Types of Casting Processes

What are different types of casting processes? The sand moulds may be used for casting ferrous and non-ferrous metals, but these moulds can be used only once, because the mould is destroyed after the metal has solidified. This will increase the cost of production. The sand moulds also, cannot maintain better tolerances and smooth surface finish. In order to meet these requirements, following casting methods may be used:

1. Permanent mould casting

A casting made by pouring molten metal by gravity into a mould made of some metallic alloy or other material of permanence is known as permanent mould casting. The term die casting is another name for this type of casting.

2. Slush casting

The slush casting is a special application involving the use of a permanent mould. It is used for casting low melting temperature alloys. This method is only adopted for ornaments and toys of non-ferrous alloys.

3. Die casting

The die casting (also known as pressure die casting) may be defined as that casting which uses the permanent mould (called die) and the molten metal is introduced into it by means of pressure. Following are the two types of die casting machines commonly y used for die casting. ·

(a) Hot chamber die casting machine

In a hot chamber die casting machine, the melting pot is an integral part of the machine. The molten metal is forced in the die cavity at pressures from 7 to 14 MPa. The pressure may be obtained by the application of compressed air or by a hydraulically operated plunger. The hot chamber die casting machine is used for casting zinc, tin, lead and other low melting alloys.

(b) Cold chamber die casting machine

In a cold chamber die casting machine, the melting pot is usually separate from the machine and the molten metal is transferred to injection mechanism by ladle. The pressure on the casting metal in cold chamber die casting machine may vary from 21 to 210 MPa and in some cases may reach 700 MPa. This process is used for casting aluminum, magnesium, copper base alloys and other high melting alloys.

4. Centrifugal casting

A casting process in which molten metal is poured and allowed to solidify while the mould is revolving, is called centrifugal casting. The castings produced under this centrifugal force is called centrifugal casting. This process is especially employed for casting articles of symmetrical shape. The ferrous and nonferrous metals can be casted by this process. The castings produced by this process have dense and fine-grained structure.

5. Investment casting

It is also known as lost wax process or precision casting. The castings produced by this method are within n very close tolerances (+/- 0.05 mm) and do not require subsequent machining.

6. Shell moulding process

The shell moulding process is also called croning process. The shell cast parts can be produced with dimensional tolerances of +/- 0.2 mm.