically charged

takes place in an electrolytic solution, which can be very accurate. As well as deburrs, passivates and improves the

• No tooling costs, but jigs are required • Low unit cost (roughly 5% material cost)

Dissolved metal particles

jig and becomes the anode. The cathode

Heated electrolytic solution (phosphoric and sulphuric acid)

solution and is generally made of

is also placed in the electropolishing

polishing, this process cleans, degreases,

Costs

of reaction; the warmer the solution, the

the same material as the workpiece.

Typical Applications

Suitability

corrosion resistance of metal surfaces.

For electroplating, conversely, the

• Architectural and construction • Food processing and storage • Pharmaceutical and hospitals

• One-off to mass production

It is becoming more widely used because

workpiece becomes the cathode.

the environmental impacts are less

Microscopic detail

harmful than those of other processes. Quality

Related Processes

Speed

• High quality, bright, lustrous and hygienic surface finish

• Electroplating • Grinding, sanding and polishing

• Moderate cycle time (5-30 minutes)

When an electric current is passed between the cathode and the workpiece,

the electropolishing solution dissolves

Electropolished stainless steel has similar visual characteristics to chrome-

metal particles from the surface of

plated metals. Electropolishing is a

the workpiece. Surface dissolution

takes place more rapidly on the peaks simpler process than electroplating

driven by industry's aim to reduce the

chrome (page 364) and uses less water

consumption of chrome and other heavy

and chemicals, so is more cost effective.

metals (very toxic chromic acid is used for

As a result of the increase in use of

chrome plating). Electropolishing does

electropolishing, it is steadily becoming

produce chemical waste that must be

less expensive.

because that is where the power density is greatest. Low points are dissolved more slowly, and thus the surface of the material is gradually made smoother.

After electropolishing the parts are neutralized, rinsed and cleaned.

cleaned and pH neutralized, but it is less harmful than these other processes.

TYPICAL APPLICATIONS

Similar to mechanical polishing (page

Electropolishing has become a widely

376), electropolishing is a reductive

accepted finishing process for metals.

process. However, it is possible to

In architectural and construction

electropolish complex shapes that would

metal work, it is used for both aesthetic

be impractical by mechanical means.

andfunctional reasons (resistance

surface finish prior to electropolishing

to corrosion and reduced stress

QUALITY

concentration). In the pharmaceutical

The quality of finish that can be achieved

greater than 50 microns (0.002 in.), so a

and food industries it is used for

with electropolishing enhances the

rough finish will be smoothedbut not

mainly functional reasons (hygiene

surface of metalwork both aesthetically

completely removed. Even so, this process

and resistance to corrosion). Aesthetic

and functionally. Aesthetically, it

is frequently used for deburring as well

applications make up roughly 90% of its

increases the brightness and reflective

as polishing because burrs are like high

total use.

index by smoothing (polishing) the

points and so are dissolved very rapidly.

RELATED PROCESSES

level, the high points are dissolved

produces a finish that is clean, hygienic,

Electropolishing has been steadily

more rapidly than the troughs.The

less prone to stress concentration

replacing more ecologically harmful

result is reduced surface roughness

and more resistant to corrosion. The

processes such as chrome plating

and reduced surface area. However, the

electrochemical action removes dirt,

(see electroplating, page 364).This is

end result is largely dependent on the

grease and other contamination.

surface of the metal. On a microscopic

because material removal is usually no

Functionally, electropolishing

Case Study

Electropolishing architectural steelwork This case study demonstrates a recent

and rinse the parts. They are mounted onto

development in electropolishing technology.

a rotating frame which suspends them in

The equipment has been modified to reduce

each tank (image 4),

effluents and improve the environmental credentials of the process.

Throughout the process test pieces are checked to measure the rate of

They are dipped in the electrolytic solution for 10 minutes or so. As they are raised up, the green acidic mixture drains

back into the tank (image 5), The polishing

electropolishing accurately (Image i).

process is complete, and the rest of the

Electropolishing is generally used to remove

process neutralizes and rinses.

up to 40 microns or so: this sample shows a reduction of 30 microns (0,0012 in,).

they have been rinsed (image 6), and are

The sample indicates the amount of time

then washed a final time to remove any

required in the electrolyte to remove

remaining contamination.The parts are

sufficient materials.

then heated to dry (image 7), after which

These are investment cast stainless

steel architectural spiders (see page 133),

3

The spiders are hung to drain after

they are safe to handle and so are packed and shipped.

which are designed to hold panes of glass in buildings (image 2), They are jigged with electrical contact (image 3),This particular process requires only a small number of

baths to electropolish effectively, neutralize 5

It produces a more hygienic surface

not apply any mechanical stress to parts

COMPATIBLE MATERIALS

ENVIRONMENTAL IMPACTS

because potential microscopic bacterial

and so can be used to deburr andfinlsh

Most metals can be electropollshed,

The environmental Impacts of this

and dirt traps are opened up to allow

delicate parts that are not suitable for

but this process is most widely used for

process are threefold. Firstly, it Is

more thorough sterilization,The process

mechanical polishing techniques.

stainless steels (particularly austenitlc

replacing the use of chrome-plated steel,

grades). Generally, an electropolishing

which is a harmful material due to the chemicals used in its production.

dissolves iron more readily than other

This process is also useful in the

metallic elements, and this phenomenon

preparation of parts that will be used

plant will be set up for a specific material

means that electropollshed stainless

in applications that require contact

because different materials cannot be

Electropolishing uses less harmful

steels have a chromium-rich layer on

between surfaces.This method of

polished together or even In the same

chemicals, needs less water and Is

the surface,This layer protects the steel

polishing deburrs and so reduces

electrolytic solution. Other metals

simpler to operate. Secondly, It increases

from corrosion because it reacts with

friction between mated surfaces such as

that can be treated in this way Include

the longevity of stainless steel because it

oxygen to form chromium oxide, which

threaded assemblies.

aluminium and copper.

increases the material's natural

reactive to atmospheric elements. As well

DESIGN CONSIDERATIONS

COSTS

this process removes material, rather than coating with an additional material,

passivates the surface and makes it less

protection against corrosion. And thirdly,

as protecting the steel, the chromium-

The level of finish is determined by the

There are no tooling costs, but jigs are

rich layer can be so bright that It also

quality of the metal surface prior to

required for electrical contact.

gives the Illusion of chrome plating,

electropolishing, so preparation is key. Marks from blunt tools on the forming

the amount of material removal and

DESIGN OPPORTUNITIES

or cutting machine, deep scratches and

cleanliness of the part.

The entire process takes place

other imperfections will not disappear

submerged in baths of solution, which

with electropolishing. Instead,they

partially automated, so labour costs are

consumption of chemicals represents

has many advantages over mechanical

may be emphasized by the enhanced

relatively low. It adds only 5% to the cost

only a small proportion of the overall

operations,The process is equally

surface finish. Metalwork that requires

of the base material, as opposed to metal

costs. They tend to be far less hazardous

effective on small technical and large

preparation, such as a casting, Is abrasive

plating, which can add up to 20%.

to the operator, and the resultant residue

structural parts. Size and complexity

blasted (page 388) to produce a uniform

1s more easily treated than with other

Firma-Chrome Ltd

have no bearing on cycle time. It does

surface finish that will respond well.

metal finishing processes.

www.firma-chrome.co.uk

Cycle time is rapid, but depends on

This process tends to be either fully or

so reduces material consumption and eliminates delamlnatlon and other associated problems.

Approximately 25% of the chemical solution is replaced annually.The

Featured Manufacturer

Finishing Technology

Abrasive Blasting This is a generic term used to describe the process of surface removal by fine particles of sand, metal, plastic or other abrasive materials, which are blown at high pressure against the surface of the workpiece and produce a finely textured finish.

Costs • No tooling costs, but masks may be required • Low to high unit cost

Typical Applications • Architectural glass • Decorative glassware • Shop fronts

Suitability • High volume removal of surface material • Low to medium volume fine finishing

Quality

Competing Processes

Speed

• Very fine details can be produced by skilled operators

• Chemical paint stripping • Photo etching • Polishing

• Rapid cycle time, but slowed down by masking, layering and carving

INTRODUCTION Abrasive blasting encompasses sand

QUALITY

blasting, dry etching, plastic media blasting (PMB), shot blasting and bead blasting. All ofthesehave 2

With manual operations the success

of this process is largely dependent

main functions. Firstly, they are used

details can be reproduced accurately.

on the skill of the operator. Very fine

to prepare a surface for secondary

Material removal is permanent, so care

operations by removing contaminants

must be taken to etch the surface of the

andapplying a fine texture that will aid

workpiece in a controlled fashion.

