ME3162 Summary

COLD WORKING

TENSILE DRAWING

WELDING

LASER BEAM WELDING

strength (directional)

For very small diameter

For inaccessible parts cause tiny

surface hardness + wear resistance

To reduce cross section of bars and tubes

Low carbon steels excellent for welding

surface finish & tolerance

Seamless tubes of very high strength

No oxide layer

Stronger than cold rolling

Some too brittle to be coldworked

Best straightness

Subsequent operations difficult

Must be done COLD -

Directional properties

Large parts need ↑energy ↓corrosion resistance ↑electrical resistance

Higher carbon steel and iron need special techniques Non-ferrous need special techniques Quick, convenient Cheap

Defects are common (porosity, inclusions)

Good for m.p. metals

Strongest of all manufacturing processes

For thin sheets

Faster Oxide layer Some metals cannot Expensive ROLLING

Rough surface Slow

metal cracking

ductility

Cheap

Can make complicated shapes

GAS WELDING

Repairs casting defects

No size limit

Dependent on human factors

FORGING

power

SAND CASTING

No directional properties

HOT WORKING

No annealing needed

(Advantages same as Electron Beam except EBW need  vacuum)

Only affect the weld area microstructural properties

Needs annealing to relieve stress

Grain refinement possible

Energy easily controlled

Durable, reliable Very  strength

Cheap, portable No electricity needed

Poor dimensional tolerances DIE CASTING Ideal for  m.p. materials  production rate

 toughness

Metal with high heat conductivity conducts heat away

 surface finish and tolerances

 fatigue strength

ARC WELDING

Can be used for non-ferrous metals

 surface hardness

Thicker sections

 alloying

 wear resistance

Will burn thin sections

One directional

Suitable for mass production

Faster and greater depth of penetration

Parting line (MOST CASTING)

Any metal can use Creates fibrous structure which cannot be removed

Must have  heat conductivity Slow

CENTRIFUGAL CASTING

To  thickness Only ductile metals can be cold rolled Zn & Mg cannot Cold rolling – Shining surface + small thickness Better homogeneity – tough Cheaper than extrusion For thin materials • •

Cold Hot

EXTRUSION For soft material and uniform cross section Create tube with no seam No point of weakness Steel hard to extrude unless want seamless -

Prefer rolling

Can produce hollow sections Good dimensional accuracy (straight) Surface defects when metal leaves chamber •

Direct

Expensive

Flux corrode aluminium

Finer grain size – tougher

•

Hammer Forging

RESISTANCE WELDING

Cleaner

•

Drop Forging

Ideal for steels – high resistance

Dense structure, free of defects

Superior mechanical properties

Impossible for low resistance metals

 production rates

Comparatively high production rate

Both metal must about same thickness

Best mechanical properties for casting

High density

Localized heat

Accurate

•

Fast

CONTINUOUS CASTING

No filler metal

For recycling

Easily automated

Don’t need to cast ingots

High cost

Fully automated

Difficult to join different thickness

Cheap

SUBMERGED ARC WELDING

Quick

Press Forging

Better homogeneity Better dimension Better than hammer forging For finishing, secondary and larger sections More expensive

Automatic feed

•

Upset Forging Done along its length

Molten flux forms protective coating

•

Roll Forging

 welding speed SHEET METAL WORKING Usually mild steel Start with blank or sheet metal to form thin metal products Usually done cold unless sheet too thick RUBBER PAD FORMING

Lots of space and $ Automation necessary FRICTION WELDING

INVESTMENT CASTING Very  surface finish Complicated shapes  tolerances Can use high m.p. metals

Can join dissimilar metals

Good for Tungsten and Cobalt (hard to machine)

Fast

Expensive

Only for ROUND sections

Limited size

METAL INERT GAS WELDING

Slow

•

Indirect

No need die

No need to remove flux

•

Impact

SHEARING

Hot

Trim out smaller sheet

Ideal for sheet metal & positional work

•

Long pieces of uniform cross section •

Cold

•

Hydrostatic

Fast Blanking (save round part) Piercing (throw round part)

Don’t need to replace electrode (TIG)

ALL CASTING SHRINKS – POOR TOLERANCE Casting defects – porosity, cracking (fast cooling)

More flexibility (TIG) More expensive

All casting not very strong

Less likely to crack Very thin tube + brittle materials High reduction in crosssectional area POWDER METALLURGY

PLASTICS

CALENDARING

TIPS

Strength determined by density

Colour choices

Thermoplastics only

Pipe and tube

 m.p. materials can fabricate below m.p.

 Thermal insulation

Similar to rolling

Material

 Electrical insulation

Thinner than Extrusion

•

|Softer, lower m.p. Cheaper

Close to final shape

 Corrosion resistance

Non-metallic constituents can be added

Light

THERMOFORMING

 tolerances

Easy to process

Thermoplastics only

No waste

Cheap

Similar to sheet metal forming

 speed

Rigid, transparent or translucent plastics can be made

 cost

Cannot repair

Die must be simple & one direction

Absorbs odours

Size limited by dies

Not for  temperature

CASTING For prototyping Thermoplastics and thermosets Cheap

•

Aluminium, copper, brass: EXTRUSION 

Steel, stainless steel: COLD ROLLING

|When welding might have air trapped  For low strength application only |Steel is expensive for extrusion

Brittle

Creep under load

PLASTISOL MOLDING

For high strength use,

 tensile strength

Weak mechanical properties

Coating

EXTRUSION or MENNESSMANN

 ductility, fatigue

Deteriorate under Sun

 create seamless tubes

Difficult for low m.p. – melt Cannot be cold-worked or bent INDUCTION WELDING OF COLD ROLLED STRIP Low cost Will have seam Low strength

