Injection moulding is used to make a wide range of plastic products, from enclosures to model construction kits, chairs and toys. The process is very fast and complicated shapes can be made from both thermoplastic and thermosetting polymers.

There are also a number of different types of injection moulding techniques and each is suited to a different application.  In this two-part post we look at six different types of moulding techniques.

Reaction injection moulding

Unlike injection moulding, Reaction injection moulding (RIM) techniques utilise low-viscosity liquid polymers in thermoset – not thermoplastic – processes. Through a variety of chemical reactions, these polymers expand, thicken and harden only after they’re injected into the heated mould, accommodating much more intricate designs than ordinary moulding. Raw materials and moulding techniques can be selected and even customised to precisely deliver desired weight, strength, density and hardness characteristics. The result is large polyurethane parts with much lighter weight than those created by more commonplace processes.

Liquid injection moulding

Liquid moulding differs from the standard RIM process in that it relies on mechanical mixing rather than pressurised impingement mixing, and it focuses specifically on liquid silicone rubber and similar elastomeric materials. It is capable of efficiently producing a large number of versatile items, including seals, o-rings, isolators, and electronic contacts. A large part of liquid injection moulding’s versatility derives from the material properties of liquid silicone materials. These silicones exhibit a high degree of heat and flame resistance, tensile strength, and flexibility.

Gas assist injection moulding

Gas assist injection moulding is a low-pressure process utilising nitrogen gas to apply uniform pressure throughout the moulded plastic part. By displacing molten plastic from thicker sections of the part toward areas in the cavity that are last to fill, nitrogen gas pressure creates channels within the part. Through the gas channels, pressure is transmitted evenly across the part, eliminating warpage, sink marks and internal stress. As a result, reductions in clamp tonnage, cycle time, and part weight are realised while the strength and rigidity of the part is increased.

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