TECHNICAL DESCRIPTION This is a simple process that can be used

glass bead, metal grit, plastic media and

can be used to apply a decorative texture

DESIGN OPPORTUNITIES

to attain extremely sophisticated results

ground walnut and coconut shells.

to the surface of a part such as affecting

This is afast and effective way of

on many different materials. Abrasive

Sand is the most commonly used

the transparency of glass or applying

removing surface material.The various

blasting can be either pressure fed. or

because it is the most readily available

a pattern. Other functions include

grades and types of blasting media mean

siphon (suctionl fed. Both can be used

and versatile. Metal grit abrasives include

deburring, cutting and drilling.

that a range of textures and effects can

inside a sealed booth (glove box) or a

steel and aluminium oxide. Steel grit

be achieved, from a very fine texture

walk-in booth. Alternatively, blasting

is the most aggressive and is used to

glass and shop fronts. It is the process

(similar to that achieved with acid

apparatus can be used on-site or

create a rough texture on the surface

of sculpting the glass with 3D relief

etching), to a more rugged sand-blast

outdoors if the workpiece is very large or

of the workpiece. Aluminium oxide is

impractical to move. With all operations,

gentler and less durable, resulting in a

the steady stream of compressed air

softer texture. Glass beads are the least

generally operates at pressures between

abrasive and reserved for more delicate

5.51 bar and 8.62 bar (80-125 psi), except

materials. Plastic media are the most

surface addition processes. Secondly, they

Glass carving is used in architectural

patterns, with and without the use of

look.The depth of texture will affect the

masking (see image, page 484, above

level of transparency in clear materials

right).

by increasing light refraction.This quality can be used to enhance the visual depth

some specialized systems such as PMB.

expensive blast materials and require

which operate at 2.76 bar (iOpsij.

specialist equipment. They are much

TYPICAL APPLICATIONS

of an image, which will also be affected

Typical surface removal operations

by layers of colour in the workpiece.

include the deburring and preparation of metal surfaces for further finishing

effective. The abrasive material is

shapes, from round to angular, can be

DESIGN CONSIDERATIONS

forced through the blasting gun from a

selected to suit the application. Certain

operations and removing damaged or

Like spray painting (page 350), this

pressurized tank, attached by a flexible

natural materials, such as walnut shells,

weak material from a surface such as

process is limited by line-of-site

pipe. Siphon fed systems are more

will not affect glass or plated material.

rotten wood from sound wood or paint

geometry.This also means that erosion

versatile because they suck the blast

This can be useful if, for example, the

and rust from metal.

will not occur under the edges of the

material through a feed pipe, which is

operator only wants to erode the metal

mask, but rather perpendicular to it.

simply inserted into a container of blast

part of a product made up of metal

include glassware, signage, awards and

The abrasive material must be matched

material. Both processes are controlled

and glass.

medals and art installations.

to the workpiece and it is advisable

by 5 main variables: air pressure, nozzle

to test the abrasives, pressure and

diameter, distance from workpiece.

distance from workpiece prior to full

abrasive flow rate and type of abrasive.

Typical decorative applications

COMPETING PROCESSES CNC engraving (page 396),photo etching (page 392) and laser cutting (page 248)

production.Textures can act as dirt traps,

emphasizing fingerprints on glass for

are all used to produce similar effects

example; to reduce visual degradation

on glass and a range of other materials.

they are often encased in a laminate or a

Textured plastic films laminated onto

clear, protective coating.

glass sheet produce similar effects to

Pressure fed systems are the most

The choice of abrasive material is

softer than other blast materials and the

Wax resists are used for decorative applications. The abrasive materials cannot penetrate 'slippery' materials and bounce off. leaving the masked area

crucial and will be affected by many

untouched. Wax resists are produced

factors, which include the material being

from artwork that has been generated in

etched, the depth, grade and speed of cut

2-tone and are applied to the surface of

and economics. The abrasives are graded

the workpiece using an adhesive backing.

in much the same way as abrasive papers. The choice of materials includes sand.

Case Study

Decorative sand blasting The glass vesse] being decorated here was

The product is held in a glove box with

surface has been built up in layers, in that

designed by Peter Furlonger in 2005. It was

protective gloves. The operator (artist)

the top layer has been fired with a blowtorch

shaped by glassblowing (see page 152). For

carefully etches away the unprotected areas

to produce metallic effect, the layer

this project, sand blasting has been used to

of the workpiece with virgin aluminium

underneath is non-metallic and the base

decorate the surface of the workpiece with

oxide, ranging from 180 grit to 220 grit

layer Is clear glass.

a multilayered artwork.The same principle

(image 4). Once the first stage of etching Is

can be used to apply decorative patterns to

complete, specific areas of the wax resist are

for the second stage of the etching process

surfaces, except the wax resist is replaced

removed, and other delicate areas have their

(image 6). Finally the wax resist and all other

with masking.

protection reinforced (image 5). This will

masking is removed to ready the workpiece

enable the artist to create a multilayered

for cleaning and polishing (image 7).

Firstly, the artwork or pattern is translated onto a wax resist, either by hand

etched image. This technique is particularly

or by printing (image 1) and applied to the

effective on this product because the coloured

The product is returned to the booth

workpiece (image 2). Negative etching is used to describe the process of etching the image and leaving the background intact. This case study is an example of

positive etching because the image is left intact and the background is textured.

Once the wax resist has been applied,

i

the inside surface is masked to avoid damaging it with the abrasive (image 3).

COMPATIBLE MATERIALS This process is most effective for etching metal and glass surfaces, but can be used to prepare and finish most materials such as wood and some polymers.

COSTS There are no tooling costs. However, masks maybe required, the cost of which

Is affected by the complexity and size of the area to be abrasive blasted. Cycle time is good, but is slowed down by complex masking and multilayerlng.

Automation of simple tasks will greatly improve cycle time. For manual operation labour costs are

relatively high. for spray painting (page 350) and other

ENVIRONMENTAL IMPACTS The dust that is generated during

hazardous finishing processes. Working in a sealed booth means that

abrasive blasting can be hazardous.

the blast materials can be reclaimed

Booths and cabinets can be used

easily for re-use. Attaching a vacuum

to contain the dust that Is created,

system to the blast head makes It

otherwise breathing apparatus will be

possible to reclaim spent material for

required, much the same as those used

field stripping applications.

Featured Manufacturer The National Glass Centre www.nationalglasscentre.com

JSi

Photo Etching Process

m

Laminating roller applies film Metal workpiece

Film adheres to metal surface

Finishing Technology

Photo Etching

r

This is surface removal by chemical cutting. It has a similar appearance to abrasive blasting. The surface of the metal is masked with a resist film and unprotected areas are chemically dissolved in a uniform manner.

=5 Costs Low cost tooling Moderate to high unit costs

Quality • Prolonged exposure to chemical attack will cause undercutting

Typical Applications • Jewelry • Signage • Trophies and nameplates

INTRODUCTION Photo etching, also referred to as acid

Laser cutting (page 248), CNC engraving

etching and wet etching,is the process of surface removal by chemical dissolution.

(page 396) and abrasive blasting (page 388) are used to produce similar effects

This process is precise andlow cost.

in a wide range of materials. However,

Phototooling is printed acetate, which is

lasers and CNC engraving heat up the

inexpensive to replace.The accuracy of

workpiece and can cause distortion in

the etching is determined by the resist

thin materials.

Suitability

film, which protects areas of the sheet

• Prototype to mass production

that will remain unchanged. Surface removal is slow, typically

Competing Processes

Speed

• Abrasive blasting • CNC machining and engraving • Laser cutting and engraving

• Moderate cycle time, typically 50-100 microns (0.002-0.0039 in.] per pass (5 minutes)

COMPETING PROCESSES

QUALITY

UV light source

Phototooling

. Unexposed areas remain soft 1 Exposed film hardens

A major advantage of photochemical

50-100 microns (0.0020-0.0039 in.) in

machining is that it is less likely to cause

a 5 minute pass. Depths of 150 microns

distortion because there is no heat,

(0.0059 in ) are suitable for decorative

pressure or tool contact; the final shape

applications. Patterns, text and logos can

is free from manufacturing stresses.

be filled with colour.

Stage 1: Applying photosensitive resist

Stage 2: UV exposure

The chemical process does not affect

the ductility, hardness or grain of the

TYPICAL APPLICATIONS

metal structure. . Oscillating nozzles

Applications include signage, control panels, nameplates,plaques and

DESIGN OPPORTUNITIES

trophies. Photo etching is also employed

This process is suitable for prototyping

by jewellers and silversmiths for

and high volume production.Tooling

decorative effect.

costs are minimal; the negatives can be produced directly from CAD drawings,

XX2x

. Exposed film protects metal surface

Stage 3: Etching Metal dissolved by acid

graphic software or artwork and last for

Ferritic chloride etchant

many thousands of cycles. Small changes are inexpensive and adjustments can be made to the design, so this process is

TECHNICAL DESCRIPTION

suitable for experimentation and trials

The material Is meticulously prepared;

during the design process.

it Is essential that the metal workpiece

Both sides of the part are exposed to

is clean and grease free to ensure good

ensure that the resist on the reverse is

adhesion between the film and the metal

fully hardened and protective. The soft,

Lines, dots and areas of etching can be

filled with colour if the etch is more than 150 microns (0.0059 in-) deep. Very small details can be coloured independently such as patterns,logos, text and

halftone images (visible dot pattern). It is possible to etch multiple layers with repeated masking and processing; layers significantly increase cycle time. Thin sheet materials, up to i mm

and negative are exposed to UV light.

surface. In stage 1, the photosensitive

unexposed photosensitive resist film is

polymer film is applied by dip coating

chemically developed away. This exposes

(page 68) or, as here, hot roll laminating.

the areas of the metal to be etched.

The coating is applied to both sides of the

In stage 3, the metal sheet passes

workpiece because every surface will be

under a series of oscillating nozzles that

exposed to the chemical etching process.

apply the chemical etch. The oscillation

Phototooling (acetate negatives) are

ensures that plenty of oxygen is mixed

printed in advance from CAD or graphic

with the acid to accelerate the process.

software files or artwork. In stage 2, the

Finally, the protective polymer film is

(0.04 in.), can be cut as well as etched (see

negatives are applied to either side of

removed from the metalwork in a caustic

photochemical machining,page 244).

the workpiece and the workpiece, resist

soda mix to reveal the finished etching.

Case Study

Photo etching a stainless steel plaque This case study illustrates the entire etching

negative is secured to 1 side of the workpiece

is likely that the chemical etchant will have

sequence where graphics are applied to only

and placed in the light booth, where it is

attacked them during processing.

i side of the metalwork. The part is a building

exposed to ultraviolet light on both sides

plaque for the British Embassy in Beirut.

(image 5). Unexposed polymer film is washed

2-stage process and usually takes no longer

The final product is a combination of photo

off in a developing process (image 6). Close

than 30 minutes. The colour is mixed, using

etching and colour fill (image i).

