What is Mould ?

Mould: A hollow form or cavity into which molten plastic is forced to give the shape of the
required component. The term generally refers to the whole assembly of parts that make up
the section of the molding equipment in which the parts are formed. Also called a tool or die.

Moulds separate into at least two halves (called the core and the cavity) to permit the part to

be extracted; in general the shape of a part must be such that it will not be locked into the

mould. For example, sides of objects typically cannot be parallel with the direction of draw

(the direction in which the core and cavity separate from each other). They are angled

slightly; examination of most household objects made from plastic will show this aspect of

design, known as draft. Parts that are "bucket-like" tend to shrink onto the core while cooling

and, after the cavity is pulled away, are typically ejected using pins. Parts can be easily

welded together after moulding to allow for a hollow part (like a water jug or doll's head) that

couldn't physically be designed as one mould.

More complex parts are formed using more complex moulds, which may require moveable
sections, called slides, which are inserted into the mould to form particular features that
cannot be formed using only a core and a cavity, but are then withdrawn to allow the part to
be released. Some moulds even allow previously moulded parts to be re-inserted to allow a
new plastic layer to form around the first part. This system can allow for production of fully
tyred wheels.


Traditionally, moulds have been very expensive to manufacture; therefore, they were usually
Molds require: Engineering and design, special materials, machinery and highly skilled workers.