Gas assisted injection molding combining internal and external gas pressures

摘要

A gas assisted injection molding system and method in which quantity of an inert gas is applied both internally and externally to a thermoplastic material introduced into an injection mold cavity during formation of an injection molded part. The system includes first and second mold portions defining a mold cavity. An injection means injects a quantity of a thermoplastic material into the mold cavity to form an injection molded part within the cavity. At least one internal gas inlet is provided for introducing a first quantity of gas into a portion the thermoplastic material to form a gas channel therein. The gas within the gas channel presses the thermoplastic material against a mold parting line defined by the intersection of the mold portions and forms a seal between the mold cavity and the mold parting line. As least one external gas inlet is located within one of the mold portions for introducing a second quantity of pressurized gas into the cavity to hold the thermoplastic material firmly against an inner surface of one of the mold portions. The system and method of the present invention thereby forms an injection molded part having a sink-free appearance side with a Class A finish.