Filling the etched areas with colour is a

inspection often reveals minor blemishes in

cellulose-based paints, and squeegeed over

the protective film, which can be touched up

the workpiece surface (image 11). Multiple

negative (image 2). Each negative can be

with a liquid chemical resist that dries onto

colours can be applied to very intricate

used for a single etching process or multiple

the film instantly (image 7).This is a time-

patterns, but this takes considerably longer.

etchings; there is very little wear and tear, so

consuming process but it ensures a high

Each colour will require 20 minutes drying

they can last a very long time. In preparation,

quality finish.

time. Finally, excess paint is polished off and

The process begins with a printed acetate

the metal workpiece is carefully cleaned in

The workpiece now passes through

a series of baths. The first bath contains 10%

the etching process, which takes up to

hydrochloric acid and degreases the metal,

20 minutes (image 8). The depth of the

which is then washed in mild detergent and

etch is checked, 150 microns (0.0059 in-) is

water (image 3). The surface of the metal is

sufficient for filling with colour (image 9).

dried with pressurized air.

The remaining polymer resist and

The process takes place in a dark room to

protect the photosensitive film. The polymer

the plaque is finished (image 12). 6

chemical etchant are cleaned off with a caustic soda mix and then finally with

film is applied to both sides of the metal

pure water (image 10). It is desirable to

sheet by hot roll laminating (image 4). The

trim the edges at this stage because it

the film and phototooling are free from

although different types of photo resist

ENVIRONMENTAL IMPACTS

photo chemical machining and etching,

dust and other contamination because

and etching chemical are required.

In operation, metal that is removed

are generally limited to sheet materials.

this is large enough to be visible on the

It is possible to etch very thick materials,

finished workpiece.

Chemical cutting processes, including

or 3D surfaces using a paste. The stencil

Lines and large areas of surface

from the workpiece is dissolved in the

COSTS

chemical etchant. However, offcuts and

Tooling costs are minimal.The only

other waste can be recycled. There are

is applied in the same way, but instead

material can be removed without

tooling required is a negative that can

very few rejects because it is a slow and

of passing the workpiece under a series

causing any stress to the workpiece.

be printed directly from data, graphics

controllable process.

of oscillating nozzles, a chemical paste is

applied, which has a similar effect,

software or artwork.

COMPATIBLE MATERIALS

Cycle time is moderate. Processing

Most metals can be photo etched,

multiple parts on the same sheet reduces

DESIGN CONSIDERATIONS

including stainless steel, mild steel,

cycle time considerably.

The intricacy of detail is limited only

aluminium, copper, brass, n 1 ckel, tin and

by the quality of the photosensitive

silver. Aluminium is the most rapidto

film. Very small details, down to

etch and stainless steel takes the longest.

0.15 mm (0.006 in.) in diameter, can be reproduced. Therefore, it is essential that

Glass, mirror, porcelain and ceramic are also suitable for photo etching,

Labour costs are moderate.

The chemical used to etch the metal is one-third ferric chloride. Caustic soda is used to remove spent protective film. Both of these chemicals are harmful and operators must wear protective clothing. Featured Manufacturer Mercury Engraving www.mengr.corn

TECHNICAL DESCRIPTION

CNC Engraving Process

The cutting speed is determined by the material and engraving tool. Tungsten is the most commonly used material Movement in x. y and z axes

Finishing Technology

CNC Engraving

for cutting tips. It can be re-sharpened and even re-shaped several times. It is not uncommon to cut a fresh

tool for each job, depending on the requirements of the design. Harder

A precise method for engraving 2D and 3D surfaces, CNC engraving is a high quality and repeatable process. Filling

CNC and laser technologies (page 248) are the 2 main methods used for

engravings with different colours and the use of clear materials

engraving.These processes have replaced

are effective ways to enhance design details.

engraving by hand with chisels or a pantograph; both of these methods are

Typical Applications 1 No tooling costs Moderate unit costs

Quality

• Control panels • Toolmaking and diemaking • Trophies, nameplates and signage

Competing Processes Laser cutting Photo etching Screen printing

materials, such as granite, will require

INTRODUCTION

diamond-coated cutting bits. Track and bellows

This is a 3-axis CNC ma'chine, with

Workpiece . Adhesive film .

Engraving tool

ZH

1 Tungsten (or other) cutting tip

all movement controlled by the track and bellows. The operating programme

engraves the design either in straight lines, or following the profile of the

still practised, but the labour costs are

design and creating a centrifugal

too high for them to compete. Another

pattern. The choice of cutting path depends on the shape of the engraving.

Suitability

important factor is that CNC and laser

• One-off to batch production

technology can be used to engrave a

minimum of 3 axes; x,y and z. Machines

speed of cut. Smaller cutting heads,

wi der ran g e of m ateri al s, in cludin g

operating on 3 axes are suitable for

which are often 0.3 mm (0.0012 in.) or

1 mm to 50 mm (0.04-1.97 in.) per

stainless steel andtitanium.

engraving flatworl 2003 Material: Wood Manufacture: Surface decoration created by wood eating insects

different types and new ones emerge all

Images, opposite, above right and below).

the time. Thermoplastics can be melted

The breakthrough was made possible

is an exceptionally strong fibre used in applications ranging from medical

and reprocessed, but their strength will

by the development of microcapsules

devices to bullet-proof armour.

be slightly reduced each time. Even so,

of dicyclopentadlene (DCPD) that acts as a healing agent with a wall thickness

WOOD

No product demonstrates this more

Wood is also made up of polymers: lignin,

cleverly than Table by insects (see image,

plastics do not break down rapidly in

As a natural material, wood is prone to attack by Insects, animals and disease.

landfill and are energy efficient to recycle,

that would rupture when the material

so new products are constantly emerging

began to crack, but not before. The

cellulose and hemicellulose. Lignin is a

above). In this case wood eating Insects

that make use of these properties (see

microcapsules release the healing

polymer composed of repeating and

were let loose on the table after it was

image, above left).Thermosetting

agent, which is catalyzed by chemicals

cross-linked phenylpropane units;

constructed.The patterns formed by

plastics, on the other hand,form polymer

also encapsulated in the material.The

cellulose is made up of repeating glucose

liquid material is drawn Into the crack by

molecules; and hemicellulose is a

the Insects are intriguing and will be different each time a product is made in

capillary action and polymerizes to form

complex branched polymer that forms

the same way.

a strong bond with the parent material.

cross-links between cellulose and lignin.

chains when 2 parts react together, or

(see composite laminating, page 206).

when i part is catalyzed.They differ

The rate of polymerization can be

from thermoplastics because during polymerization they form permanent cross-links, so cannot be heated, melted

andformed;they are shaped in a mold by pouring (see vacuum casting, page 40),

injecting (page 50), or vacuum drawing

adjusted to suit the process and application.This Is critical because the reactions are exothermic, so large wall

Self-healing plastic sample Made by: Beckman Institute, USA Notes: Image of a self-healing fracture specimen after testing. This shows

1 half of the specimen after it has been fractured into 2 pieces.

Wood has anisotropic properties

Up to 75% of material toughness Is

Some biopolymers, such as cellulose and

as aresult of its grain:both tensile

recovered by the self-healing process.

starch (page 446), can be molded and

and compression strength are greater

shaped in similar ways to thermoplastics.

along the grain than across it. Steam

bending (page 198) works by heating and softening the lignin into its plastic

Generally, the properties of families of

thicknesses may buildup too much heat during curing and affect the strength of

materials are similar.There are obviously

Unlike synthetic plastics, they will break

the part.

exceptions to the rule, and among the

down naturally and over a shorter time.

Violin Made by:

Frederick Phelps

Material:

Spruce

Manufacture:

Hand carved from solid wood

Notes:

Knot-free and very high quality spruce is still unsurpassed as a material for making violins.

These materials are relatively high cost compared to the other groups, so nowadays are generally only used when no others are suitable. For example, clear or tinted glass is used in reusable

packaging applications because it is inert and can be cleaned, sterilized, reused or recycled. Refractory ceramics used

for investment casting have very high temperature resistance, but are brittle enough to be broken away afterwards

without damaging the metal part within.

COMPOSITES Composites combine the properties of

different material groups and so blur the boundaries between them. The Glass bottles

and the metal melts varies according to

bulk shapes in arange of metals.The

most readily combined materials are

Made by: Beatson Clark Material: Soda lime glass

its ingredients. Low melting point metals,

hammering or pressing action forces the

plastics with fibre reinforcement.The

such as zinc (42ocC/7880F), become liquid at a temperature that is below the point

metals into shape; as a result the grain

type of plastic determines the method of

follows the contours of the part. Liquid

forming. Fibre reinforcement is selected to suit the performance demands of

Manufacture: Glassblowing (machine blow

and blow) Notes: Clear glass cannot tolerate colour contamination, but brown or green glass can use a high percentage of

mixed cullet (recycled glass).

of degradation of some thermosetting

state forming produces turbulence in the

plastics.They can therefore be shaped

hot metal, and so the resulting part has

the application and has a similar effect

in a plastic mold (page 144), which has

inferior mechanical properties.

to grain in wood, producing materials

obvious financial advantages. Metals

with anisotropic properties. Processes

with a higher melting point can be cast

CERAMICS AND GLASS

such as 3D thermal laminating (page

in molds made from steel. However, steel

Ceramics are made up of non-metallic

they have the potential to replace the conventional materials for any given

violin; maple (page 475) isusedforthe back; and the neck, bridge and tuning

application. Plastics are making the

buttons are carved from rosewood or

biggest impact by replacing metals

is formed into the direction of bend.

cast (page 130) in refractory ceramic

good high temperature properties, but

228),filament winding (page 222) and composite laminating (page 206) take advantage of this property because the fibres can be laid down according to the

The length of the grain also affects the

shells, or formed in their solid or plastic

this also means that a lot of energy is

direction of stress. Even injection molded

in critical applications. However, the

ebony (page 478).The finest violins are produced from wood that was felled

strength of wood. Processes that reduce

state. Unlike polymer chains, the strength

required during production. Ceramics

(page 50) fibre reinforced plastic parts

properties of some materials are

io or more years previously. The tree is felled in the winter months, when it is

state so that the wood can be shaped over aformer.This process utilizes wood's

and refractory metals cannot be cast in

substances and are formed at high

inherent strengths because the grain

this way and so are either investment

temperatures.Therefore, they have

grain length, such as CNC machining

of bond between metallic elements does

are either crystalline or non-crystalline.

have anisotropic properties because the

irreplaceable. High quality acoustic

(page 182), therefore reduce tensile and

not decrease overtime or with repeated

Crystalline ceramics, known simply as

fibres align with the direction of flow.

musical instruments, such as violas,

said to be 'sleeping', so that there is as

recycling.This is of great importance

ceramics, can be shaped by hand (page

little oil and moisture in the wood as

because the process of mining metals

Finite Element Analysis (FEA) software is employed to maximize the efficiency of fibre reinforcement whilst minimizing

violins and cellos, are still hand crafted

by highly skilled makers. Every aspect

possible.These instruments are worth a

of the product from material selection

lot of money, but the harmony that has

molding issues.

to tuning is overseen by the maker

been struck between the materials and

(see image, above), and a signature

manufacturing remains unchallenged by

on the finished piece represents their

modern methods.

compressive strength.

