Tool Design Theory (DCD)

TRAINER GUIDE - II TOOL DESIGN THEORY (DCD) (5TH SEMESTER)

DTM

MSME TOOL ROOM INDO GERMAN TOOL ROOM AHMEDABAD

SUBJECTS & COURSE CONTENT In

DIPLOMA IN TOOL & DIE MAKING (DTM)

VERSION - 0

NAME OF THE SUBJECT THEORY /PRATICE HRS.PLANNED TOOL DESIGN THEORY - DIE CASTING DIES 160 SUBJECT OBJECTIVE : This subject under Core Technology Group intended to teach the trainess and make them to understand & apply the concept, principle and procedure of knowledge in design of Die Casting Dies and other metal casting process for different types of ferrous and non ferrous alloys.

UNIT A Introduction

B Die casting operations

CHAPTER NO. CHAPTER A1 Over view of mass production of Casting Parts Produced by various Casting Process

B1

B2

Gravity die casting

PART

THEORY TOPICS & SUB TOPICS A.1.1.1 A.1.1.1(a) A.1.1.3(a) A.1.1.3 A.1.1.3(a) A.1.1.3(b) A.1.1.4 B.1.1.1 B.1.1.2 B.1.1.3 B.1.1.4 B.1.1.4(a) B.1.1.4(b) B.1.1.4(c) B.1.1.5 B.1.1.6 B.1.1.7 B.1.1.8 B.1.1.9 B.1.1.10

Pressure Die casting (cold chamber) B.2.1.1 B.2.1.2 B.2.1.3 B.2.1.4 B.2.1.5

Die Casting Background What is Die Casting Ciassification Of Castings Principle Of Die Design And Process Advantages Of Die Casting Techniques Technique of filling die cavity Comparision of die casting with other products. Introduction Gravity die casting process Limitation of permanent mould castings Principle Of permanent mould casting Progressive solidification Minimum turbulance Air and gas clearance Suitable casting metals for GDC Selection of mould materials Permanent mould casting machines Gravity die casting mould Principle of mould design Solid graphite permanent mould Introduction Pressure die casting machines Classification of die casting machines Cold chamber machines Cold chamber machines and parts

B.2.1.6 B.2.1.7 B.2.1.8 B.2.1.9

Classification of cold chamber die casting machines Horizontal cold chamber die casting machine Vertical cold chamber die casting machine Comparision of cold and hot chamber process

B.2.1.10

Process parameters and controls Cold chamber die casting processing metals alloys

B.2.1.11

and

PRACTICE TOPICS & SUB TOPICS

SUB CODE

B3

Pressure Die casting (hot chamber)

B.2.1.12

Cold chamber die casting die

B.3.1.1 B.3.1.2 B.3.1.3 B.3.1.4

Introduction Classification of die casting machines Hot chamber machines Hot chamber machines and parts

B.3.1.5

C2

Classification hot chamber machines Introduction toof various defectsdie of casting die casting Defects and remedies of die B.4.1.1 casting components components B.4.1.2 Identification of defects B.4.1.3 Classification of defects Description for different types of defects and their B.4.1.4 causes and remedies Introduction of feeding system of die casting Feeding system C.1.1.1 components C.1.1.2 Definition of elements and fuction of feed system C.1.1.3 Feed system for gravity die casting dies C.1.1.4 Feed system for hot chamber castings dies C.1.1.5 Feed system for core chamber casting dies C.1.1.6 Classification of gate systems C.1.1.7 Principle of feed system C.1.1.8 Balancing of feed system Cooling system C.2.1.1 Introduction to cooling of die casting dies

C3

C.2.1.2 C.2.1.3 C.2.1.4 Ejection system or techniques C.3.1.1

B4

Elements of die casting and their C function

D Material handling

C1

D1

Pre-casting

D2

Post-casting

C.3.1.2 C.3.1.3 C.3.1.4 D.1.1.1 D.1.1.2 D.1.1.3 D.1.1.4 D.1.1.5 D.2.1.1 D.2.1.2 D.2.1.3 D.2.1.4 D.2.1.5 D.2.1.6

Definition of elements and fuction of cooling system Principle of cooling of die casting dies Classification of cooling systems Introduction Various elements of ejection techniques and fuctions Various ejection techniques Principle of ejection system Introduction Principle of metal casting technique Classification of metal casting technique Pre-casting techinque Pre-casting techinque related equipments Introduction of post-casting technique Principle of metal casting technique Classification of post-casting techniques Trimming Post machining Surface decoration

D.2.1.7 D.2.1.8 D.2.1.9

E Maintenance, safety and storage

E1

Coating Deburing operations Post-casting related equipments Indroduction to understand the necessity of maintenance, safety and storage of die casting dies Maintenance, safety and storage E.1.1.1 with respect andtomachines die casting die and machine E.1.1.2 Concept of safety E.1.1.3 Concept of maintenance E.1.1.4 Concept of storage E.1.1.5 Safety of die casting die E.1.1.6 E.1.1.7 E.1.1.8 E.1.1.9

F Specification

F1

G Computer aided information analysis

G1

D

D2

D D D D D D

Safety of die casting machines and their equipments Safety of personnel Check list for maintenance of die and machines Storage of die casting die Introduction to use and application of the specifications pertaining to die casting dies, materials and machines Specification of die, material F.1.1.1 and machines for tool design data F.1.1.2 Die casting die specification F.1.1.3 Die casting metal specification F.1.1.4 Machine specification F.1.1.5 Specification for processing Introduction to use and application of simulation Introduction of simulation andG.1.1.1 analysis packages package G.1.1.2 Concept of process parameters G.1.1.3 Classification of simulation packages Principle of selection of process parameters using G.1.1.4 software packages

