Posted on: 2nd Aug 2021
On the surface these two moulding processes may seem very similar, however there are distinct differences that should be taken into consideration when making production decisions.
In the injection moulding process, the chosen material is introduced into the injection moulding machine via a hopper. The virgin material starts the process in pellet form. The injection moulding machine consists of a heated barrel from which a reciprocating screw feeds the molten plastic into a temperature-controlled mould.
The screw melts the pellets and acts as a ram during the injection phase. The molten plastic is injected into a mould tool that has been manufactured to the specific design of the moulded part.
Once the part is moulded, the mould opens to release the part. This whole process is then repeated for the entirety of the production run.
After the moulding process, the parts are cooled, before being trimmed/finished if required.
Cast moulding is a manufacturing process where liquid polyurethane is poured into a heated mould. The material is thermoset and therefore the polymer is heat cured and, when solid, the moulded part is removed from the mould. Generally, moulds are open on one full side which means the poured face usually produces a flat surface. Therefore, some profile details may require additional machining/processing after moulding.
Due to the requirements of heat processing, moulds are warmed on a “hot plate” or within an oven system depending on the target temperatures of the mould/casting material and/or the mould size/profile. This setup/processing requirement is also dictated by the mould material;
Overall, neither manufacturing process is “better” than the other. The key is understanding each process to enable you to make an informed decision on which suits your specific needs the most.