METALS

is more expensive and energy intensive

168), pressing (page 176), slip casting (page 172) or sintering, and are then

Metals are made up of metallic elements,

than the synthesis of plastics.

fired at high temperature in a kiln. Non¬

which are combined in different

When formed in their plastic state,

crystalline ceramics, known as glass,

amounts to form metals with specific

metals have improved grain alignment

are formed in their hot, molten state by

TRADITIONAL AND NEW MATERIALS

properties.The temperature at which the

compared with liquid state formed parts.

hand (page 160), blowing (page 152), press

Composite materials create new

dedication.Traditionally, spruce (page

bonds between the elements break down

Forging (page 114) is used to produce

molding, press bending or kiln forming.

opportunities for designers because

470) is used for the soundboard of a

Materials

Plastics There is an almost unlimited choice of plastics and rubbers; many

TYPES OF PLASTIC

thousands of different types surround us in our everyday lives.

chains of repeating units (monomers) which occur naturally. Synthetic plastics are produced by the petrochemical

Plastics are made up of polymers: long

They offer unique benefits for designers, manufacturers and

industry. Some natural polymers are

users. Certain types can outperform metals in many applications.

refined and molded without the addition of petrochemicals.These are known as

They are produced in large quantities to reduce cost, but we

bioplastics, and they include starch-

Foam swatches

based, cellulose-based and natural

chemicals. The formation of cross-links

still hold onto the values associated with natural materials.

rubber materials.

means that the curing process is i-way;

Material: Various -

they cannot be remolded.

Manufacture: Molded and cut

Therefore, over the years synthetic plastics have been engineered

produce as raw materials and are

Bioplastics require less energy to fully biodegradable at the end of

to look and feel like silk, leather and natural rubber.

Thermoplastics can be remolded

Made by: Beacons Products

Notes: Most plastics can be foamed with open or closed-cell structures. The

many times. Off cuts and scrap (regrind)

density, colour and hardness of

their useful life.There are also grades

can be reprocessed with virgin material

foam can be specified to suit the

of synthetic plastics available that have been modified to break down

without a significant effect on the

requirements of the application.

within a specified time period. This is made possible by the addition of

typically limited to less than 15%, but some materials may contain a much

ability to stretch and return to their

bioactive compounds, which do not

higher percentage.

original shape.Thermoplastic elastomers

affect the physical qualities of the

properties of the material. Regrind is

Thermoplastics are further

Elastomers are characterized by their

(TPE) can be melt processed in exactly the

plastic but enable it to be digested by

categorized by molecular structure and

same way as rigid thermoplastics.They

microorganisms in the ground within

are frequently over-molded and multi-

1 to syears. Products made with this

weight.The structure or crystallinity differs according to the type of material

material include some clear plastic

and method of manufacture. For

bottles, food trays and refuse bags.

example, if polyethylene terephthalate

Synthetic plastics are divided

(PET) is cooled quickly, the polymer

shot injection molded (page 50) onto rigid thermoplastic substrates to harness the qualities of both. Like synthetic plastics, synthetic

into 2 groups: thermoplastics and

chains form a random and amorphous

rubbers are produced by the petro¬

thermosetting plastics (thermosets).

structure. However, if it is allowed to

chemical industry. Natural rubber (NR),

The distinction is not always clear-cut

cool slowly, the polymer chains form an

on the other hand, is produced from a sap

because some materials can be both

orderly crystalline structure. Amorphous

tapped from the Para rubber tree [Hevea

thermoplastic and thermosetting

pi astics ten d to be tran sparent an d h ave

brasiliensis) and is used to make products

depending on their polymeric structure,

greater resistance to impact. In contrast,

such as lorry and aeroplane tyres.

for instance, polyester and polyurethane.

crystalline materials tend to have better

Materials can also be compounded to

resistance to chemicals.

produce composites of both groups.

Polymers are blended together to

Most types ofplastic can be foamed.

This is carried out with a blowing agent. There are many different types of foam,

The defining difference between these

form copolymers and terpolymers

ranging from flexible to rigid, with

2 groups is that thermosetting plastics

such as styrene acrylonitrile (SAN) and acrylonitrile butadiene styrene (ABS).

above). Foams are used for a spectrum of

form permanent cross-links between the polymer chains.This creates a more

All 3 groups ofplastic-bioplastics,

either open or closed cells (see image, applications such as upholstery, safety,

durable molecular structure that is

thermoplastics and thermosets -

model making and as a core material in

generally more resistant to heat and

contain elastomeric (rubber) materials.

composite laminating (page 206).

XI

o o c o

*

Pantone swatches

E-glass fibre reinforcement

Made by: Pantone

Made by: Various

Carbon fibre is manufactured by Material: Woven glass fibre

oxidizing, stretching and heating a

Manufacture: Injection molded

Manufacture: Extruded and woven

polymer, such as polyacrylonitrile

Notes: International reference used to

Notes: E-glass, or electrical grade glass.

Material: Polycarbonate (PC)

select, specify and match colours.

is borosilicate and was first

(PAN),to overi5000C (2732^) in a

made for electrical insulation. The

controlled atmosphere. The process of

type of weave used is determined

carbonization takes places over several

by the application.

stages of heating and so requires a great deal of energy. Eventually, long ribbons of

ADDITIVES, FILLERS AND REINFORCEMENT

plastics include metallic, pearlescent,

almost pure graphite are formed, and the

NOTES ON MANUFACTURING

therefore more suitable for thin wall

thermochromatic, photochromatic and

width of ribbon will affect the strength

Plastics with different molecular

sections and complex features.

Additives and fillers are used to enhance

photoluminescent.

of the carbon fibre.There are different

structures lend themselves to different

grades (strengths) of carbon fibre, which

m ethods of m anufacture. Th ermopl astics

all thermoplastics are compatible. Care

depend on the manufacturer.

are shaped by heating them until they

must be taken when using processes

the properties of plastics. They are used to improve colour, specific mechanical

Fillers to improve mechanical properties include talc, minerals, fibres

Due to their different properties, not

properties, electrical conductivity,mold

and textiles.Thermoplastics can be

Carbon fibre has very high strength to

are soft or liquid enough to be formed, so

such as multi-shot injection molding and

flow and antimicrobial properties and to

injection molded (page 50), extruded

weight and as a result of its own success

they are generally supplied in granulated

plastics welding to ensure a strong inter-

increase the material's resistance to fire,

and compression molded (page 44) with

is becoming more difficult to purchase

form. Processes such as thermoforming

material bond. Material incompatibility

UV light and chemical attack.

all of these fillers. Fibre reinforcement

because production cannot keep up with

(p§ge 30) require sheet materials, which

is sometimes used as an advantage, for

may be less than 1 mm (0.004 i11) 'or|g

demand. It is a relatively expensive

are extruded from granules.This

example, in release agents and lubricants.

Some plastics, such as polycarbonate

Stacking stool Designer: Rob Thqmpson

Date: 2001 Material: Polyester and glass fibre Manufacture: Composite laminating

acetate (CA) andpolylactic acid (PLA) are

(PC), polystyrene (PS) and PET, are water

in thermoplastic molding. Long and

material, but is becoming more

increases the material costs due to the

clear and so take colour very well; they

continuous strand fibre reinforcement

widespread in consumer products such

extra processing that is required.

Some are engineered to cure at room

thermoplastics. For example, Potatopak

can be tinted or opaque.The colours

is incorporated into thermosets by

as sports equipment.This is partly due to

Thermoplastics are also available as

temperature such as polyester, vinyl ester,

are typically made up of a carrier resin

compression molding, composite

the added value that carbon fibre brings

drawn fibres and blown film.

food packaging (see image, page 446 top right) is produced by compression

coated in pigment, which is added to the

laminating and 3D thermal laminating

to an application, but also as a result of

epoxy (EP) andpolyurethane (PUR);these are supplied in liquid form and mixed

Different amounts of crystallinity

Thermosets are cured in the mold.

processed using similar techniques to

molding powdered starch.

(page 228).The types of fibre used

improved manufacturing techniques,

also affect processing. For example,

with a catalyst or hardener. They can be

include glass (see image, above right),

including recent breakthroughs in

amorphous materials do not have a

poured or injected into a mold.

MATERIAL DEVELOPMENTS

reference to either Pantone (see image,

aramid, carbon and more recently hemp

recycling methods.Traditional composite

sharp melting point like crystalline

Alternatively, powdered, liquid or solid

The plastics industry is constantly

above left) or RAL.These are recognized

and jute. Fibre reinforced composite

materials.Therefore, they are more

thermosets are heated in a mold to

evolving. New blends, compounds and

as international standards and ensure

materials have superior strength for

laminating requires a great deal of highly skilled labour and is therefore very

suited to processes like thermoforming,

trigger the formation of cross-links.

additives are being developed to create

raw material during processing.

