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During the moulding process, it may be that you would like to incorporate other materials in the design to create the finished prototype. This is undertaken by adding ‘inserts’ into the mould prior to the injection of the resin, which remain when the part is ejected at the end of the process. Depending on the quantity of prototypes being produced, this can be undertaken by either human operators or robots and is an efficient way to add other materials into the final design, whilst retaining the economies of injection moulding.

In order to successfully produce a part with an insert, it is important to choose the initial resin material carefully, so that it will be compatible with the insert that you would like to use. Generally, most resins, including Polycarbonate, Polypropylene and ABS will be suitable for use with an insert, with the insert itself usually being constructed by metal or plastic. The material used for the insert is generally more hard-wearing than the resin that it is being placed into and this ensures longevity and a reduced likelihood that it will fail during use.

There are multiple processes used in insert moulding, but the main ones are:

Metal Screw-In: As discussed above, the metal insert is required to be constructed of a more hard wearing material than the resin in which it is being placed. The action of screwing and unscrewing requires that this is the case, otherwise the part may fail.

Continuous Film: This technique incorporates a pre-printed plastic film which is drawn over the part in order to create a seal, for example in the packaging of food items.

Labels: Labels are introduced into the mould at strategic points and at set times during the moulding process. These adhere to the resin through electrostatic charging of the labels and the tool itself.

Finally, it is important to note the each insert can be placed anywhere in the mould and they do not have to align themselves with any particular joint or corner. Due to the nature of the design, it is important to remember that they must be removed at the end of the moulding process and so this needs to be taken into account when designing the part and mould in the initial stages.