CASTING - MANUFACTURING PROCESS BASIC INFORMATION


It is one of the most important manufacturing process used in Mechanical Engineering. The castings are obtained by remelting of ingots* in a cupola or some other foundry furnace and then pouring this molten metal into metal or sand moulds.

The various important casting processes are as follows:
1. Sand mould casting. The casting produced by pouring molten metal in sand mould is called sand mould casting. It is particularly used for parts of larger sizes.

2. Permanent mould casting. The casting produced by pouring molten metal in a metallic mould is called permanent mould casting. It is used for casting aluminium pistons, electric iron parts, cooking utensils, gears, etc.

The permanent mould castings have the following advantages:
(a) It has more favourable fine grained structure.
(b) The dimensions may be obtained with close tolerances.
(c) The holes up to 6.35 mm diameter may be easily cast with metal cores.

3. Slush casting. It is a special application of permanent metal mould casting. This method is used for production of hollow castings without the use of cores.

4. Die casting. The casting produced by forcing molten metal under pressure into a permanent metal mould (known as die) is called die casting. A die is usually made in two halves and when closed it forms a cavity similar to the casting desired.

One half of the die that remains stationary is known as cover die and the other movable half is called ejector die. The die casting method is mostly used for castings of non-ferrous metals of comparatively low fusion temperature.

This process is cheaper and quicker than permanent or sand mould casting. Most of the automobile parts like fuel pump, carburettor bodies, horn, heaters, wipers, brackets, steering wheels, hubs and crank cases are made with this process.

Following are the advantages and disadvantages of die casting :

Advantages of Die Casting
(a) The production rate is high, ranging up to 700 castings per hour.
(b) It gives better surface smoothness.
(c) The dimensions may be obtained within tolerances.
(d) The die retains its trueness and life for longer periods. For example, the life of a die for zinc base castings is upto one million castings, for copper base alloys upto 75 000 castings and for aluminium base alloys upto 500 000 castings.
(e) It requires less floor area for equivalent production by other casting methods.
( f ) By die casting, thin and complex shapes can be easily produced.
( g) The holes up to 0.8 mm can be cast.

Disadvantages Die Casting
(a) The die casting units are costly.
(b) Only non-ferrous alloys are casted more economically.
(c) It requires special skill for maintenance and operation of a die casting machine.

5. Centrifugal casting. The casting produced by a process in which molten metal is poured and allowed to solidify while the mould is kept revolving, is known as centrifugal casting. The metal thus poured is subjected to centrifugal force due to which it flows in the mould cavities.

This results in the production of high density castings with promoted directional solidification. The examples of centrifugal castings are pipes, cylinder liners and sleeves, rolls, bushes, bearings, gears, flywheels, gun barrels, piston rings, brake drums, etc.

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2 comments:

matiworld said...

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matiworld said...

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