Get High-Gloss Parts with Reinforced Polyester Resin and Gas-Assisted Injection Molding

Need a high-gloss plastic part? If your part is rod-shaped or large and flat with structural ribs, or if it’s a complex mix of thick and thin walls, don’t discount weight-saving gas-assist injection molding.

Gas-assist injection molding (GAIM) is a method of pressurizing an injection-molded part with gas to provide extra packing force. The gas forms a hollow cavity inside the part via a network of flow channels or by direct injection. GAIM’s advantages include the ability to cut part weight and material cost, the ease of combining parts with different wall thicknesses into a single design, and the reduced press capacity needed to produce fully consolidated parts.

Until recently, engineers avoided the technique for parts that needed high-gloss surfaces. Now molding vendors combine tooling, process controls, and materials that produce strong, high-gloss parts that are lighter and more economical than those from traditional injection molding.

Gas-assist process
GAIM starts when the mold closes and an injection nozzle shoots a precise quantity of molten resin into the mold. Although the resin does not completely fill the cavity, the screw feeding the nozzle bottoms out before returning to its initial position.

After a preset delay, the system injects pressurized inert gas — usually nitrogen with 99% or greater purity — into the melt. The system holds the gas pressure in the part for the entire packing and cooling phases, and then vents the gas before the mold opens for part removal.