TD 1.2,5.3d Preparation & Work /Data Sheet & Mold, Material &Machine

TD 2.1 TD2.2 TD2.a TD2.2b TD2.2c TD 2.2d

Introduction to Use & Work sheet for Mold Design Definition , Concept & Principle & Mould ,plastic material Specification Estiimation & material Machine hours process parameters

D D

TD 2.2e TD 2.2f

D D D D D E Conceptual Design E E E E E

TD 2.2g TD 2.3 TD 2.4 TD 2.5 TD 2.6 TD 1.1 TD 1.1a TD 1.2 TD 1.2a TD 1.2b TD 1.3

E E F Design & Moulds F F F F G Mould Data G G G G G G H CAD/CAE H H H H H H

E1 Sketching Conceptual

TD1.3a TD1.3c

F1 Draw the assembly and Details diagrams & mold

G1 Bill & Materials

G2 Mould Data H1

H2 Introduction to Design & mould wih CAD

TF1.1a TF1.1b TF1.1c TF1.1e TF1.1f TG1.1(a) TG1.1(b)

Component Geometry dimensional and tolerance & Constraint Mold design work/data sheat format for the design parameter with respect to Mold , machine material & process parameters Work sheet for ijection mold Work/Data sheet for mold Compression Work/ Data sheet for parameters Work/Data sheet for Blow mold Introduction Application & atternative Conceptual Design Definition & Concept & Conceptual Design Evaluation Procedure Develop alternative Conceptual design Using design Parameters Select the optimal Design

TH 1.1 ( d)

Flow Chart for Development & Design Preparation Design Data Sheet Preparation Concept Drawing Assembly Drawing method (TA 1.1.c) Details Drawing method Introduction to Bill & Material Elements & Bill & Material Preparation & Bill & Material by Appropriation Selection & Material, Material size Representation & Standard parts in Bill & Material Introduction to mould Data different Element & mold Data Preparation & mold data Introduction to CAD/CAE SoftWare mould Design Soft wares Application & Softwares in plentic Processing Different Types & Application SoftWarer for the plastic processing

TH .2 .1 (a)

Different types & soft wares for mould Design

TG1.1 ( c ) TG.1.1 (d) TG. 2.1 (a) TG.2 .1 (b) TG.2.1 ( c) TH 1.1 (a) TH 1.1(b) TH 1.1 ( c )

TH 2 . 2 (b) Difference between 2D Drawing to 3D Solid models TH 2.3 ( c ) Sequence & mould Design Using CAD Package

H H H

TH 2.4 ( d ) TH 2.5 ( e) TH 2.6 ( f)

Details Drawing from Assembly Drawing Associativity between 3 D model to 2D Drawing Advantage & 3D model CAD Soft wares

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DIE CASTING TG-2 THEORY

UNIT-1 CHAPTER – A1 OVERVIEW OF MASS PRODUCTION OF CASTING ARTS PRODUCED BY VARIOUS CASTING PROCESS

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CHAPTER OUTLINE A1.1.1

Die casting Background

A1.1.1 (a)

what is Die Casting

A1.1.2

Classification of Castings

A1.1.3

Principle of Die Design and Process

A1.1.3 (a)

Advantages of Die Casting Techniques

A1.1.3 (b)

Technique of filling Die Cavity

A1.1.4

Comparison of Die Casting with other Process

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A1.1.1

DIE CASTING BACKGROUND

Die casting are among the highest volume, mass - produced items manufactured by the metalworking industry. Die casting are important components in thousands of consumer, commercial and industrial products such as automobiles, household appliances, recreation, hobby and leisure -time products, farm and garden equipment, elec trical equipment and ordnance, general hardware, power tools, computers and other business equipment, instruments, toys, novelties and a great many other too numerous to mention. In fact, die casting have greater utility and are used in more appl ications than components produced by almost any other metal forming process. Die –casting is a process involving the injection of molten metal at high pressure (as opposed to casting by gravity pressure). It is beloved to have begun sometime durin g the middle of the 19 th century. According to records, in 1849, Sturges patented the first manually operated machine for casting printing type. Another 20 years passed before the process was extended to casting other shapes. The casting of printer’ s type led to patents which eventually resulted in development of the Linotype machine by Ottoman Megenthaler. The earliest commercial applications for die castings occurred in 1892 when parts were produced for phonographs and cash registers. Mass product ion was further encouraged when the H.H. Franklin Company began die casting Babbitt alloy bearings for automobile connecting rods shortly after the turn of the century. Various compositions of tin and lead were the first die casting alloys. Their importance and use declined, however, with the development of zinc alloys just prior to World War I. Aluminum alloys for die casting made their commercial debut about 1914. Magnesium and copper followed shortly thereafter. During the 1930s, many of the alloys we know today had become available. Modern science and technology, metallurgical controls and research are making possible still further refinements resulting in new alloys with increased strength and stability. Through the years, many significant technol ogical improvements have been made to the basic die casting process, to die steels and to die construction, as well as in casting machine design. Improvements have not only extended the capability and production capacity of the process, they have been tremendously effective in expanding die casting applications into almost every know market.

A1.1.1 (a) WHAT IS DIE CASTING Die casting is a manufacturing process for producing accurately dimensioned, sharply defined, smooth or textured -surface metal parts. It is -3-

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accomplished by forcing molten metal under high pressure into reusable metal dies. The process is often described as the shortest distance between raw material and finished product. The term, “die casting” is also used to describe the finishe d part. The term “gravity die casting” refers to castings made in metal molds under gravity head. It is known as permanent mold casting in the U.S.A and Canada. What we call “die casting” here is know as “pressure die casting” in Europe. Ever since m an discovered that metals could be melted, he had tried to form these metals into shapes useful to him by pouring the liquid metals whose shape they retain during and after solidification. The casting of molten in moulds is one of the oldest methods developed by man to shape metal objects. These are called molding or casting and are classified depending upon the molding method, mould material or casting process employed.