INJECTION MOLDING

LAMINATING

Thermoplastics only

Coating

Similar to die casting

Plane flat sheets only

Large scale production

REINFORCED MOLDING

Will have parting line

Making composites

Welded by Electrical Resistance welding

Not limited to plane flat sheets FOAM MOLDING

Not good for good conductors

Create sponge-like material

(REFER BOOK. SHORT CHAPTER)

For raw material must always HOT ROLL Normally the raw material comes in big blocks  Hot roll faster in reducing size

Cold rolling always the BEST and CHEAPEST for bar with uniform cross section  quick mass production

Die casting more expensive than sand casting ELECTRICAL DISCHARGE MACHINING Used to make molds Harden before machine

COMPRESSION MOLDING

BRASS

Thermoset only

Corrosion resistant

Similar to press forging

Strong

Large scale but slower than Injection

Durable

All automated Can machine hard material  tolerance No mechanical strains

Gold TRANSFER MOLDING

Expensive

Same as Compression No flash

STAINLESS STEEL

Forging even more expensive

If diameter >10mm, cannot extrude directly

Workpiece must be electrically conductive Very slow Electrode wear – poor tolerance

Can mold small intricate parts

Silver Durable

REACTION INJECTION MOLDING

Corrosion free

Hybrid of Compression and Injection

Expensive

WIRE CUT EDM High precision machining Complicated profiles

MILD STEEL EXTRUSION Thermoplastics only Very large scale

Cheap Strong Corrodes

No need high temperature BLOW MOLDING MEDIUM CARBON STEEL Thermoplastic only Strong Large scale Expensive ROTATIONAL MOLDING Thermoplastics only Cheap Slow Small scale

ALUMINIUM Corrosion resistant Strong Not as shiny

THERMOPLASTICS

Polypropylene

Epoxy

Acetal (Polyacetyl)

Stronger

High strength

Very  strength but not boiling water

Can stand boiling water

Very chemically inert

Used for load-bearing components

Soft

Very corrosion resistant

Floats in water

Dimensionally very stable

More expensive

Excellent adhesive

Acrylic Most transparent Became opaque from UV

Tends to be brittle Refer book for LDPE (extremely cheap), HDPE, UHMWPE and PP

Cellulosics Extremely cheap Comes in many forms Transparent unless altered

Expensive

Phenolic Polyurethane Replacement for rubber

Excellent chemical, electrical and heat resistance Extremely hard and brittle

Used in non-foam (solid) form Polyesters

Fluorocarbons Can stand  temperature and corrosive environments

Styrenes Cheap

 weathering characteristics Corrosion resistance

Transparent

 coefficient of friction

 for low and sub-zero temperature

 surface energy (non-stick)

Non-toxic

Expensive

Will get dented

Heaviest of all common plastics

Brittle

Polyamides

ABS

Polyurethane Flexible Last much longer than Styrofoam More expensive

Silicone

Nylon

Opaque

Soft and rubbery

Excellent toughness & wear resistance

Impact resistant

 coefficient of friction

Cannot stand boiling water

Often used to replaced rubber when  temperature is encountered Convenient for making large objects and for joining/sealing purposes

Cheap Used for load bearing if dimensions not critical

SAN

Poor dimensional stability

Transparent Can stand boiling water

Aramids

More brittle

Very  strength and stiffness Bulletproof

Vinyls (PVC) Cheapest

Polyesters

Transparent

Polycarbonate

Rigid and hard

 impact stress

Cannot stand boiling water

Can stand boiling water Transparent

PET

THERMOSETTING RESINS Generally can be used at higher temperatures but brittle

High boiling point but changes shape Amino Plastics (Formaldehyde) Polyolefins Corrosion resistant Non-toxic Waxy surface

Hard surface Wear resistant Strong Stain resistant

Caseins Polyethylene

High flexural strength

Very light

Tough

Can stand very corrosive materials

Obsolete and seldom used

Cannot stand boiling water

MACHINING AND MACHINE TOOLS

For small ae / dt

Shear plane model

Cutting Rotational motion of the workpiece at V relative to the tool

Material removal rate ae-depth of cut| ap-width of

workpiece

Machining time

tm=lw+dtVfif face milling

Drilling Chip cross-section area Ac

Undeformed chip thickness

Ac=fap

The apparent shear strength of the material τs on the shear plane

where f is the feed per revolution

f =Vfnw Material removal rate

kr is the major cutting edge angle

Machining time

Zw=AcVav=fapVav =πfapnw(dm+ap) lw is the length of the drilled hole nt is the rotational frequency of the tool

Power required Material removal rate

Pm= psZw ps – specific cutting energy Electrical power consumed

Pe=Pmηm Vertical milling

Maximum undeformed chip thickness

=af=fN=VfNntif face milling

TOOL WEAR AND TOOL LIFE

MECHANICS OF METAL CUTTING Specific cutting energy

Specific cutting energy ps :

Economics of metal cutting operation Average cost per workpiece

Depreciation time

Average cost per workpiece

Where Tool cost a) Regrindable tools

(b) Disposable inserts

Number of tools required

Minimum Cost Cutting speed

Tool changing time

t = tool life

Machining time

Tool life Machine Tool Maximum Power Restriction

c, α and β are constants

Minimum Production Time where

Cutting speed

Maximum Force Restriction

Tooling cost and tool changing cost per workpiece

Tool life

Surface Finish

R is tool nose radius

Number of tools per workpiece

Estimation of cost Factors Total Machine and Operator Rates

Total production time = no. of pieces x (loading time + tool return time + rough cut time + finish cut time) tmr=Volume of removed materialZw