Colour is generally determined by

th at th e col our th at is specifi ed by th e

their weight, several times greater

expensive. New techniques are now

because the material stays soft and

designer in i country is exactly the same

than metal, and different grades are

being used, such as resin transfer

formable over a wider temperature

as the colour that is injection molded

molding and resin infusion (page 206),

range. In contrast, crystalline materials

by a factory in another country. Other

suitable for everything from boat hulls to lightweight stacking furniture (see

which are more rapid and mechanized

colour effects that can be achieved in

image, opposite).

and so reduce labour costs considerably.

will flow more easily in the mold due to their sharp melting point and are

The production of bioplastics crosses

opportunities, improve performance and

over with both thermoplastics and thermosets; they can be molded with

reduce cost. Many developments will

thermoplastic technology, but the

yeanbelowis abrief outline of some of

process may not be repeatable. Cellulose

the most important.

affect the design industry in the coming

/

Flexible active matrix display Made by: Plastic Logic Material: Plastic display using E Ink® Imaging Film Manufacture: Active-matrix LCD backplane fabricated onto plastic substrate Notes: Displays made from plastic are

more flexible and lighter than those made of glass.

L'Oreal shop, Paris development, and at present there are

Client: L'Oreal

very few commercial applications.

Date: Completed 2004 Material: Bencore Starlight polycarbonate

(PC)

ENVIRONMENTAL IMPACTS

Manufacture: CNC machining

There have been many developments that reduce the environmental impacts of plastics. For example, many disposable products are produced in bioplastics or a

There are many different types of

Bencore Starlight and Lightben

Printed circuitry is used in Plastic

lightweight composite plastic panels.

Made by: Bencore

Logic's flexible active-matrix display

Core materials include aluminium

Material: Polycarbonate [PCI

(see image, opposite above left).

honeycomb, DuPont™ Nomex®

Manufacture: High pressure laminated

honeycomb and corrugated and rigid foam. Bencore, an Italian manufacturer, produce a range of plastic panels used

Notes: Available in polycarbonate (PC), styrene acrylonitrile (SANI, high impact polystyrene 1HIPSI and polyethylene terphthalate modified

with glycol (PETG).

This technology has the potential to

thermoplastic with bioactive additives. Thermoplastics are very efficient to recycle.There is minimal degradation of quality and some products are even

Recycled plastic sheets Made by: Smile Plastics Material: 100% recycled thermoplastic Manufacture: Compression molded Notes: Many thermoplastics can be

revolutionize the way we read books,

made from 100% recycled materials.

preprocessed in this way, including

reports and even the morning paper.

Smile Plastics in the UK manufacture

polyethylene (PE). PET, PVC and polycarbonate (PC).

The rigid glass backpane required for

a range of plastic sheets by made up

in applications such as furniture, trade

conventional amorphous silicon-based

of ioo% recycled plastic material (see

fair stands, shop interiors and exteriors

image, above right).They are produced from packaging, footwear and even old mobile phones. Patagonia, an American

andmelamine contain formaldehyde;

based company, produce a range of

polyurethaneresin (PUR) contains

fleeces from 100% recycled plastics drink bottles (PET).The role of the designer is

diisocyanates; and polyvinyl chloride

(see images, above).The polycarbonate

available include epoxy resin,unfilled

displays has been replaced by a plastic, which means the display can be flexible,

(PC) core, whose commercial name is

nylon, and glass or carbon filled nylon.

thinner and more lightweight.

Birdwing®, is thermoformed into 19 mm

Traditionally these materials have been

(0.75 in.) diameter 3D cells.This core is

engineered to mimic production grade

Light emitting polymers, or polymer light emitting diodes (PLED), are based

laminated between clear or coloured PC

plastics such as acylonitrile butadeine

on the principles of electroluminescence.

sheets (see images, above).These panels

styrene (ABS), polypropylene (PP) and poly methyl methacrylate (PMMA) acrylic.

Sandwiched between 2 electrodes, the

to ensure that plastics can be recycled

are known pollutants and are toxic.

polymer lights up when an electrical

with minimal contamination.Therefore,

Some are referred to as volatile organic

parts shouldbe designed in a single material if possible and with recycling

are also available in styrene acrylonitrile

(SAN),high impact polystyrene (HIPS) or polyethyleneterephthalate modified

Recent developments have made it

current is passed through it. It is now

suitable for direct manufacturing low

with glycol (PETG).

volume parts and one offs as well as pre-

possible to print a matrix of plastics that emit different colours of light to produce

production models.

very thin flat panel displays.

Rapid prototyping (page 232) has revolutionized the design process. Not only are models accurate to within a few microns,but also this process is capable

of producing plastic parts that cannot be made in 1 piece in any other way. Plastics

Conductive polymers combine the

benefits of plastics technology with the

EAPs are similar to electroactive

and disassembly in mind. This book cannot avoid mentioning the negative environmental impacts

ceramics and shape memory metal

of certain plastics. Not only do they

conductivity of metals. Developments

alloys: they respond to electrical

take thousands of years to biodegrade,

include printed circuitry, light emitting plastics and electroactive polymers (EAP).

stimulation with a change in shape or

some are also harmful in production.

size.They are in the very early stages of

For example, polyester and epoxy

contain styrene; phenolic resin, urea

(PVC) contains dioxins.These chemicals

compounds (VOC) and are known carcinogens. During production care must betaken to avoid inhaling them, andsome plastics will continue to off-

gas during their lifetime and so both reduce indoor air quality and pollute the atmosphere.

POLYOLEFINS

Clamshell CD packaging Designer/client: Unknown Date: Unknown

Material: Polypropylene (PP) Manufacture: Injection molding

j^'ces DE CajK

V Polyolefins

POLYOLEFINS

POLYOLEFINS

IKEA Kalas mug

Delices de Cartier

• Polyethylene (PE) • Polypropylene (PP) • Ethylene vinyl acetate (EVA)

Material: Polypropylene |PP)

• lonomer resin

Manufacture: Injection molded

a

Designer/client: Monika Mulder/IKEA Date: 2005

PP and PE are the building blocks of the plastic industry and make up more than half of total global production.

Qualities:These plastics have alow

Made by/client: Alcan Packaging Beauty/Cartier Date:- 2006

Ni

Thin walled bottles

They have superior abrasion resistance

Applications: The whole family of

and tear strength, high levels of

materials are used to make textiles for

transparency and good compatibility and

consumer and industrial applications. PE

adhesion to many metals and polymers.

is used for thin walled plastic packaging.

with very high impact resistance. It was

their resistance to water absorption

developed in the igyos by DSM, who

Various

and attack by many acids and alkalis.

Made by: Material:

manufacture it underthe trade name

Manufacture:

They are non-toxic and are available as

Dyneema®. As a drawn fibre or sheet it is

Notes:

transparent, tinted or opaque. They are

up to 40% stronger than para-aramid

Extrusion blow molding (EBM) Polypropylene (PR), polyethylene (PE). polyethylene terephthalate

generally not suitable for applications

(DuPont™ Kevlar®, see polyamides page

above ioo0C (2i20F).

438) and 15 times stronger than steel. PP has exceptional fatigue resistance,

cap on a glass bottle Manufacture: Cap is injection molded

POLYOLEFINS

U H D P E i s an excepti on al m ateri al

coefficieTit of friction and are notedfor

PE has good resistance to punching

Material: DuPont™ Surlyn® ionomer resin

High density polyethylene (HDPE)

(PET) and polyvinyl chloride (PVC) are all suitable for EBM.

Their exceptional impact resistance

Examples include shopping bags, milk

makes them virtually shatterproof, even

bottles, medical and cosmetic packaging.

at low temperatures. lonomers can be shaped by

and tearing, even at low temperatures,

so is ideal for integral hinges and snap

POLYOLEFINS Plastic cork

It is non-toxic and so is used for toys and chopping boards. UHDPE is used for high performance

As a semi-rigid polymer it has similar

conventional thermal forming processes.

characteristics to LDPE. Increasing

As they cool and solidify the metal ions

applications such as bullet proof garments, ropes and parachute strings.

its properties are partly determined by

fits. It has a waxy feel, due to low surface

Made by:

Various

the vinyl acetate content increases

(sodium or zinc) form cross-links in the

its molecular weight, and it is classified

energy, which means it is difficult to coat

Material:

Ethylene vinyl acetate (EVA)

its flexibility and produces similar

thermoplastic structure, giving them

as high-density (H DPE), ultra high-

with adhesives and paints. Even so, it is

Manufacture:

Co-extrusion

itself to a wide range of applications. It is

easily welded and mechanically joined.

The plastic is tasteless, long lasting

similar characteristics to thermosetting

density (UHDPE),low-density (LDPE), ultra low-density (ULDPE) and linear low-density (LLDPE).

Notes:

characteristics to rubber.

plastics at low temperatures. On heating,

used for food packaging, drinking cups,

EVA can be semi-rigid, or very flexible, depending on the vinyl acetate content.

and can be extracted with a conventional corkscrew.

Atypical ionomeris ethylene

PP is a versatile material that lends

methacrylic acid (E/MAA). lonomers are

the ionic cross-links break down so the

caps and enclosures. Other uses include

thermoplastics with ionic cross-links.

material can be recycled and reprocessed.

furniture,lighting andwaterpipes.

STYRENES

MacBook Pro packaging

VINYLS Kolon Furniture 'Double Chair'

Made by: Unknown

Designer/ownenJan Konings and Jurgen Bey/

Material: Expanded polystyrene (EPS) Manufacture: EPS molding Notes: EPS is lightweight, protective and

Droog Design Date: 1997 Material: Polyvinyl chloride (PVC) covering and used furniture

insulating.

Manufacture: PVC covering stretched over used furniture to create new objects

STYRENES Attila can crusher Designer/client: Julian Brown/Rexite Date: 1996 Material: Glass filled acrylonitrile butadiene styrene (ABS) Manufacture: Injection molding

VINYLS Water soluble pouch

EVA is puncture and tear resistant and is often used for medical packaging such

Made by: Various

as blood transfusion bags. In recent years,

Material: Polyvinyl alcohol (PVOH) Manufacture: Plastic welded film

EVA has seen an explosion in consumer

Notes: The film dissolves in cold water to

and packaging applications such as

deliver a measured dose of

luxurious carrier bags and flexible net

detergent to laundry.

equipment, ear defenders and other safety equipment, children's toys and automotive parts.