A1.1.2

CLASSIFICATION OF CASTING

1. Sand Castings: a. Green sand molding b. Dry sand molding c. Shell molding d. High pressure molding (using high pressure molding machine) e. Floor and pit molding 2. Metal mould castings: a. Permanent mould (gravity die casting) b. Semi- permanent mould casting (using metallic molding machine) 3. Plaster mould casting. 4. Investment casting. In metal mould castings, the mould consists of two or more parts, is used repeatedly for the production of many casting of t he same form. Where as in the other molding processes the mould is destroyed for each casting produced. A great deal of these type of casting processes are still employed for the production of castings. The summary of each of these molding and cas ting processes is furnished for comparative study at the end of this chapter. Each method has its own advantages and disadvantage like finish, dimensional accuracy etc. In order to produce cast articles more efficiently the permanent steel mould was developed. The molding of non - ferrous metals and their alloys with relatively low melting temperatures in permanent steel mould under pressure is called Die Casting. Castings produced by pressure die casting process are distinguished by their characterist ic accuracy smoothness and surface quality The die castings are made with minimum expenditure of metal and they are accurate in sized to -4-

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the extent that very little or no subsequent machining is necessary after removal of the gate and flash . Th e die castings made with hot or cold chamber machines are called Pressure Die Casting.

A1.1.3

PRINCIPLE OF DIE DESIGN AND PROCESS

First, a steel mold capable of producing tens of thousands of castings in rapid succession must be made at least two secti ons to permit removal of castings. These sections are mounted securely in a machine and are arranged so that one is stationary ( fixed die half) while the other is moveable ( injector die half ) To begin the casting cycle, the two die halves are clamp ed tightly together by the die casting machine. Molten metal is injected into the die cavity where it solidifies quickly. The die halves are drawn apart and the casting is ejected. Die casting dies can be simple or complex , having moveable slides, co res, or other sections depending on the complexity of the casting. The complete cycle of the die casting process is by far the fastest known for producing precise non -ferrous metal parts. This is in marked contrast to sand casting which requires a new sand mold for each casting . while the permanent mold process uses iron or steel molds instead of sand it is considerably slower, and not as precise as die casting.

A1.1. 3 (a) ADVANTAGES OF DIE CASTING TECHNIQUES Gravity Die Casting:The die is built up of parts or elements made of metal ( generally cast iron or steel ) . The design is adopted to the shape of the article required to be produced, so as to enable easy assembly, pouring and extraction These operations constitute a cycle of operations which when repeated in a certain rhythm, determine the output rate of the equipment The various operations of assembly and disassembly of the die may to some extent be mechanized. In this process liquid flows into the die entirely under its own weight. It is form this features that the term “gravity Die Casting” was coined.

Pressure Die Casting:This technique is a development over the gravity die casting and has the following characteristics. a. The die is mounted between the two plates called “PLATENS’ of press, generally of horizontal type, by means of which it is closed and opened.

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b. The movement of the die follows that of the machine, and this determines the general directions of assembly. c. The liquid metal is generally injected by the action of a piston, which forces it through the die from a compression chamber This is referred to as a hot chamber, if it is situated inside the molten metal which is heated by a furnace forming part of the assembly a cold chamber if it is fed with metal which has been melted in a furnace separate from the machine.

Advantages of Pressure Die Casting Process: Die casting components parts, decorative trim, and /or finished prod offer many features, advantages and benefits to those who specify this manufacturing process.

ucts

1. Die casting provides complex shapes within closer tolerance than many other mass production processes. 2. Die castings are produced a t high rates of production. Little or no machining is required. 3. Die castings can be produced with thinner walls than those obtainable by other casting methods …. much stronger than plastic injection moldings with the same dimensions 4. Die casting provide parts which are durable, dimensionally stable, and have the feel and appearance of quality. 5. Die casting dies can produce thousand of identical castings within specified tolerances before additional tooling may be required. 6. Zinc castings can be easily plated or finished with a minimum of surface preparation. 7. Die castings can be produced with surfaces simulating a wide variety of textures. 8. Die cast, surfaces, as cast, are smoother than most other forms of casting. 9. Holes in die castings can be cored, and made to tap drill sizes. 10. External threads on parts can be readily die cast. 11. Die castings provide integral fastening elements, such as bosses and studs, which can result in assembly economics. 12. Inserts of other metals and some non-metals can be die cast in place. 13. Corrosion resistance of die casting alloys rates from goods to high. 14. Die castings are monolithic. They combine many functions in one, complex shaped part. Because die castings do not consist of separ ate parts, welded or fastened together the strength is that of the material, not that of threads or welds, etc. 15. More complex shapes can be produced by the pressure die casting process than gravity die casting, Ex Carburetor. -6-

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16. Since the dies are fil led by pressure, castings with thinner walls, greater length to thickness ratio and greater dimensional accuracy can be produced. 17. Production rates are higher in pressure die casting, especially when multiple cavity dies are used. 18. The castings are p roduced as almost completely finished parts, the investment in inventory and factory floor space reduced to a minimum. 19. Dies for pressure die casting can produce many thousands of castings without significant change in casting dimensions. 20. Metal cost is often lower than in other casting process, because pressure die casting permits components of thinner sections. 21. Many die casting can be plated (finished) with minimum surface preparation. 22. Some Aluminum alloy pressure die castings can be develop ing higher strength than compared sand castings.

