Six Basic Factors in Casting Process

1. Mould Cavity:
While making a mould cavity with desired shape and size, one must keep in mind the shrinkage factor of the solidifying metal. The cavity must contain with in itself all complexity of shapes of the desired finished component. Selecting the right mould material is also very important as it must be capable of reproducing the desired detail. The mould material should not be affected significantly by the molten metal that it must contain. In case of expendable moulds, a new mould must be prepared for each casting. Whereas, reusable or permanent moulds can be used more than once. The latter type are made from such materials that can withstand repeated castings. The permanent moulds are very costly as these are made of metal or graphite and are used for large production runs. For smaller quantities production, the expendable moulds are generally preferred, simply because of their economical aspect.

 

2. Melting Process
The objectives of melting process are:
Providing molten material at the proper temperature.
Providing molten material in the desired quantity
Acceptable quality
Reasonable cost.

 

3. Pouring Techniques
It is a technique by which the moulds are filled in with molten metal. There must be provisions for air or gases inside the mould to come out when the molten metal is poured in. When the hot metal enters the mould cavity, it may generate various gases due to chemical reactions. The mould design should allow these gases to escape, so that the molten metal can spread and fill the mould cavity completely. It helps in producing defect free, fully dense and quality casting components.

 

4. Solidification Process
Better design and control at this stage helps in getting quality output. The mould design should be such that it put less restraint to the shrinkage that occurs during the cooling of metals. It helps in preventing any kind of crack on the casting when it is still hot and its strength is low. Moreover, the designers should also be careful about the fact that porosity or voids may occur during solidification and solidification shrinkage. A quality casting product should be free from these defects.

 

5. Mould Removal
After proper solidification, the casting should be removed from the mould. Generally, expendable moulds are broken apart and destroyed after each casting is produced without any difficulty. But, using re-usable moulds may cause major challenges from designers' point of view on the removal of casting from permanent moulds.

 

6. Cleaning, Finishing and Inspection
Various cleaning, finishing, and inspection operations are performed after the casting is removed from the mould. Extraneous material that is attached where the metal entered the cavity, excesses at mould parting lines, and mould material that is attached to the casting surface must all be removed.