SAN has high thermal stability and so

Vinyls • Polyvinyl chloride (PVC) • Polyvinyl alcohol (PVOH) PVC has a glossy appearance and its shore hardness can be adjusted to suit the application.

is often used for transparent kitchen

PVOH is a water soluble barrier film.

appliance mixing bowls, water purifiers

packaging used for glass bottles and

and other products that require a very

fruit. As foam it is used for trainer soles

high surface finish and durability combined with the convenience of

Qualities: PVC is along lasting material

Applications: GPPS is used for disposable

dishwashing. It is also used in the

andmore than half of global production

applications,from blown films and

food packaging, cutlery and drinking

automotive and medical industries.

is for use in the construction industry.

coatings to injection molded and blow

cups, CD 'jewel' cases, lighting diffusers

and imitation cork. lonomers are used in a range of

SBS and SEBS are used extensively

It has a glossy surface finish and is

molded parts. It is possible to mold thick

and model making kits. HIPS is used for

in multishot injection molding (page

available in a range of vivid colours. It is

wall sections without sink marks or voids.

vending cups, product housings and toys.

50) and co-extrusion applications with

either plasticized or not. Unplasticized

It is water-clear and so can feel and look

EPS is used in 3 main ways: either molded

thermoplastics including PE and PP

like glass and is therefore utilized in highinflates them into foam that is 2%

into the desired shape (packaging, .helmets and toys), molded into pellets (loose fill), or as sheet material that

PVC (uPVC) is rigid; where as plasticized PVC is flexible with a shore hardness

polycarbonate, page 435) and PA (see polyamide, page 438). Products include

material and 98% atmosphere.

can be cut (model making, thermal

babies'teats and dummies, ice cube

light, but PVC is not suitable for exposure

insulation and packaging), EPS is the

trays, soft touch grips and children's toys.

to prolonged periods at temperatures

end packaging such as cosmetics. Other

applications Include golf balls covers and

Styrenes

the soles of football boots. Costs; PE, PP and EVA are low cost, lonomers are medium cost.

• Polystyrene (PS) • Acrylonitrile butadiene styrene (ABS) • Styrene acrylonitrile (SAN) • Styrene butadiene styrene (SBS) • Styrene ethylene butylene styrene (SEBS) This is a broad range of thermoplastics that are easy to process and have good visual properties.

ABS has similar properties to HIPS with superior chemical and temperature resistance. It has a high gloss surface (like

GPPS) and is produced in vivid colours. SAN is resistant to impact and

scratching and has excellent light Qualities: PS is categorized as general

purpose (GPPS), expanded (EPS) and high impact (HIPS). GPPS is naturally

transmission qualities (90%). SBS and SEBS are copolymerized with

transparent andbrittle. HIPS is produced

synthetic rubber (page 445) and so have a large range of flexibility, with a shore

by blending PS with polybutadiene; it

hardness range of oA-soD.Theyremain

has improved impact resistance and

flexible even at low temperatures.

toughness. EPS is molded by expanding PS beads with gas and steam, which

These materials are generally limited

to applications below 8o0C (i760F).

(see polyolefins, page 430), ABS, PC (see

retardant and has good resistance to UV

above 6o0C (i400F).

ch eapest polymer foam.

ABS is used for a range of applications

range of 60-95A. It is naturally flame

Costs: Low.

The downside of PVC is that it

including housings for power tools,

contains chlorine and dioxins.This

telephones, computers and medical

has led to many campaigns against its

use, especially in food, medical and toy appli cati on s. H o we ver, th e producti on of PVC is increasing as it replaces more

wood and metal products in the building and construction industries.

Hydrolyzed polyvinyl acetate (PVA) makes PVOH, a water-soluble film. PVA is used in adhesives and coating because it

is not suitable for molding. PVOH is produced as fibres andfilms. It dissolves easily in water and the rate of dissolution

is adjusted by the structure of the polymer (crystallinity) and temperature; PVOH will absorb more water as it warms up. This means that PVOH can be used in water at room temperature without biodegrading; when the water is warmed to its trigger temperature, the polymer chains start breaking down rapidly. Applications: PVC is used to make 'vinyl' records. Now it is more widely used for extruded window frames, doorframes

and guttering. Other applications include identity and credit cards, medical packaging, tubing, hoses, electrical tape and electrically insulating products.

Vinyl is used to coat materials and fabrics to protect them from chemicals, stains and abrasion. Examples include

Acrylic and composites

ACRYLIC AND COMPOSITES Lymm Water Tower kitchen

• Poly methyl methacrylate (PMMA) Acrylic is used for its combination of clarity,

Designer/client: Ellis Williams Architects/

impact resistance, surface hardness and gloss.

Date; Completed 2005 Material: DuPont™ Corian® (acrylic and aluminium trihydratel

coated wallpaper and upholstery fabrics.

PVOH is used in hospital laundry

Russell and Jannette Harris

Manufacture: Thermcformed, CNC machined and

bags, water-soluble packaging,fishing

adhesive bonded

bait rigs and, when mixed with sodium

opposite) is a blend of PMMA and natural

ACRYLIC AND COMPOSITES

Discs showing edge glow

Polycarbonate

mineral (aluminium tri-hydrate).This

Made by: Various

• Polycarbonate (PC)

forms a hard, durable sheet material. It is

PC has excellent clarity and superior mechanical

relatively expensive, but has a luxurious

Material: Poly methyl methacrylate (PMMA) acrylic Manufacture: Cast or extruded

an ideal material for electronic products such as

quality unmatched in thermoplastics.

Notes: Tinted acrylic materials produce

mobile phones and Apple Mac computers.

Sheets are 3680 x 760 mm (145 x 30 in.),

properties. Rich and luminous colours make this

edge glow from ambient light.

6 mm to 12.3 mm (0.024-0.48 in.) thick

tetraborate, children's 'slime'.

Costs: Low.

DuPont™ Corian® (see image,

. and available in a wide range of colours. Qualities: Acrylic sheet materials are

heat the material above 8o°C (i760F),

available as extruded or cast.There are

because it will start to soften. It is an

Applications: Acrylic is used in point of

alternative to glass for certain products

small differences between the 2 that will

ideal material for laser cutting, scoring

sale displays,furniture, signage, light

such as beakers and spectacle lenses.

affect how they are machined and

and engraving (page 248) because the

diffusers, control panels, screens, lenses

It has an amorphous structure, which

formed. Sheets can be up to 60 mm

heat of the laser produces a gloss finish.

and architectural cladding.

contributes to it being the toughest clear

(2.36 in.) thick,but become very

Edge glow (see image, opposite) is caused by light picked up on the surface of the sheet and transmitted out through

Costs: Moderate.

expensive over io mm (0.4 in.). Sheet materials can be thermoformed (page

Qualities: PC is a suitable and safe

plastic. However, this also means that it

is prone to degradation by UV light and certain chemicals.

30), drape formed and machined (page 182). Acrylic can be machined to tight

the edges. Cut edges and scored lines

glow in the right lighting conditions.

such as ABS (see styrenes,page432),to

tolerances because it is a hard material

This effect is exploited in signage and

increase rigidity and impact resistance,

and it can be polished to a high gloss

decorative applications.

finish (especially by diamond polishing,

It is possible to incorporate materials

PC is blended with other polymers,

especially for thin walled parts. Blending and molding materials together

page 376). Sheet materials can be cut

and objects in cast acrylic sheet or blocks.

harnesses the desirable properties of

with conventional wood cutting

Examples included barbed wire, razor

each; PC-ABS is less expensive than PC

equipment, as long as the tool does not

blades, flowers, grass and broken glass.

and improves the properties of ABS, with

POLYCARBONATE Bluetooth Penelope*Phone Designer/clientr Nicolas Roope and Kam Young/

HuLger Ltd Date: 2005 Material: Polycarbonate (PC) Manufacture: Injection molded

THERMOPLASTIC POLYESTERS Sei water bottle Company: Sei Global Date: 2006 Material: Polyethylene terephthalate (PET)

x m 70

o "D > CO

Manufacture: Injection blow molded

i POLYCARBONATE

Miss K table lamp Designer/client: Philippe Starck/Flos Date: 2003 Material: Polycarbonate (PC) internal and external diffuser, and poly methyl

methacrylate (PMMA) acrylic frame Manufacture: Injection molded and vacuum

THERMOPLASTIC POLYURETHANE Feu D'lssey

Thermoplastic polyurethane

Designer/client: Curiosity Inc./Beaute Prestige

Thermoplastic polyesters

International

• Thermoplastic polyurethane (TPU) There is a range of flexibilities from shore hardness 55A to SOD. TPU is resistant to

Material: The red casing is thermoplastic

abrasion, tearing and puncturing.

Manufacture: Injection molded

Date: 2001 polyurethane (TPU1

metalized with aluminium

• Polyethylene terephthalate (PET) • Polyethylene terephthalate modified with

glycol (PETG) • Polybutylene terephthalate (PBT) • Polycyclohexylene dimethylene

this reduces the brittleness and premature ageing of PET. PETG has improved thermoforming properties and

so is ideal for lighting diffusers and medical packaging,for example.

