INJECTION MOULDS

What's a Plastic Injection Mould?

As the name suggests a plastic injection mould is a mould  into which molten plastic is injected to form a specific shape or part.  Other names for plastic injection moulds are 'tools' or 'dies'.

You don't have to look far to find something that is a product of injection moulding.  Your computer mouse, the keyboard keys you're tapping and your plastic biro, the casing for your phone, printer and fax are all plastic injection moulded.  No doubt your lunch today was packed in an injection moulded lunch box and when you hop into the car to drive home you'll put on your  plastic framed sunglasses, turn on the stereo with the plastic injection moulded buttons and adjust the plastic vents on the air-conditioning. 

Simply a plastic injection mould is a series of steel plates and guide pins.  These plates are assembled in two halves, a fixed and moving half.  Each half contains a cavity and core which have been machined so that when the two halves come together a cavity (or hollow) is formed in the shape of the required plastic part.   The core determines the internal dimensions of the plastic part so that the part is not solid plastic.  The mould is fixed into an injection moulding machine where molten plastic is pumped into the cavity to form the plastic part.  When the plastic cools and solidifies the two halves come apart and the plastic part is ejected.

The process of mould-building is however, more complex than the description above and each mould varies according to the part being produced.  For example if a part has an internal thread, like an irrigation fitting that is screwed onto a pipe, the mould will be built with an auto-unscrewing component.  A six-cavity (produces 6 parts at once) auto-unscrewing tool to produce a fitting to suit 25mm pipe (no bigger than a tennis ball) takes about 600 hours to make. 

Injection moulds are manufactured by qualified toolmakers who must complete a four year apprenticeship.