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The Injection Moulding-Mould


A mould used for Injection Moulding may cost thousands of pounds to produce however it does turn out to be economical as many thousands of mouldings can be produced from a single mould. This results in the low cost of each moulding.

It used to be the case that when a new type of casting was needed a brand new die had to be made. Modern dies and moulds are made from a number of interchangeable parts. This allows the shape of the mould to be altered.

The dies or moulds used in this process are made from alloy stainless steel. These special alloy steel moulds are made in a number of parts to allow the mouldings to be easily removed.

These steel moulds are initially very expensive to make and are suited to production in quantity where accuracy of size, shape and surface finish is essential.


Important Features of the Die

It is important that the mould can be easily opened and the moulding easily ejected. A slot can often be made along the joint line of the mould so that a screwdriver can be inserted and turned to separate the parts.

Deep shapes must be tapered to help with the removal of the moulding and ejector pins are usually built into the mould to push the moulding out.

All moulding cavity surfaces must be smooth and highly polished to ensure a good quality of finish to the mouldings.

Sharp corners and sudden changes in wall thickness should be avoided because the interrupt the flow of plastic and weaken the mouldings.

Large flat surfaces should be avoided because the finished mouldings will often not come out completely flat.

The image on the right shows the ejector pins protruding from the one half of the mould. The moulding has been ejected and is missing from the image.

Image: Courtesy of Focus Educational.