The Principle Limitations of the Pressure Die Casting Process: 1. Casting size is limited. The casting weight seldom exceeds 50 1b and normally is less than 15 lbs. 2. Depending on the casting contours and gating, difficulty may be encountered with air trapped in the in the die. Trapped air is principle cause of porosity. 3. The die casting facilities, consisting of the machine, the auxiliary equipment and the dies are r elatively expensive. Because the die castings are small, large quantities of castings are required for the process to be economical. 4. Commercial use of the process is limited to metals having melting temperatures not higher than these of copper - base all oys, with few exceptions. Dies can be produced for simple and complex parts. Parts having external undercuts or projections on side walls often require slides which increase costs. In many cases however, resultant savings of metal or other advantages such as uniform wall sections, offset the extra cost or effect a net economy in overall costs. This is especially true when large quantities are involved.

A1.1.3 (b) TECHNIQUE OF FILLING DIE CAVITY As the name “ Pressure Die Casting” implies, injecti on of the molten metal into the mould or die cavity is done under pressure. The thin walls as well as the various bends around the corners and the edges of complicated die castings offer considerable resistance to complete filling of the mould or die. Therefore it is necessary that the metal moves through the die with high velocity before it settles in the mould cavity. The air present in the cavity has to be displaced by the entering metal. The air could be displaced by providing air vents in the die or by connecting the cavity to vacuum before the metal is injected into the die. -7-

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Vacuum die castings are used only for small parts made of low or high melting light alloys. Pressure die casting necessitates a particularly care fu lly study of the design and shape of the articles to be produced. The choice of technique involved for the production of a given article is governed by many factors, the most important of which are as follows : 1. 2. 3. 4. 5. 6. 7.

Mechanical properties Dimensional accuracy Complexity of shape Surface condition Number of casting to be produced Production time Production cost

Certain considerations of strength, precision or surface condition indicate a particular technique. It is always important that the production cost of the article desired should be estimated. The production cost must take into account. a. b. c. d.

Cost of mould Cost of the injection machine Cost of subsidiary operations (melting. trimming and machining) Actual weight of the metal.

The careful study of the production cost of an article based on the above factors and related to the number of articles to b e produced determines the limit of viability of a particular technique to make the process economical. The advent of mass production has made possible the study and practical application of mechanized means of pressure die casting. As a result of considerable capital investment it is possible to mass produce articles at extremely competitive prices. For example, an electric coffee mill may be sold at a price lower than that of most of its component parts, if these were to be produced individually other than the die casting process.

A1.1.4 COMPARISONS OF DIE CASTING WITH OTHER PRODUCTS Plastics Injection Molding: Compared with plastic injection moldings, die castings are stronger , stiffer, more stable dimensionally, more heat resistant, and ar e far superior to plastics on a properties /cost basis They help prevent radio frequency and electromagnetic emissions. For chrome plating, die casting are much superior to plastic, are completely resistant to ultra -violet rays, weatheri ng , and stress -8-

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cracking in the presence of various regents. Manufacturing cycles for producing die castings are much faster than for plastic injection moldings, Plastics, however, may be cheaper on a unit volume basis, have color inherent pro perties which tend to eliminate finishing , are temperature sensitive, and are good electrical insulators.

Sand Castings:Compared with sand castings die casting require much less machining; can be made with thinner walls; can have all or nearly all holes cored to size; can be held within much closer dimensional limits; are produced more rapidly in dies which make thousands of die castings without replacement; do not require new cores for each casting; are easily provided with inserts die cast in place; have smother surfaces and involve much less labor cost per casting Sand castings, on the other hand, can be made from ferrous metals and from many non -ferrous alloys not suitable for die casting. Shapes not producible by die castin g are available in sand castings; maximum size can be greater; tooling cost is often less and small quantities can be produced more economically.

Permanent Mold Castings:Compared with permanent mold castings, die cast ings can be made to closer dimensional limits and with thinner sections; holes can be cored; are produced at higher rates with less manual labor; have smoother surface and usually cost less per die casting. Permanent mold casting involves somewhat lower tooling costs; can be made with sand cores yielding shapes not available in die casting.

Forgings:Compared with forgings die castings can be made more complex in shape and have shapes not forgeable; can have thinner sections; be held to close r dimensions and have coring not feasible in forgings. Forgings, however, are denser and stronger than die castings; have properties of wrought alloys; can be produced in ferrous and other metals and in sizes not suitable for die castings.

Stampings:Compared with stampings, one die casting can often replace several parts. Die casting frequently require fewer assembly operations; can be held within closer dimensional limits; can have almost any desired variation in section thickness; involve less waste in scrap; are producible in more complex shapes and can be made in shapes not producible in stamped forms. Stampings, on the -9-

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other hand, have properties of wrought metals; can be made in steel and in alloys not suitable for die casti ng; in their simpler forms, are produced more rapidly; and may weigh less than die castings.

Screw Machine Products:Compared with screw machine products, die castings are often produced more rapidly; involve much less waste in scrap; can be ma de in shapes difficult or impossible to produce from bar or tubular stock; and may require fewer operations. On the other hand, screw machine products can be made from and alloys which cannot be die cast; they have the properties of wrought metals; and they require less tooling expense. There are some comparison tables for Die Casting Process with other process with respect to Process, Die/Mold, Cost, Design and application etc., continued in the next page.

