Gas-assisted injection molding is a low-pressure process utilizing nitrogen gas to apply uniform pressure throughout the molded 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 warping, sink marks, and internal stress. As a result, reductions in clamp tonnage, cycle time, and part weight are realized, while the strength and rigidity of the part is increased.
Gas-assisting allows molders the freedom to design plastic parts without restrictions and limitation inherent to conventional plastic injection molding.
The chief difference between water and gas is that water is not compressible. When injected into the melt, the leading edge of the water forms a solid boundary, or highly viscous membrane. This membrane forces molten material forward instead of the polymer forcing the water to the side. The primary reason for this action is the higher viscosity and incompressibility of water compared with gas. This viscous front acts as a ram that cores out the part. The front also cools the melted plastic as it is pushed down the mold cavity by the water pressure.