Shaping by reforming

Reforming is a method of shaping materials which changes their overall appearance by first melting or softening them into a paste, then hardening them. Reforming methods include casting, extrusion and injection moulding.

Casting

Most metals can be cast, but in school usually only aluminium is used.

1. Create the required shape in a soft material - usually wood. This is called a pattern.
2. Make a mould by placing the pattern in special casting sand inside a moulding box or flask. The sand is made to stick together using water or oil.
3. The pattern is removed and metal poured into the cavity.

Die casting

Die casting uses a metal mould which can be very detailed. The mould is made in two parts to allow the casting to be removed. Die casting is a very important industrial process used for many different types of products.

Die-cast aluminium engine parts     Injection-moulded plastic hardhat.

Extrusion

Extrusion is used to produce long, but fairly thin products such as pipes or curtain tracks. Both plastics and metal can be extruded. The material is forced through a die, which contains a hole which is the same shape as the required product.

Injection moulding

Injection moulding is a similar process to die casting. A metal mould is used and softened or molten plastic is forced into the mould by pressure from a screw thread or pneumatic plunger. The mould is made in two parts to allow the moulding to be removed. Polythene, polystyrene, polypropylene and nylon are the plastics most often used in injection moulding, which is used extensively in industry.