Injection Moulding
Injection moulding is a manufacturing technique for making parts from both thermoplastic and thermosetting plastic materials in production. Molten plastic is injected at high pressure into a mould, which is the inverse of the product's shape. After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mouldmaker (or toolmaker) from metal, usually either steel or aluminium, and precision-machined to form the features of the desired part. Injection moulding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars. Injection moulding is the most common method of production, with some commonly made items including bottle caps and outdoor furniture. Injection moulding typically is capable of tolerances equivalent to an IT Grade of about 9-14.
Standard two plates tooling - core and cavity are inserts in a mould base - "Family mould" of 5 different parts.
The most commonly used thermoplastic materials are:
- PS -polystyrene (low cost, lacking the strength and longevity of other materials),
- ABS -acrylonitrile butadiene styrene (a ter-polymer or mixture of compounds used for everything from Lego parts to electronics housings),
- PA -polyamide (chemically resistant, heat resistant, tough and flexible - used for combs),
- PP-polypropylene (tough and flexible - used for containers),
- PE -polyethylene,
- PVC -polyvinyl chloride (more common in extrusions as used for pipes, window frames, or as the insulation on wiring where it is rendered flexible by the inclusion of a high proportion of plasticiser).
Injection moulding can also be used to manufacture parts from aluminium or brass (die casting). The melting points of these metals are much higher than those of plastics; this makes for substantially shorter mould lifetimes despite the use of specialised steels. Nonetheless, the costs compare quite favourably to sand casting, particularly for smaller parts.