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CHAPTER: A1 OVERVIEW OF MASS PRODUCTION OF CASTING ARTS PRODUCED BY VARIOUS CASTING PROCESS

DIE CASTING THEORY

Table : Process

TG-2

SUMMARY OF MOULDING AND CASTING PROCESSES *Choice of materials

Complexity of part

Number of castings

Casting size or weight

relative to tool life Sand

Shell Mould

1, 2 ,3, 4, 5, 6, 7, 8, 9, 10,

Considerable limited by pattern

Wide range, type of pattern

28 gms. To

11,

drawing. No limit with cores.

depends upon total/casting.

1, 2, 3, 4, 5, 6, 9

Considerable, limited by

High metal patterns have a

28 grms – 45 gms and 387

removal of mold from pattern.

long life.

cm2

Limited, restricted by the rigid

Moderate to high , casting

Several grams - 23 kgs.

molds. Ability to eject casting

metal affects life of mold.

Less limited with cores. Permanent Mould

1, 3, 4, 5, 6, 7, 8, 10, 11

limits shape Die Casting

4, 5, 7, 8, 10, 11

Moderate, limited by design of

High, mold life affe cted by

Several grams – 33 kgs. In

movable cores

casting metal.

aluminium 90 kgs. In zinc usually under 7 kgs.

Plaster moulding

4, 5

Considerable, possible to make

Moderate, depends on

28 grms to several kgs. In

mold of several pieces,

pattern material

most of material.

Considerable, very complex

Moderate, type of pattern

Under 28 gms to 45 kgs.

patterns can be assembled

mold depends upon

Best for parts under 0.8 kg.

from pieces.

number of castings.

Casting of circular periphery

Low to moderate

expendable mold Investment Casting

Centrifugal Casting

3, 4, 5, 6, 9

1, 3, 4, 5, 6, 9

most favorable. Almost any shape can be cast. -9-

Upto several kgs.

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CHAPTER: A1 OVERVIEW OF MASS PRODUCTION OF CASTING ARTS PRODUCED BY VARIOUS CASTING PROCESS

DIE CASTING THEORY

TG-2

Process

Min. section mm

Min. dia cored hole mm

Surface finish Microns

Precision and tolerances

Sand

3 – 6 depending upon

4, 5 – 6

6 , 25 - 25

1, 5 – 4, 2 mm depending

metal

upon metal & casting size. Tolerance of ± 0.25 mm possible on some parts.

Shell Mould

1, 5 for most materials.

3–6

Some what better than

± 0, 003 mm/mm 0,075

sand

total possible on some dimensions.

Permanent Mould

2.38 most materials

4, 5 – 6

2, 5 – 6, 25

± 0,015 mm/mm for firs

t

25 mm 0.025 mm to 0.05 mm for each additional 25 mm Die Casting

0.625

0.76 – 4.5 depending upon

1 – 2, 5

metal Plaster moulding

0, 750

±0,025

–

0,125 mm

depending upon material.

12.5

0,75 – 1.25

±0.005 – 0.010 mm/mm or less

Investment Casting

0.750

0.50 – 0.750

0.25 – 2.12

±0.005 mm/mm

Centrifugal Casting

0.750

4.3 - 6

2.25 – 6.25 or as in sand

Same as permanent mould.

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CHAPTER: A1 OVERVIEW OF MASS PRODUCTION OF CASTING ARTS PRODUCED BY VARIOUS CASTING PROCESS

DIE CASTING THEORY

TG-2

Process

Tool costs

Direct Labour costs

Finishing costs

Field of application

Sand

Low

Wide range, much hand labour

Wide range, high to low,

Singular and batch production of

required.

depends upon cleaning,

medium & large components of cast

snagging and machining

iron, cast steel, not precision.

required. Shell Mould

Low to moderate

Moderate

Low, often only a minimum

Batch & mass production of cast iron,

required.

steel components. To reduce the cost of machining.

Permanent Mould

Medium

Moderate

Low to Moderate

Batch Production.

Die Casting

High

Low to medium

Low, little more than

Mass production of small components

trimming necessary.

of Auminium, zinc, magnesium, copper alloys. To reduce the cost of machining.

Plaster moulding Investment Casting

Medium High

High, skilled operators

Low, little machining

Batch Production.

necessary

necessary.

High, many hand operators

Low, machining usually not

Steel, alloyed steel, small batch, small

required

necessary.

size to reduce the expensive machining.

Centrifugal Casting

Medium

Moderate

Low to moderate

Singular batch production bearing sleeves of bearing alloys cast iron tubes.

(1) Gray Iron, (2) Malleable Iron, (3) Steel, (4) Aluminium alloys, (5) Copper alloys (6) Nickel alloys, (7) Zinc alloys, (8) Magnesium alloys, (9) Heat and corrosion resistant alloys, (10) Tin alloys, (11) Lead alloys. - 11 -

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CHAPTER: A1 OVERVIEW OF MASS PRODUCTION OF CASTING ARTS PRODUCED BY VARIOUS CASTING PROCESS

DIE CASTING THEORY

TG-2

DIE CASTING COMPARISON WITH OTHER PRODUCTION PROCESSES Process

Process defined

Materials

Rate of

Size & weight of

Strength

Wall

Complex

Other

production

parts

of parts

thickness

ity

characteristics

Die

Castings made by

Lead, tin,

Very high,

No real size

High unit

Very thin; upto 1

From

Inserts of almo st

casting

forcing molten metal

zinc

upto 500

limitation. Size

strength.

in or more max.

simple to

any metal can be

under external pressure

magnesium

shots/hr

depends upon

very

embedded in

into a metal die or

, aluminium

possible with

casting equipment

complex.

castings.

mold.

and copper

some parts.

available. Present

Not so thin as

Usually

Inserts can be used.

alloys.

max. sizes run : 15 lb for aluminum, 10 lb for magnesium and 30 lb for zinc.

