Gas assisted injection moulding

Process:   In the first instance molten plastics material is injected into a mould (see injection moulding).  Gas is then injected into the material pushing it to the extremes of the mould leaving a hollow product. 

Introduced:   In the 1970s, American inventor James Watson Hendry, developed the first gas-assisted injection moulding process, which permitted the production of complex, hollow articles that cooled quickly. This improved design flexibility as well as the strength and finish of manufactured parts while reducing production time, cost, weight and waste.  However, it was not until the 1990s that the process has been widely used commercially. 

Plastics:   Most thermoplastics including polypropylene, acrylonitrile butadiene styrene, high impact polystyrene, polycarbonate, and polyamide (including glass filled grades).  

Marks:   Similar to injection moulding although external gas assisted injection moulding minimises ejector marks as ejector pins are not required and internal gas assist can also leave a “shadow” mark on the part at the point of gas injection, where the gas pressure is highest. 

Tooling cost:   High 

Production volume:   High 

Uses:   Tube-and rod-like parts, such as clothes hangers, grab handles, chair armrests, shower heads, and water faucet spouts.  Large, sheet-like, structural parts including automotive panels, business machine housings, outdoor furniture, and satellite dishes.  Complex parts consisting of both thin and thick sections, such as television cabinets, computer printer housing bezels, and automotive parts.