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 mold cavity where it cools and hardens to the configuration of the cavity.:240 After a product is designed, usually by an industrial designer or an engineer, moulds are made by a mouldmaker (or toolmaker) from metal, usually either steel or aluminum, and precision-machined to form the features of the desired part. Advances in technology now also allow for 3D printing of injection moulds for certain applications, using photopolymer plastics which do not melt during the injection process. Injection moulding is widely used for manufacturing a variety of parts, from the smallest components to entire body panels of cars.
Parts to be injection moulded must be very carefully designed to facilitate the moulding process; the material used for the part, the desired shape and features of the part, the material of the mould, and the properties of the moulding machine must all be taken into account. The versatility of injection moulding is facilitated by this breadth of design considerations and possibilities.