Permanen

Castings produced by

Iron,

Relatively

Usually medium or

High

t mold

pouring molten metal

manesium,

low. Not a

large parts. Between

die casting but

not so

casting

under a gravity head

aluminum

high

die, castings and

much heavier

complex

into metallic molds.

& copper

production

sand castings.

sections

as die

alloys.

process.

possible.

castings.

Sand

Castings made by

Principally

Low. Not a

Medium to very

Less than

Must be heavier

Housings

Inserts seldom

Casting

pouring molten metal

iron,

high

large.

die castings

than die

& hubs

practical.

under a gravity head

magnesium

production

or

castings &

represent

into molds prepared by

, aluminum

process.

permanent

permanent mold

average

packing molding sand

& copper

mold

castings can be

degree of

around a suitable

alloys.

castings.

cast in sections

complexity

1 ft or more.

.

pattern. - 12 -

INDO-GERMAN TOOL ROOM, AHMEDABAD

- 13 -6 DIE CASTING THEORY

CHAPTER: A1 OVERVIEW OF MASS PRODUCTION OF CASTING ARTS PRODUCED BY VARIOUS CASTING PROCESS

Plaster mold

Castings made by

Any nonferrous

Low. Not a

casting

pouring metal under

material having

a gravity head into

Relatively small.

TG-2

Equal to

Not as thin as

Usually not

high

sand

lead, tin or zinc die

so complex

a melting point

production

castings.

castings, but

as die

molds made of

of less than

process.

sometimes equal

castings or

gypsum with

2000 F, except

to die castings of

permanent

strengthening &

magnesium in

aluminum,

mold

setting agents

large sizes.

magnesium &

castings.

added.

brass.

Precision

Castings made by

Iron, zinc,

Usually

Small parts only.

Equal to or

0.040 in. min. 1/16

Intricate

Min. thickness

investment

pouring molten

magnesium,

lowest of

Max weight of part

better than

in. prescribed min.

shapes not

of trailing edge

casting

metal into refractory

copper alloys &

all

about 101b or up

permanent

tolerance on walls

readily

equal to 0.015

or ceramic molds

especially hi gh

processes

to 201b by special

mold

no less than 0.005

made by

in. min. &

formed around wax

alloy steels.

techniques.

castings.

in. min.

machining,

preferably

patterns. Patterns

Section size

forging or

0.025 in.

are removed by

usually limited to 7

sand casting

inserts not

melting in the

in. or less.

can be

practical.

process of firing of

produced.

the refractory.

- 13 -

INDO-GERMAN TOOL ROOM, AHMEDABAD

- 14 -6

CHAPTER: A1 OVERVIEW OF MASS PRODUCTION OF CASTING ARTS PRODUCED BY VARIOUS CASTING PROCESS

DIE CASTING THEORY

TG-2

COMPARISON OF DIE CASTING WITH OTHER PRODUCTION PROCESS (Contd…) Process Die casting

Appearance & finish

Cost

Applications

Excellent. Can be finished with variety

High equipment cost, high tool cost, &

Structural parts, machine elements &

of mechanical, plated, chemical or

low labor cost. Low part cost on high

decorative members & parts for automotive,

organic finishes.

activity items. Machining, grinding &

business, machine electrical appliance, & all

other operations usually not

other high production industries making both

necessary.

industrial & consumer products.

Permanent mold

Usually machined or ground but left with Medium equipment cost, high tool

For parts similar to sand castings but which

casting

base metal surface.

cost, high labor cost. Fairly high part

must have superior surface finish, closer

cost.

tolerances, & better strength in as cast condition.

Sand casting

Inferior to die or permanent mold

Low tool cost, high equipment cost,

Gears, framing members, housings motor

castings. Usually machined or ground

high labor cost part cost between

blocks & structural members when cast

but left with base metal surface.

those of die castings & precision

structure having relatively low strength &

castings.

resistance to impact satisfactory. Usually limited to cast iron & cast steel for industrial equipment.

Plaster mold

Excellent

casting

Low tool cost, low equipment cost,

Various engineering parts, mostly of brass

high labor cost, fairly high part cost.

alloys.

Precision

Equal to die castings, but usually left

Low equipment cost, low tooling cost,

Small intricate parts made in limited

investment casting

with base metal surface.

high labor cost, high part cost.

quantities, usually from high alloy metals such as stainless steel. Inconel Hastelloy etc.

- 14 -

INDO-GERMAN TOOL ROOM, AHMEDABAD -16 DIE CASTING THEORY

CHAPTER: B1 GRAVITY DIE CASTING

UNIT-2 CHAPTER – B1 GRAVITY DIE CASTING

-1

TG-2

INDO-GERMAN TOOL ROOM, AHMEDABAD -216 DIE CASTING THEORY

CHAPTER: B1 GRAVITY DIE CASTING

CHAPTER OUTLINE B1.1.1

Introduction

B1.1.2

Gravity Die Casting (GDC)

B1.1.3

Limitations of Permanent Mold Casting

B1.1.4

Principle of Permanent Mold Casting

B1.1.4 (a)

Progressive Solidification

B1.1.4 (b)

Minimum Turbulence

B1.1.4 (c)

Air and Gas Clearance

B1.1.5

Suitable Casting Materials for GDC

B1.1.6

Permanent Mold Casting Machines

B1.1.7

Selection of Mold Material

B1.1.8

Gravity Die Casting Mold Life

B1.1.9

Principle of Mold Design

B1.1.10

Solid Graphite Permanent Mold

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TG-2

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B1.1.1

CHAPTER: B1 GRAVITY DIE CASTING

TG-2

INTRODUCTION

This is a casting process in which the mould is permanent and same can be repeatedly used for making thousands of identical components.

