• Injection moulding is a manufacturing process for producing parts by injecting material into a mould.
• Injection moulding can be performed with a host of materials, including metals, glasses, elastomers, confections, and most commonly thermoplastic and thermosetting polymers.
• Material for the part is fed into a heated barrel, mixed, and forced into a mould cavity, where it cools and hardens to the configuration of the cavity.
• After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mould maker (or toolmaker) from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part.
• Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars. Advances in 3D printing technology, using photopolymers which do not melt during the injection moulding of some lower temperature thermoplastics, can be used for some simple injection moulds.

Process

• Small injection moulder showing hopper, nozzle and die area
• With injection moulding, granular plastic is fed by gravity from a hopper into a heated barrel. As the granules are slowly moved forward by a screw-type plunger, the plastic is forced into a heated chamber, where it is melted.
• As the plunger advances, the melted plastic is forced through a nozzle that rests against the mould, allowing it to enter the mould cavity through a gate and runner system.
• The mould remains cold so the plastic solidifies almost as soon as the mould is filled.

Injection moulding cycle

• The sequence of events during the injection mould of a plastic part is called the injection moulding cycle.
• The cycle begins when the mould closes, followed by the injection of the polymer into the mould cavity.
• Once the cavity is filled, a holding pressure is maintained to compensate for material shrinkage.
• In the next step, the screw turns, feeding the next shot to the front screw. This causes the screw to retract as the next shot is prepared. Once the part is sufficiently cool, the mould opens and the part is ejected.