Gas assisted moulding injects nitrogen into the melt while the cavity is partially filled, so the gas takes the path of least resistance through the thickest sections and hollows them out from the inside, pushing the melt outward to complete the fill. That solves the thick section problem directly rather than designing around it.
What the gas is doing
Plastic is injected to a partial shot, then nitrogen at pressure is introduced through the nozzle or through pins in the tool. Because gas follows the path of least resistance, it channels along thick ribs and bosses, hollowing them. It then holds pressure from inside during cooling, packing the part out uniformly without needing enormous injection pressure from the gate.
What it buys
Thick sections without sink marks, which is transformative on structural ribs and handles. Lower clamp tonnage, because holding pressure comes from the gas rather than from the machine, so a bigger part fits a smaller press. Less warp and lower moulded in stress. Shorter cycles on thick parts, since less material has to cool. And material saved in the hollow sections.
What it costs
A gas unit and controls, gas pins and channels in the tool, and process development that is genuinely more involved than conventional moulding. The gas channel must be designed deliberately so the gas goes where it is wanted, and a channel that lets gas break through into a thin section ruins the part. It is a specialist capability rather than a setting.
Where it is used
Large panels with structural ribs, handles and grips, automotive trim, furniture components and television and appliance housings. Anywhere a part needs a thick stiff section and a cosmetic surface on the other side of it, which conventional moulding makes a choice between and gas assist does not.
Questions people ask about gas assisted injection molding
What is gas assisted injection moulding?
Injecting nitrogen into a partially filled cavity so it hollows the thickest sections from the inside and packs the part out from within during cooling.
What problem does it solve?
Sink marks and warp over thick sections, and the clamp tonnage needed for large parts, since holding pressure comes from the gas rather than the machine.
Does it need special tooling?
Yes. Gas pins or a gas nozzle and deliberately designed gas channels, plus process development. It is a specialist capability, not a machine setting.
What are the risks?
Gas breaking through into a thin section and ruining the part, and inconsistent channel formation. Both are controlled by designing the gas channel deliberately.