The first step in the injection moulding process is to manufacture a mould tool. This is a precision machined part (or assembly of parts) that contains the cavity - or cavities - the same shape as the finished part. The mould tool is unique for every component, but can be used many times. Tooling costs are usually quite high; therefore, economies of scale dictate that injection moulded parts are required in high quantities.
A mould tool is clamped into an injection moulding machine. At the other end of the machine, plastic granules are fed into a heated cylinder and a reciprocating screw therein moves the plastic, which melts into the mould under pressure. When the plastic hardens, the clamping unit opens so the final component can be removed. The process is then repeated.