Mould design

Mould design
A mould may have one cavity or several, even as many as 100, depending largely on part
size. Multi-cavity moulds normally produce identical parts, though one type, known as a
family mould is used to make assortment of parts later assembled as a single
Object.
The main structural mechanism of a mould are the mould plates, which, with the aid of
pins and bushings, lock together to support and align the internal working parts of the
mould.

In operation, one mould half remains in a fixed position on the moulding machine while
the other is moved to and from the fixed half to bring off mould closing and opening.
The fixed half of the mould contains a system of channels for delivery of melted resin to
the mould cavity. This system consists of an entry port sprue which couples with
passages runners that convey resin from the sprue to the entrance way 'gate' of the
cavity. The part ejection mechanism is usually installed in the moving half of the mould.
Moulds are equipped with a cooling system designed to withdraw heat from the melted
resin in the cavity and thus cause the part or parts to soldify. Rapid cooling reduces
machine cycle time and accelerates production, while uniformity in the rate of cooling
throughout a part prevents warpage or undue shrinkage. Uniform part cooling requires
that the most concentrated cooling take place in the vicinity of the hottest areas of the
cavity.