Gas-assisted injection (modeling) molding, also known as gas injection (shot molding) molding, is a new injection molding process. It is one of the most important developments in the injection molding industry since the advent of reciprocating screw injection machines. Gas-assisted injection molding is an extension of injection molding. It is developed on the basis of injection molding technology and structural foam injection molding. It can also be considered as a certain compounding of injection molding and hollow molding. In this sense, it can also be called "Hollow injection molding". The principle is to replace the resin in the cavity with a relatively low pressure gas during the pressure holding stage of the original injection molding. Gas-assisted injection molding can be realized by adding a gas supply device to the existing injection molding machine. The gas supply device is composed of an air pump, a high pressure gas generating device, a gas control device, and a gas nozzle. The gas control unit is continuously supplied with a special compressor, and is controlled by an electric control valve to keep the pressure constant. The pressure usually has 3 levels. A gas control unit can be equipped with multiple injection molding machines.
The gas generally used is nitrogen. Gas pressure and gas purity are determined by the shape of the molding material and the shape of the article. The pressure is generally 5~32MPa and the highest is 40MPa. The high pressure gas is injected from the gas nozzle at a set pressure timing in each injection. One or more gas nozzles are provided on the injection molding machine nozzle, the flow path or cavity of the mold.