PBT is electrically insulating and flame retardant. It can be glass filled,

terephthalate (PCT)

which improves its heat stability and

• Liquid crystal polymer (LCP) • Thermoplastic polyester elastomer (TPC-ET)

temperature range up to 2000C (3g20F).

better surface finish and processing, for

Qualities: The properties of TPU are

and weatherproof outdoor clothing. It is

There is a range of thermoplastic polyester

example. PC is a relatively compatible

similar to thermoset polyurethane (page

a tactile material and is used to make

engineering materials. All have high dimensional

material, which can be blended,

443).They are tough, durable, resistant

synthetic leather.

stability and are resistant to chemicals.

multishot injection molded (page

to fuels, oils and greases and resistant

50) and coextruded with a number of

to flexural fatigue across a broad

such as conveyor belts, automotive

fl am m abl e, h as excepti on ally 10 w m ol d

different materials.

temperature range,from -450C to 750C

interior linings, instrument panels,

shrinkage and very high dimensional

(-49 -167° F). Th ey exhibit 1 ow 1 e vel s of

wheels and over-molded gear sticks and

stability. LCP has rod-like molecules,

creep and high levels of resilience and so

levers. As well as molded products,TPU is

Applications: Applications include lighting diffusers (indoor, outdoor and automotive), police riot shields and

are suitabl e for 1 oad bearin g appl i cati on s. TPU is available as a resin, sheet, film

It is suitable for abrasive applications

THERMOPLASTIC POLYURETHANE

Golf ball

safety shields, beakers, beer glasses and

and tube. It is naturally opaque but can

Made by:

Various

babies bottles, motorcycle helmets and

be produced in clear.

Material:

Thermoplastic polyurethane (TPU) Injection molded Golf balls are made up of 2 or

Manufacture:

CDs and DVDs.

Notes:

Costs: Moderate.

applied as a coating. Costs: Moderate.

which align during melt processing.They

Qualities: PET is the most widely used

produce superior physical properties

thermoplastic polyester (for thermoset

over a wide temperature range with very

polyesters, see page 442). It can be

little thermal expansion or shrinkage,

amorphous or semi-crystalline

especially in the direction of flow;

depending on how it is processed and

the molecular alignment produces anisotropic properties.

more layersfthe core is typically

cooled (rapid cooling does not allow the

so is usedfor many clothing and

synthetic rubber and the outer

formation of a crystalline structure). It is

layer is TPU.

high temperatures and water absorption. LCP is an aromatic polyester. It is non-

Applications: TPU is breathable and sportswear applications such as shoes

PCT has all the mechanical properties of PET and PBT with greater resistance to

possible to modify PET with glycol (PETG):

TPC-ET is an engineering elastomer, it has excellent fatigue resistance and

ACETAL Flo-Torq® IV propeller hub Designer/client: Mercury Marine

Date: 2006 Material: DuPont™ Delrin® acetal Manufacture: Over-molded by injection molding onto titanium rods

THERMOPLASTIC POLYESTERS

THERMOPLASTIC POLYESTERS

Flexometer® wrist guard

Chevrolet HHR headlamp

POLYAMIDES

Polyamides

5^ Designer/client: Dr Marc-Herve Binet/Skimeter

Designer/client: DuPont™ Automotive/Chevrolet

• Polyamide (PA)

'/] Date: 2003

Date: 2006

• Aromatic polyamide (Kevlar® and Nomex®)

Material: Headlamp bezel and trim ring are

PA. commonly known as nylon, is a versatile

Material: DuPont™ Hytrel® thermoplastic polyester ITPC-ET) Manufacture: Injection molding

DuPont™ Crastin® polybutylene

material used in a wide range of applications.

terephthalate (PBT)

Aromatic polyamides are stronger than steel for

Manufacture: Injection moulded

their weight.

Makita Impact Driver Designer/client: Makita Date: 2006 Material: Polyamide (PA) nylon body and thermoplastic elastomer (TPE) pistol grip Manufacture: Multishot injection molded

as a substitute in garments, apparel and carpets. Following its conception in the

Acetal • Polyoxymethylene (POM)

1930s, nylon rapidly became a material in

POM, known as acetal, is an engineering polymer

its own right. Stockings and tights made

that bridges the gap between plastics and

out of nylon are very successful because

metals.

they are dramatically cheaper than silk versions. Cordura® is the trade name for nylon fabrics from Invista; they are tough, durable and resistant to abrasion.

Qualities: A high level of crystallinity

Qualities: There are many different

430), they are as close as scientists have

high impact strength, tear strength and

security, decoration, to reduce ultraviolet

grades of nylon, which are categorized

come to mimicking spider web.

impact resistance.

light and to preverft glass disintegrating

as follows: nylon 6; nylon 6,6; nylon 6,12;

if it breaks. It is a high performance

amorphous nylon (transparent) and high

their high heat performance, electrical

Applications: PET is used for drinks

material: Northsails jDLandBDr

temperature nylon.These grades can be

insulation andflame resistance.They do

material for ropes and sheets, and

to many chemicals, fuels and oils, and its

bottles because it is transparent in its

technology (page 228) laminates aramid

modified in a number of different ways

not have the same level of resistance to

commonly as fibre reinforcement in

low coefficient of friction reduces wear.

amorphous state, is easily blow molded

and carbon fibres between PET film.

to produce reinforced,flame retardant,

cutting and abrasion as para-aramids

composite materials. Meta-aramids

tough and super-tough versions.

and so they are often reinforced or

are foun d in appl icati on s th at dem an d

with low warpage, and has high fatigue

.laminated into papers.

very high performance such as power

endurance, so is suitable for spring and

its flexibility ranges from 30-80D. It has

used as a coating on glass and plastic for

and can withstand internal gas pressure from carbonated drinks. Post-consumer

PBT and PCT are used for oven handles and knobs, electrical connector blocks,

Nylon is self-lubricating,has alow

PET bottles are reprocessed into new

switches and light bulb housing. LCP is

coefficient of friction, and has good

products such as textiles andfleeces.

used for lighting connectors, computer

resistance to abrasion and chemicals.

PET is used as an industrial film. An

chip carriers, microwave oven parts

There are 2 main types of aromatic

Meta-aramids are used mainly for

Powdered nylon is fused into 3D forms

in rapid prototyping (page 232). Para-aramids are used as a single

means acetal is dimensionally stable at peak temperatures and can operate ¦close to its melting point. It is resistant

It is tough, even at low temperatures,

generation, aircraft, aerospace, racing

snap fits. It is ideally suited to injection

Applications: Nylon is used in bushes

cars and fire fighting. They are often

and bearings, electrical equipment

used as fabrics such as in flame resistant

molding (page 50) and machining (page 182), but can be rotation molded (page

undergarments worn by racing drivers.

36), blown (page 22) and extruded.

example is Madico's Lumisty view control

and cookware, mobile phone parts and

polyamides, including para-aramids

housings,furniture parts (mechanisms

film. The textured surface on the film

aerospace optical components.

known by the DuPont™ trademark name

and feet) and sports equipment.

TPC-ET is used in keypads, tubing,

Kevlar®, and meta-aramids, which are

As a drawn fibre, it exhibits similar

Costs: Nylon is moderate cost and

Applications: Acetal is used if the less

seals, sports goods, medical devices and

also known by the DuPont™ trademark

properties to silk and so is widely used

aromatic polyamides are high cost.

expensive thermoplastic polyester (page

soft touch handles.

name Nomex®.They are only available

refracts light and controls the viewing angle either horizontally or vertically. It is

Costs: Costs vary according to type: PET is

as spun fibre or sheet material because

437), PE (see polyolefins, page 430) and polyamides (opposite) are not suitable. It

there is no other practical way to form

is important in the appliance, hardware

low to moderate cost, TPC-ET is moderate

them. They have superior resistance to

and automotive, industries where it has

cost, PBT and PCT are moderate to high

temperatures up to 5OO0C (9320F) and

replaced metal parts. Uses include

cost and LCP is high cost.

are inherently flame retardant.

speaker grilles, sports goods, seatbelt

Para-aramidfibres have exceptional

systems and automotive fuel systems.

strength to weight, far superior to steel.

Alongside UHDPE (see polyolefms,page

Costs: Moderate to high.

They are non-flammable, resistant to

TPV and ETPV are made up of a thermoplastic matrix embedded with

Polyketone

stress cracking and fatigue, ultraviolet

• Polyetheretherketone (PEEK)

light and virtually all chemicals.They

PEEK is used for its hardness, dimensional

operate effectively at a wide temperature

particles of EPDM (see polyolefins,page 43 o). Th e th erm opl asti c m atri x of TPV

range from -2500Ct0 2500C (-418-482^).

is PP. It is known as ETPV when the PP

stability and wide working temperature range of -20oC to 250oC (-4-A820F|. It is suitable for molding and machining and is available as sheet, plate, rod and tube.

They can be formed by a host of melt processes including injection molding

is replaced by a higher performance thermoplastic.

(page 50), rotation molding (page 36) and extrusion, but they are very expensive

Applications: The range of applications

FORMALDEHYDE CONDENSATION RESINS

Qualities: PEEK is an opaque grey

and so often limited to coatings and

include keypads, soft touch handles and

Aramith billiard balls

material. It is non-flammable, electrically

linings.They can be transparent or

grips, hot water tubing, seals, gaskets,

insulating and hard, with a low friction

opaque, so coatings can appear invisible.

sportswear and goods, medical devices

Date: N/a

and automotive parts.

Material: Phenolic resin

coefficient. Mechanical properties are maintained at temperatures as high as

Applications: These are high cost

2500C (4820F), and it is resistant to many

materials, but they are effective as a thin

acids and chemicals.

PEEK reinforced with carbon fibre

Designer/client: Saluc

Manufacture: Molded, ground and polished

Costs: Moderate to high.

coating. Examples include non-stick cookware and self-cleaning coatings

has dramatically improved mech anical

on fabric and glass. Fluoropolymers are

properties with little increase in weight,

also used for automotive, aerospace and

Formaldehyde

Le Creuset casserole

and is used in the aerospace industry.

laboratory applications.

condensation resins

Designer/client: Le Creuset

Applications: Aerospace, medical

Costs: Very high.

FORMALDEHYDE CONDENSATION RESINS

Date: Unknown

equipment and electronic products.

• Phenol formaldehyde resin (PF) • Urea formaldehyde (UF) • Melamine formaldehyde (MF)

Material: Phenolic resin handle Manufacture: Compression molded

These thermosetting materials have a hard and glossy finish that is resistant to scratching.

Costs: Very high.

