Plastic injection moulding is the most common way to manufacture plastic parts in volume. Here's how it works, in plain English.
The Basic Process
Plastic granules are heated until molten, then injected under high pressure into a precision mould tool. The plastic fills the cavity, cools and solidifies into the shape of the part. The tool opens, the part is ejected, and the cycle repeats, often in seconds.
Because the same tool produces the same part every cycle, injection moulding delivers excellent consistency at a low cost per part.
What Is the Mould Tool?
The mould tool is the precision-machined metal block that shapes the plastic. It's the heart of the process and the biggest single factor in part quality and cost. Learn more in What Is Mould Tooling?
What Is It Used For?
Almost any plastic part made in quantity: housings, clips, gears, caps, components and assemblies across medical, automotive, food and many other sectors.
Why Is It So Popular?
Once tooling exists, parts can be produced quickly, repeatably and cheaply, with great consistency and a wide choice of materials and finishes. That combination is hard to beat for volume production.
Sources & Further Reading
For independent background on the process, see the British Plastics Federation's guide to injection moulding and the overview on Wikipedia.