Injection mouldings count for a significant proportion of all plastics products from micro parts to large components such as bumpers and wheelie bins. Virtually all sectors of manufacturing use injection moulded parts - the flexibility in size and shape possible through use of this process have consistently extended the boundaries of design in plastics and enabled significant replacement of traditional materials thanks to light weighting and design freedom. The list below shows the type of products that can be injection moulded, but is by no means comprehensive: Acrylonitrile-Butadiene-Styrene ABS, Nylon PA, Polycarbonate PC, Polypropylene PP, Polystyrene PS. The essential elements are as follows:
Material is introduced into the injection moulding machine via a Hopper. The injection moulding machine consists of a heated barrel equipped with a reciprocating screw (driven by a hydraulic or electric motor), which feeds the molten polymer into a temperature controlled split mould via a channel system of gates and runners.
The screw melts (plasticises) the polymer, and also acts as a ram during the injection phase. The screw action also provides additional heating by virtue of the shearing action on the polymer granules rubing against each other.
The molten polymer is injected into a mould tool that defines the shape of the moulded part.
The pressure of injection is high, dependant on the material being processed; it can be up to one hundred bar. Mould tools tend to be manufactured from steels, (which can be hardened and plated), and Aluminium alloys for increased cutting and hand polishing speeds. The costs associated with tool manufacture means that injection moulding tends to lend itself to high volume manufacture.
The tool can be used to manufacture one consistent part in a repeating process or incorporate multiple cavities (a multi impression tool), that means many components can be manufactured on the same tool repeatedly with a single injection.