B1.1.2

PERMANENT MOULD/GRAVITY DIE CASTING

In permanent mold casting, a metal mold consisting of two or more parts is repeatedly used for production of many castings of the same from The liquid metal enters the mold by gravity Simple removable cores are usually made of metal, but more complex cores are made of sand or plaster when sand or plaster cores are used , the process is called semi permanent mold casting. Permanent mold casting is particularly suitable for the high -volume production of castings with fairly uniform wall thickness and limited under -cuts or intricate internal coring. The process can also be used to produce complex castings, but production quantities should be high enough to justify the cost of the molds. Compared to sand casting, permanent mold casting permits the production of more uniform castings with closer dimensional tolerances, superior surface finish, and improved mechanical properties.

B1.1.3

LIMITATIONS OF PERMANENT MOULD CASTING

Permanent mold casting has the following limitations: § § § §

Not all alloys are suitable for permanent mold casting Because of relatively high tooling costs, the process can be prohibitively expensive for low production quantities Some shapes cannot be made using permanent mold casting, because of parting line location undercuts, or difficulties in removing the casting from the mold Coatings are required to protect the mold from attack by the molten metal

Metals that can be cast in permanent molds include the aluminum, magnesium, zinc and copper alloys and hypereutectic gray iron.

B1.1.4

PRINCIPLE OF PERMANENT MOULD CASTING

Compared with permanent mould casting, Die Casting can be made to closely dimensional limits and with thinner sections, holes can be cored, are produced, higher rates with less manual labor, have smoother surfaces and usually cost less per die casting. Permanent mould casting involves some what lower tooling cost, can be made with sand cores yielding shapes not available in die casting.

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CHAPTER: B1 GRAVITY DIE CASTING

TG-2

In permanent mould casting, a metal mold consisting of two or more parts is used repeatedly for producing many castings of the same form. The liqui d metal enters the mould by gravity. (The process does not, however, include pouring of ingots in metal moulds). Simple cores area made of metal, but more complex cores are made of sand or plaster. When sand or plaster cores are used, the process is called Semi permanent mold casting.

Removal of Casting from Molds: After a casting has solidified, the mold is opened and the casting is removed. To facilitate release of the casting from the mold, a lubricant is often added to the mold coating. The use of as much drafts as permissible on all portions of the casting makes ejection easier. For many castings, ejector pins or pry bars must be used. Core pins and cores should be designed so as not to interfere with removal of castings from the mold.

B1.1.4 (a)

PROGRESSIVE SOLIDIFICATION

Casting requires a feeding system whic h consists of gates, runners, risen etc. Risers must be connected to heavy section of the casting. The process of solidification must be in such manner that the casting freezes from the further most point progressively towards the risers. If this principle is not satisfied, shrinkage, porosity, cavitations or surface depressions can occur which may causes the rejection of the component.

B1.1.4 (b)

MINIMUM TURBULENCE

This principle must be observed during the filling of die cavity with molten metal. Turbulent filling of die will leave air bubbles and oxide films entrapped within the casting. The turbulence can be controlled by suitably designing the runner system. This principle must be satisfied for setting a sound casting.

B1.1.4 (c)

AIR AND GAS CLEARANCE

For gravity die casting the care must be given to air and gas clearance otherwise entrapped air or gas will cause defects in the components (blow holes, surface depression etc)

B1.1.5

SUITABLE CASTING METALS FOR GDC

Metals that can be cast in perma nent moulds include aluminum, magnesium, zinc and copper alloys, and hypereutectic gray iron.

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CHAPTER: B1 GRAVITY DIE CASTING

TG-2

Aluminum alloys : - Aluminum alloys have low density, which combined with their oxide-film-forming characteristics, make them flow some what sluggishly. The shrinkage of aluminum alloys during solidification is relatively large, and provision must be made for ample metal feed during solidifi cation. After solidification, aluminum alloys are soft at elevated temperature, and castings may distort during removal from the mold.

Magnesium alloys : - Magnesium alloys are less castable than aluminum alloys, and have relatively poor feeding characteri stics in thin -wall castings. Also, the castings are more sensitive to hot shortness (brittleness at elevated temperature) than are aluminum alloys castings. Generous fillers are required when the casting contains large bosses or when one section of the cas ting is much larger than another. Sharp casting detail cannot be obtained with magnesium alloys, and shapes that shrink on to mold sections are susceptible to cracking and should be avoided.

Copper alloys : - Copper alloys solidify at high temperatures, an d some have narrow solidifications ranges. They shrink on to cores and other mold elements, and shrink on to cores and other mold elements, and must be ejected from molds as soon as possible.

Zinc alloys: - Zinc alloys can be cast in permanent molds, but because the castings are usually made in large quantities, they are more often die cast.

Gray iron: - Gray iron is used successfully in high -volume production of small (28 g to

13.5 kg, or 1 oz to 30 lb), simple castings. However, more complex gray iron c astings, with internal coring and marked changes in section, have also been successfully made by the permanent mold process.

Maximum Size of Casting: Practical sizes of permanent mold castings are limited by cost. The maximum sizes that have been cast differ among the casting alloys.

Aluminum alloys: - In high production, permanent mold castings weighing up to 13.5 kg (30 lb) are made from aluminum alloys in casting machines. However, much larger castings can be produced.

Magnesium alloys: - It despite their comparatively low cast ability; have been cast in

permanent or semi -permanent molds to produce relatively large and complex casting. For instance, 8 kg (17.7 lb) housing for an emergency power unit was poured from alloy AZ91C in a semi -permanent mold. The mold utilized vertical parting and an oil -sand core to develop the vanes and internal surfaces of the casting. Surface finish of the casting varied from 6.4 to 12.7mm (250 to 500min.).

