Contrary to simple punch or press forms used for the processing of sheet metal, injection moulds are a lot more complicated in their build up. In addition to the negative contour of the end product, injection moulds need to contain a variety of other components. Injection moulding is a thermal process. Therefore, the tool needs to contain sufficient cooling channels, otherwise the injected workpiece will not harden fast enough thus resulting in an inefficient production process. Air that is displaced from the injection moulding process must be able to escape. The negative shape of the workpiece needs to be fully poured out in seconds. The pouring channels are incorporated in the tool.
Finally, the workpiece needs to be removed from the tool. For this reason, every injection mould contains a built-in ejector. Cooling systems, material supply and an ejector means that the injection mould is a relatively complex system built out of hundreds of different individual parts. The price of an injection moulding tool can easy exceed the price of a second hand machine.