The process and its implications
The majority of injection moulding machines are run fully automatically.
The polymer raw material in the form of powder or granules is fed into the machine where a rotating screw pushes it forwards while it is being heated up by external heating bands. When the material is fully molten it is forced (injected) into a hardened steel mould known as a tool. The tool is rapidly cooled and then opens on a split line to reveal the plastic moulding.
The tool may have a single cavity or have multiple cavities. For example, small items like bottle tops tend to be made in tools with over 100 identical cavities. The cavities can also be for different parts as was the case for the moulding illustrated (Starck 004253) which shows a product from such a tool with its parts still attached.
The set-up costs for injection moulding are high. However, as the products can be produced rapidly and with low labour costs, the cost of individual units is low provided they are produced in sufficient numbers.