Plastic injection moulding makes plastic parts: a heated, molten thermoplastic is injected under high pressure into a steel or aluminium mould, cools, then the part is ejected. It is the reference process for producing plastic parts in high volumes, quickly and with great repeatability.
An injection moulding machine combines a plasticising unit (a screw in a heated barrel that melts and meters the material) and a clamping unit that keeps the mould closed. The mould has two half-cavities, runners and a gate, a cooling circuit and ejectors; slides form the undercuts. The cycle runs through closing, injection, holding (which compensates for the material’s shrinkage), cooling, opening and ejection: from a few seconds to a few tens of seconds. Common materials are PP, PE, ABS, polyamide (with or without glass fibre), POM, PC and thermoplastic elastomers. Design follows rules: even wall thicknesses, draft angles, fillets, ribs rather than thick walls, which cause sink marks. Shrinkage, from a few tenths of a per cent to a few per cent depending on the material, must be compensated for in the cavity.
Injection moulding is used for enclosures, covers, clips, connectors, caps, automotive parts and medical devices. The mould is a major investment, amortised over the run: the guide to the price of an injection mould details it. For prototypes or small runs, additive manufacturing, machining or vacuum casting are preferred. Choosing the material is the subject of the guide engineering plastics, and the plastics and moulding page presents the workshops.
In a quote request. Supply the 3D model (STEP file) and the drawing, the material and its colour, the expected annual and total quantity, the surface appearance (texture, polish) and the critical dimensions. State any special requirements (food contact, UV resistance, UL 94 fire rating), and agree on mould ownership, the number of cavities and its maintenance.