First things first
What is plastic injection moulding?
It is a manufacturing process for producing parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, mixed, and forced into a mould cavity where it cools and hardens to the configuration of the cavity. 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.
The moulding process in 4 simple steps
- Granulated or powdered thermoplastic plastic is fed from a hopper into the Injection Moulding machine.
- The Injection Moulding machine consists of a hollow steel barrel, containing a rotating screw (Archemidial Screw). The screw carries the plastic along the barrel to the mould. Heaters surround the barrel melt the plastic as it travels along the barrel.
- The screw is forced back as the melted plastic collects at the end of the barrel. Once enough plastic has collected a hydraulic ram pushes the screw forward injecting the plastic through a sprue into a mould cavity. The mould is warmed before injecting and the plastic is injected quickly to prevent it from hardening before the mould is full.
- Pressure is maintained for a short time (dwell time) to prevent the material creeping back during setting (hardening). This prevents shrinkage and hollows, therefore giving a better quality product. The moulding is left to cool before removing (ejected) from the mould. The moulding takes on the shape of the mould cavity.
Very informative 9 min video: