What is casting?

The cast­ing pro­cess is used to make com­plex shapes by pour­ing mol­ten metal into a mould. Parts that would be dif­fi­cult or uneco­nomic to make by other meth­ods can be pro­duced by cast­ing. Cast­ings are pro­duced from re-cycled metal and in this way the cast­ing pro­cess is able to take a waste product and turn it into new high value com­pon­ents, unend­ingly. The pro­cess offers unlim­ited scope in design.

There are two main cast­ing pro­cesses, one in which the mould is des­troyed as part of the pro­cess and one in which the mould may be re-used.
In sand cast­ing the hol­low mould is made of bon­ded sand using a wooden pat­tern, which is in the shape of the com­pon­ent to be made. Hol­low sec­tions can be intro­duced through the use of sand cores placed into the mould cav­ity. The pat­tern is removed and mol­ten metal is poured into the cav­ity. Once the metal has solid­i­fied, the sand mould and any cores are removed.
The pat­tern may be re-used and the sand can gen­er­ally be recycled.

In diecast­ing, the mould is made of metal and is called a tool or die. The mol­ten metal is intro­duced into the die by grav­ity or under low pres­sure or high pres­sure. The die may be re-used many thou­sands of times to pro­duced thou­sands of components.
Invest­ment cast­ing, in which a wax copy of the com­pon­ent is used to pro­duce a ceramic mould, has been in exist­ence for thou­sands of years, yet is still used to pro­duce large num­bers of high qual­ity cast­ings for aerospace and med­ical applications.
Other vari­ations of cast­ing pro­cesses include rapid pro­to­typ­ing, cent­ri­fu­gal cast­ing, con­tinu­ous cast­ing and pro­cesses in which a semi-solid metal bil­let is squeezed into the mould or die, e.g. rheocast­ing and thixoforming.
The choice of pro­cess is determ­ined by the num­ber of com­pon­ents required, the metal alloy to be cast, the price per part and prop­er­ties such as sur­face fin­ish, strength etc.