The first step in the injection moulding process is to manufacture a mould. The mould is unique for every component, but can be used many times. Some moulds has service life of many hundreds of thousands parts. Normally, the mould can be manufactured using machining or using wire or spark erosion.
When the mould is manufactured, it is clamped in the injection moulding machine. The clamping unit simply keeps the mould together. In the other end of the machine plastic granulates are fed into a heated cylinder which forces the plastic, which melts, into the mould under pressure. When the plastic hardens, the clamping unit opens so the final component can be removed.
There is a few aspects that determine which injection moulding job is suitable for a certain machine. The most important factor is the press force, simply the force with which the melted plastic is forced into the mould. A too weak force will end in a badly produced component, and a too strong force is uneconomical. There are also other factors to weigh in, such as length, width and depth, appropriate temperatures and cooling times. Injection moulding is suitable for medium to large sized batches as the initial cost for a mould is high but the the cost for every component is low.
Picture: Frontier Design Ltd