Injection Moulding

What is Injection Moulding?

The injection moulding process is very similar to casting, but primarily uses plastic as the raw material instead of metals. The plastic is melted and injected into moulds and; when cooled, will solidify to form the desired shape.

Is is typically used for mass production due to it’s high repeatability rate to produce thousands of identical items.

Injection Moulding Machine

Injection Moulding Process

Making the Moulds

The first part of the injection moulding process is the design and manufacture of the mould, or die, which will be used throughout the manufacture of the parts.

Simple moulds can be created through CNC machining/milling operations, but more complex mould designs would be made through EDM/Spark Erosion.

The moulds themesleves consists of 2 halves: an injection mould (where the molten material is inserted) and an ejector mould (the final part remains on the ejector mould side and freely falls when ejected).

Injection Moulding Process
User:Brockey, CC BY 3.0 , via Wikimedia Commons

Injection Process

The material, usually in the form of pellets or granules, is fed into the material hopper which drops the material into a heated barrel. This is forced into a heated chamber which fully melts the material.

The mould is closed before the melted material is fed through a series of nozzles into the mould cavity.

As the mould is kept cold, the material solidifies almost as soon as the mould is filled; so the part can be ejected from the mould quickly and the process can repeat.

Examples of Plastic Parts