They are resistant to most chemicals, have good dielectric properties and operate across a wide

Fluropolymers • Polytetrafluoroethylene (PTFE) • Ethylene tetrafluoroethylene (ETFE) • Fluorinated ethylene propylene (FEP) Commonly known by the DuPont™ trademark

Thermoplastic

temperature range.

and are also resistant to burning.

rubber compounds

name Teflon®, fluoropolymers are well suited to

• Melt-processible rubber (MPRI • Thermoplastic vulcanizate (TPVl • Engineering thermoplastic vulcanizate (ETPV!

use in extreme environments: they are inert and

These combine the performance of rubberwith

stable across a wide temperature range.

the processing advantages of thermoplastics.

suitable for food and drink applications, PF is suitable for operating temperatures up to i2o0C (248^). MF forms more cross-links than the other 2, and so has superior mechanical and chemical resistance properties. Applications: Examples include electrical

FORMALDEHYDE CONDENSATION RESINS

Qualities: These are classified as a family

Qualities: These materials contain

Qualities: PF, under the trade name

housing, plugs and sockets, kitchen

together with UF and Formica is a

containing fluorine atoms, which give

elements of rubber but do no"t cross-link

Bakelite, revolutionized the plastics and

equipment, tableware, ashtrays, knife

laminate of paper or cotton and MF.

them superior resistance to virtually all

during shaping, so can be recycled many

design industry. It was invented around

and oven handles, light fittings and

chemicals and an extremely low friction

times.They have similar mechanical and

1900 and became the first commercially

snooker, pool,bowling andcroquet

Costs: PF and UF are low cost. MF is more

coeffi ci ent. Th e low fricti on coeffi ci ent

physical properties to rubber but can be

molded synthetic polymer in the 1920s.

balls. Demand has recently increased

expensive.

acts like a lubricant and stops other

molded on conventional thermoplastic

PF is naturally dark brown or black and so

for under-the-bonnet applications

equipment.This means much more rapid

does not colour easily.

materials sticking to them.

processing times.They typically range from shore hardness 20 to 90A. These materials are resistant to

UF and MF are sub-categorized as

in battery-powered cars because

these materials provide the electrical

amino resins.They are naturally white

insulation and stability that is required

or clear and so are available in a range of

at a reasonable price. They are used in adhesives for

abrasion, chemicals, fuels and oils.They

vivid colours. In the 1930s, they began to

have high impact strength, are flexible

replace PF for use in domestic products

laminating plywood and they are

even at low temperatures and resistance

like tableware.

impregnated into papers andfibres.

toflexural fatigue. MPR can withstand

Formaldehyde resins are resistant

constant use at 1250C (2570F) and ETPV up

to moisture absorption and so do not

toi500C (3020F).

stain easily.They are tasteless and so are

For example, DuPont™ Nomex® (see

polyamides, page 438) is impregnated with PF, laminated wood is bonded

Mebel clam ashtray Designer/client; Alan Fletcher/Mebel Date: 1970 Material: Melamine Manufacture: Compression molded

Vinyl esters

EPOXIES AND COMPOSITES

Lux table

and composites • Vinyl ester

Vinyl esters bridge the gap between polyester and epoxy resins.

Qualities: These materials are similar to polyesters.They are also catalyzed with

methyl ethyl ketone peroxide (MEKP). However, the reaction does not produce as much heat, so thicker sections can be cured. This leads to faster cycle times. They are tougher and more resilient than polyesters, and they are less prone

Polyesters and composites

POLYESTERS

to water absorption and more resistant

Material memories

to chemicals.

Designer; Rob Thompson

Date: 2002 • Polyester

Material: Polyester resin and natural fibres

Polyesters are the least expensive composite

Manufacture: Composite laminating

As with polyesters, styrene is offgassed by the material. Applications: Vinyl esters have become

laminating resins.

popular laminating materials because they are less expensive than epoxy, but have superior properties to polyester.

Qualities: These differ from thermoplastic polyesters (page 437) because they are unsaturated, with double bonds between molecules.

visible texture on the surface. Gel coats are used to minimize print through. They are naturally translucent and can

Styrene is added to assist

Costs: Low to moderate. Applications: A range of composite

more liquid, so it can be cast or laminated

applications such as automotive body

at room temperature. Polymerization

panels, lorry cabs, cherry picker cradles

is catalyzed with methyl ethyl ketone

and boat hulls.They are prone to water

peroxide (MEKP). MEKP is not part of the

absorption, so have to be covered with a

polymerization process; it activates it and

gel coat or vinyl ester for increased lifespan in outdoor and marine settings.

Polyesters exhibit high levels of shrinkage, in the region of 5-10%.This

cars, aeroplane fuselage, wings and interiors.

be coloured to form an opaque material.

polymerization. It makes the material

causes a rapid exothermic reaction.

They are used in mold making, racing

Costs: Low.These are the least expensive

causes fibre reinforcement and other

of the 3 main laminating resins:

fillers to'print through'and create a

polyesters, vinyl esters and epoxies.

EPOXIES AND COMPOSITES Carbon chair Designer/ Bertjan Pot and Marcel Wanders/ made by: Moooi Date: 2004 Material: Carbon fibre reinforced epoxy

Epoxies are suitable for outdoor and marine applications because they are not prone to water absorption. Costs: Moderate.

resin (EP) Manufacture: Carbon fibre saturated in EP is hand-coiled over a mold.

Epoxies and composites • Polyepoxide resin (BP)

little during polymerization, typically

POLYURETHANES Maverick Television awards

less than 0.5%. Epoxies are electrically

Epoxies are high performance resins. They form

insulating and have high resistance

very strong bonds with other materials and so

to chemicals.They are suitable for

are applied as coatings and adhesives as well as

high temperature applications, up to

laminated and molded products.

Polyurethanes • Polyurethane resin (PUR)

Designer/client: Maverick Television/Channel h,

PUR is a versatile material available in a range of densities and hardnesses, used as a solid cast

Date: 2005 Material: Polyurethane resin (PUR)

material, foam, adhesive and liquid coating.

Manufacture: Vacuum casting

200°C (392°F), and also have very good resistance to fatigue. Qualities: Epoxies are naturally clear and

Applications: Epoxies are used in many

Qualities: PUR is naturally tan or clear,

injection molded (page 50) materials

rigid. They can be pigmented and filled with metallic flake. It is also possible to fill them with objects and materials

different formats such as liquid for

and available in an almost unlimited

like PR (see polyolefins, page 430), ABS

casting and laminating, paint, coating

colour range (see image, above right).

and encapsulation, structural adhesives

(see styrenes, page 432) and nylon (see polyamides, page 438). Snap fits, live

during casting. ,

and impregnated in carbon fibre weaves.

Thermoplastic polyurethanes (see page 436) are used in molding and coating

hinges and other details otherwise

Laminated products include furniture,

applications such as trainer soles, sports

limited to injection molding can be

is facilitated by a hardener, which makes

boat hulls, canoes, automotive panels

wear and golf balls. PUR prototyping

made by vacuum casting (page 40) and

up 1 half of the resin,They shrink very

and interiors.

materials are designed to mimic

reaction injection molding (page 64).

Epoxies are not catalyzed.The reaction

SILICONES Flexible ice cube tray Designer/client: Unknown Date: Unknown Material: Silicone Manufacture: Compression molded

POLYURETHANES Open-cell foam balls Made by: Various

Material: Foamed polyurethane resin (PUR] Manufacture: Reaction injection molded Notes: Most plastic can be foamed with open or closed-cell structures.

PUR is used for prototyping and low volume production. Examples include car bumpers, dashboards and interiors, toys, sports equipment and housings for

SILICONES

SILICONES

Animal rubber bands

Skin Light

Designer/client: D-Bros/H Concept

Designer; PD Design Studio Date: 2006

Date: 2003 Material: Silicone

Material: Silicone

Synthetic rubbers »Isoprene rubber [IRl • Chloroprene rubber ICR) • Ethylene propylene rubbers [EPM and EPDM] • Butyl rubber (lIRl • Butadiene rubber IBRl • Acrylonitrile butadiene rubber (ABRl • Styrene butadiene rubber ISBR)

Manufacture: Extruded and cut

Manufacture: Cast

and have low levels of volatile organic

Typical uses include O-rings, gaskets,

There are several different types of

weather strips, seals, medical and

synthetic rubber.They are used in place

surgical equipment, and food processing

of natural rubbers. They have shape

(for example, molds for chocolate).

memory and so will return to their

consumer electronics.

PUR drawn fibre is resistant to cutting and abrasion and is used in textiles, shoe uppers and sports equipment. PUR materials are resilient and

As an adhesive and coating PUR is

durable, and resistant to flexural fatigue,

used to protect and bond wood with

abrasion and tearing.They operate at

other materials. It is quick drying and

compounds (VOCs), which makes them suitable for food preparation and

temperatures up to i2o0C (2480F), but

forms a watertight and rigid seal.

packaging and medical applications.

tbey are affected by ultraviolet light and will become hard and brittle with

Silicones have a wide operating Costs: Low to moderate.

prolonged exposure.

Applications: More than half of all PUR is foamed.There are 3 main types: spray

Silicones

Spray foam is used for filling holes, as insulation or adhesive and to fill cavities in products to make them more rigid.

• Silicone resins

These are low strength but highly versatile materials. They are used as adhesives, gels, rubbers and rigid plastics. They have excellent are chemically inert.

melamine resin

uncertain whether silicone causes tissue

abrasion, have good low temperature

modified with a carbon additive to make

disease and so it is not recommended for

properties, good resistance to chemicals

them conductive.

more than 25 days in the body. As a liquid it is used as a lubricant and

and are typically electrically insulating. IR is the synthetic version of natural

fuel, and SBR is the cheapest and most

release agent in RIM (page 64), composite

rubber (page 447) and consequently has

common form of synthetic rubber.

laminating (page 206) and compression

similar characteristics and applications.

SBR is a widely used low cost rubber

CR was the first synthetic rubber,

with properties similarto natural rubber.

(page 50), compression molding (page 44), casting (page 40) and extrusion. They are used by model m