Copper alloy: - These permanent molds casting weighing over 9 kg (20 lb) rarely can be justified.

Gray iron: - Production of gray iron castings in permanent mold is seldom practical when the castings weigh more than 13.5 kg (30 lb).

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B1.1.6

CHAPTER: B1 GRAVITY DIE CASTING

TG-2

PERMANENT MOLD CASTING MACHINES

Permanent mold casting machines can be customized to automatically or manually operating. They are basically simple in construction.

Manually operated machine: Manually operated permanent mold casting machines may consists of a simple “book” mold arrangement, such as that shown in fig.1 or for castings with high ribs or walls that require mold retraction without rotation, the machine shown in fig. 2 can be used. With Either type of machine, after the casting solidified the mo ld halves are separated by manually releasing the eccentric mold clamps.

Automatic machines: For high-volume production, the manual drives are replaced by two -way hydraulic mechanisms. These can be programmed to open and close in a preset cycle. Thus, except for pouring of the metal and removal of castings, the operation is automatic. A method of permanent mold casting has been developed in which the metal is not ladled by hand. This is called the Wessel Process . The equipment for which is shown in fig. 3. In this method, the permanent mold is mounted on rails against the end face of the tilting reverberate furnace. As the furnace is tiled about an axis bear its center of gravity, metals flows through a pouring hole in ht wall of the furnace in the mold. The assembly remains in its tilted position for a predetermined interval, then returns to the s tarting position. Tilting is done by means of a hydraulic cylinder. .

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CHAPTER: B1 GRAVITY DIE CASTING

TG-2

Molds are parted vertically, parallel to the direction of metal flow. One mold half slides on the mounting rails; the other, which is hinged, swings away from the mounting rails, pulling the casting and sprue with if to leave the pouring hole clear for the next cycle. Core manipulation and casting ejection are the same as in conventional practice.

B1.1.7

SELECTION OF MOULD MATERIALS

Four principle factors affect the selection of material

s for permanent molds and

cores: § § § §

The pouring temperature of the metal to be cast The size of the casting The number of castings per mold Cost of the mold material

Mould Materials: - As indicated in Table A, gray iron is the most commonly used mold material. Aluminum or graphite molds are sometimes used for the small -quantity production of aluminum and magnesium castings, and graphite or carbon linear on steel are sometimes used for molds for casting copper alloys ( see also the section “Solid Graphite Molds” in this article). With aluminum or magnesium casting alloys, it is not unusual to obtain 100,000 castings, or more, per mold; however, molds for copper or gray iron casting alloys have a shorter life because of the higher pouring temperatures required. Pouring temperatures for specific metals are as follows:

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CHAPTER: B1 GRAVITY DIE CASTING

TG-2

TEMPERATURE, °C (°F) 465-620 (870-1050) 675-790 (1250-1450) 705-790 (1300-1450) 980-1230 (1800-2250) 1275-1355 (2325-2475)

METAL/ALLOY Zinc Aluminum Magnesium Copper Gray Iron

Gray iron molds without tool steel inserts are satisfactory for long production runs of aluminum and magnesium castings that will be magnesium casting that be machined extensively and for which s urface finish is not a major consideration. In the casting of zinc, well over 00.000 pours are possible in a gray iron mold (die casting is usually selected to produce zinc castings such large quantities).

Mold Inserts: - Full or partial mold cavities ins erts of the same material as the mold , or

of a different material, are sometimes used to obtain longer mold life, or to simplify machining handling or replacement. Inserts can also be used for venting, cooling thin walls, and heating portions of the mold o r the full cavity area . Inserts made of cast -to-shape gray iron are used for casting complex alu minum and magnesium parts that r ange in surface area from 320 to 2900 cm 2 (50 to 50 in. 2). Tolerance on these parts range from 0.76 to ± 1.5 mm (± 1.5 mm ± 0. 030 to ± 0.060 in.). Inserts last for 5000 to 20.000 pours, depending on casting complexity.

Core Materials: - Core materia ls are recommended in Tables B and C on the basis of performance over a wide range of coring requirement for small and large cores. An expendable core is used when the location or shape of the core does not permit its removal from the casting or when an in tricate design can be obtained at less cost with materials for such cores. These materials are listed below in order of increasing preference: § § §

Sand (oil – bonded or resin –bonded, shell, car bon dioxide-silicate) Plaster Graphite and carbon

Casting alloy

Table A recommended permanent mold Materials No. of Pours 1000 10,000

100,000

for small Castings (25 mm or 1inch Maximum dimension) Zinc Aluminum Mg.

Gray Iron: 1020steel Gray Iron: 1020steel

Copper

Gray Iron

Gray Iron

Gray IronGray (a) Iron (a)

Gray Iron: 1020steel Gray Iron: 1020steel Gray Iron

Gray Iron: 1020steel Gray Iron with AISI-H14 inserts: 1020steel Alloy Cast Iron

Quantity not Poured

for medium and large castings (upto 915mm or 36Inch maximum dimension) Zinc Aluminum Mg. Copper

Gray Iron (a)

Gray Iron:AISI-H11 (b)Gray Iron: AISI-H11 (b) Gray Iron Gray Iron Alloy Cast Iron

Alloy Cast Iron

Gray Iron (a)

Quantity not Poured

-8

Gray Iron: AISI-H11 (b) Gray Iron with AIS-H11/H1(c) inserts: 1020steel Alloy Cast Iron (d)

INDO-GERMAN TOOL ROOM, AHMEDABAD -916 DIE CASTING THEORY

CHAPTER: B1 GRAVITY DIE CASTING

TG-2

Table B Recommended Materials for small cores (