Since the advent of reciprocating screw injection molding machine, gas-assisted injection molding is one of the most important developments of injection molding technology. It uses high-pressure gas to produce hollow cross-section in injection molding parts, which reduces residual internal stress of products, eliminates surface shrinkage marks of products and reduces materials, showing incomparable advantages of traditional injection molding. The process of gas-assisted injection mainly includes three stages: the initial stage is melt injection. At this stage, plastic melt is injected into the cavity, which is the same as traditional injection molding, but the melt only fills 60%-95% of the cavity, and the specific injection amount varies from product to product. The second stage is gas injection. At this stage, high-pressure inert gas is injected into the melt core, and the melt front continues to flow forward under the drive of gas pressure until the whole cavity is filled. In gas-assisted injection molding, the melt flow distance is obviously shortened and the melt injection pressure can be greatly reduced. Gas can enter the workpiece directly from the cavity from the main channel or through the gas injection element. Because gas always permeates in the direction with the lowest resistance (high temperature and low viscosity), it is necessary to specially design gas channels in the mold. The third stage is gas pressure maintaining. At this stage, the parts are cooled while maintaining the gas pressure. Further, the pressure transmission characteristics of gas are used to press the parts evenly outward, and the volume shrinkage (secondary infiltration) caused by melt cooling and solidification is supplemented by gas expansion to ensure that the outer surface of the product is close to the die wall.

Gas-assisted technology makes it possible to use injection molding for many parts that cannot be injected by traditional technology. It has been widely used in almost all fields of plastic parts such as automobiles, household appliances, furniture, electronic devices, daily necessities, office automation equipment, building materials, etc. As a challenging new technology, it opens up a new application field for plastic molding. Gas-assisted technology is particularly suitable for manufacturing injection molded products in the following aspects: