Knowledge Institute of Technology, Salem.

Department of Mechanical Engineering

MANUFACTURING

TECHNOLOGY I

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Casting

• A material in a liquid or semisolid form is poured or forced to flow into a die cavity and allowed to solidify, thus taking the solid shape of the cavity

• The process can be applied on metals and plastics

• The term casting is commonly used for metals and the term molding is used for plastics

• Examples: door handles, locks, the outer casing or housing for motors, pumps, etc., wheels of many cars. Casting is also heavily used in the toy industry to make parts, e.g. toy cars, planes, etc.

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CASTING PROCESS

Steps involved in casting process

• Pattern making.

• Mould making.

• Core making.

• Melting of metal and pouring.

• Cooling and solidification

• Cleaning of castings and inspection

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Pattern • Pattern: A Pattern is a model or the replica of the object to be

cast. Except for the various allowances a pattern exactly resembles the casting to be made. Patterns may be in two or three pieces, where as casting are in a single piece. A pattern is required even if one object has to be cast. The quality of casting and the final product will be effected to a great extent by the planning of pattern. M

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PROPERTIES OF PATTERN MATERIAL • It should be easily shaped, worked, machined and joined.

• It should be resistant to wear and corrosion.

• It should be resistant to chemical action.

• It should be dimensionally stable and must remain unaffected by variations in temperature and humidity.

• It should be easily available and economical

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WOOD • These are used where the no. of castings to be produced is small

and pattern size is large.

Advantages:

• Easily available ,Low weight ,Low cost

Limitations: Susceptible to shrinkage and swelling Possess poor wear resistance Abraded easily by sand action Absorb moisture, consequently get wrapped Cannot withstand rough handling Life is very short.

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METAL

• These are employed where large no. of castings have to be produced from same patterns.

Advantages:

• Do not absorb moisture

• More stronger Possess much longer life

• Do not wrap, retain their shape Greater resistance to abrasion

• Accurate and smooth surface finish Good machinability

Limitations: Expensive Require a lot of machining for accuracy Not easily repaired Ferrous patterns get rusted Heavy weight , thus difficult to handle

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PLASTIC

Advantages: Durable Provides a smooth surface Moisture resistant Does not involve any appreciable change in size or shape

• Light weight Good strength

• Wear and corrosion resistance Easy to make Abrasion resistance

• Good resistance to chemical attack

Limitations: Plastic patterns are Fragile These are may not work well when subject to conditions of severe shock as in machine molding (jolting).

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POLYSTYRENE • Used for prototype (single piece) castings

• Also known as Disposable patterns

Advantages: Provide very good surface finish. Impart high accuracy to castings.

After being molded, the wax pattern is not taken out of the mould like other patterns; rather the mould is inverted and heated; the molten wax comes out and/or is evaporated. Thus there is no chance of the mould cavity getting damaged while removing the pattern. Wax patterns find applications in Investment casting process.

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Plaster Patterns

Advantages: It can be easily worked by using wood working tools.

• Intricate shapes can be cast without any difficulty.

• It has high compressive strength. Plaster may be made out of Plaster of paris or Gypsum cement.

• Plaster mixture is poured into a mould made by a sweep pattern or a wooden master pattern, in order to obtain a Plaster pattern.

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Types of Patterns 1. Solid or single piece pattern

2. Split or two piece pattern

3. Match plate pattern

4. Skeleton pattern

5. Loose-piece pattern

6. Sweep pattern

7. Segmental pattern

8. Shell pattern

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Solid or single piece pattern

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Split or two piece pattern

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Match plate pattern

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Skeleton pattern

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Loose-piece pattern

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Sweep pattern

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Segmental pattern

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Shell pattern

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pattern Materials

1.Wood

2.Metals

3.Plaster

4.Plastics

5.Wax

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pattern Allowances 1. Shrinkage allowance or Contraction allowance

2. Machining allowance or Finishing allowance

3. Draft allowance

4. Rapping or Shake allowance

5 Distortion or Camber allowance

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IMPORTANT TWO MARKS SO FOR…. • Name the steps involved in making a casting

• What are the applications of casting?

• Define pattern

• Define mould making.

• Why is a pattern larger than casting?

• Name the functions of pattern.

• Name the materials for making patterns

• List the allowances of pattern

• Name any four types of pattern

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Shrinkage Allowance

• All most all cast metals shrink or contract volumetrically on cooling.

• The metal shrinkage is of two types:

1. Liquid Shrinkage: it refers to the reduction in volume when the metal changes from liquid state to solid state at the solidus temperature.

2. Solid Shrinkage: it refers to the reduction in volume caused when metal loses temperature in solid state.

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Machining Allowance

• A Casting is given an allowance for machining, because:

Castings get oxidized in the mold and during heat treatment; scales etc., thus formed need to be removed.

It is the intended to remove surface roughness and other imperfections from the castings.

It is required to achieve exact casting dimensions. Surface finish is required on the casting

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How much extra metal or how much machining allowance should be provided

• Nature of metals. Size and shape of casting. The type of machining operations to be employed for cleaning the casting. Casting conditions. Molding process employed

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Draft allowance

• It is given to all surfaces perpendicular to parting line.

• Pattern can be easily removed

The amount of taper depends upon:

• Shape and size of pattern in the depth direction in contact with the mould cavity.

• Moulding methods.

• Mould materials.

Draft allowance is imparted on internal as well as external surfaces; of course it is more on internal surfaces.

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Distortion or cambered allowance

A casting will distort or wrap if :

• It is of irregular shape, All it parts do not shrink uniformly i.e., some parts shrinks while others are restricted from during so,

• It is u or v-shape, The arms possess unequal thickness

• It has long, rangy arms as those of propeller strut for the ship, It is a long flat casting, One portion of the casting cools at a faster rate as compared to the other.

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Shake allowance

• A patter is shaken or rapped

• Pattern a little is loosened in the mold cavity and can be easily removed.

• Hence, a –ve allowance is provided on the pattern i.e., the pattern dimensions are kept smaller in order to compensate the enlargement of mould cavity due to rapping. The magnitude of shake allowance can be reduced by increasing the tapper

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Core Boxes 1. Half core box

2. Dump core box

3. Split core box

4. Strickle core box

5 Gang core box

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Half core Box

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Dump core Box

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Split core Box

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Strickle core Box

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Gang core Box

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moulding Tools 1. Shovel

2. Riddle

3. Rammers

4. Trowels

5. Mallet

6. Bellows and etc..

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Shovel

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Riddle

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Rammers

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Trowel

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Mallet

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Mallet

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Co2 Process

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Types of cores 1. Horizontal core 2. Vertical core 3. Balanced core 4. Hanging core 5. Cover core 6. Wing core 7. Ram-up core 8. Kiss core

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Horizontal core

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Vertical core

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Balanced core

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Hanging core

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Wing core

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Ram-up core

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Types of Moulding

1. Green sand moulding

2. Dry sand moulding

3. Loam Moulding

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Green sand moulding

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Loam moulding

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Moulding Machines

1. Jolt machine

2. Squeezing machine

3. Sand slinger

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Moulding Machine

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Induction type Electric furnace

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Hot chamber die casting machine

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Cold chamber die casting machine

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Gravity die casting

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Centrifugal casting

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Continuous casting

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