What is Gas-Assisted injection Mould

Gas assisted injection Mould is a molding process where an inert gas is injected into the melted plastic pushing it further into the mold and resulting in hollow parts.

In the gas assist molding process, the plastic material is melted and injected into the mold cavities via the conventional plastic injection molding process. Plastic material in contact with the mold walls begins to solidify first. As this happens, nitrogen gas is injected into the mold through strategically designed and placed gas channels, providing pressure that pushes the plastic material into the mold extremities. Once the plastic cures, the nitrogen is vented and the gas assist injection molded plastic parts are removed from the mold.

The primary advantage of gas assist is cost reduction by improving productivity. Using lower clamp tonnage means using a smaller machine thus improving the quoting process, not to mention the eliminating the cost of a larger machine. Cycle time reductions save costs as you do not need pack and hold times and pressures. This of course saves time. In gas assist you never completely fill the part. By using a short shot process there is less plastic injected and less plastic to cool. The gas will also promote cooling which slashes cycle time. New methods of tool design flow and fill is improved again saving time. In very thick parts, gas follows the path of least resistance which promotes low pressure fill without packing out the outward features of the pat. This means reductions in part weight; even thin walled applications. Thick walled parts can have up to seventy percent less part weight. While using less plastic may weaken the part it actually forms a tube configuration with less stress which actually improves strength. You also have to remember that by eliminating resin especially engineering grades, is quite cost effective. This of course depends on the end use of the part.

Gas-assisted injection molding to provide an internal hollow shape (Green and blue colors indicate inert gas and polymer melt respectively)

• Contact an expert when considering gas assist injection molding.
• Control of the short shot is critical. Make sure the barrel and screw tolerances are within specifications.
• Use a highly controllable gas system.
• Gas assist is not always the correct process.
• There will always be a hole in the part.
• Using a mold flow simulation will be very valuable before deciding about gas assist.