Injection Moulding

Injection moulding is by far the most common process employed by designers for plastic products. This is because the dimensions and shapes can be accurately controlled and the process is very reliable in production. A diagram of the equipment required is shown below and should be familiar from your notes on extrusion.

The thermoplastic is fed from the hopper and forced through the heating units by an Archimedian screw. The molten plastic is then forced into mould, which, after sufficient cooling time, is opened and the product removed.
For mass-production, one injection moulding machine may inject the plastic into several moulds all feeding from a common sprue. Other processes include several injection moulding machines injecting different colours into a common mould. The range of objects produced by injection moulding range from the gearwheel of a wrist watch weighing 0.00056g to a 37kg garbage container.