Injection moulding is one of the most popular manufacturing processes, used for fabrication of plastic parts. The plastic parts, produced by this method, can have variable shapes and sizes.
The injection moulding process requires the following to be present: an injection moulding machine, raw plastics material and a mould. Many types of injection moulding machines are available, with different components and configurations.
All machines have some common parts, these are:
– injection unit,
– mould assembly unit,
– clamping unit.
The injection unit is composed of a motor, material hopper, barrel and a screw. The barrel has heaters and is ended with a nozzle.
The mould assembly is composed of a mould (core and cavity), bars, stationary platen and an ejection system.
The clamping unit contains a motor, movable platen and bars.
The mould is a very expensive part and consequently the injection moulding process is mostly used in mass production (thousands or millions of parts). Typically, moulds are made of hardened or pre-hardened steel or aluminium.
How does it work?
The injection process is divided into the following stages:
1. Clamping – the movable and stationary platens hold the cavity and the core together under pressure during the injection (and later also during cool down).
2. Injection – the plastic material is melted in the barrel and is being moved towards the nozzle. The required amount of the plastic (called shot) is injected into the mould very quickly.
3. Cooling – the molten plastic in the mould is being cooled down, keeping the desired shape.
4. Ejection – the cooled part is ready, the mould opens and the ejecting system ejects the part from the mould.
Simple, isn’t it?