EXPANSION INJECTION MOLDING METHOD

摘要

PURPOSE:To make it possible to stably obtain a forming product having a smooth surface and reduced in the irregularity of quality, by starting the advance of an injection screw at the point of time when the pressure of the gas in a cavity reaches predetermined pressure and injecting and filling a molten resin before rapidly performing the venting of gas. CONSTITUTION:The pressure of the gas in a cavity is detected by a gas pressure detector 5 and, when said pressure reaches preset pressure, the injection screw 3 of an injection molding machine 1 advances by the signal to a hydraulic pressure controller 8 and the injection of a forming resin into the cavity is started. When the injection screw 3 reaches the position preset by a screw position detector 6 at the point of time when the pressure in the gas in the cavity filled with the molten resin reaches a definite value, a gas exhaust valve 9 is opened and the venting of gas is rapidly performed. By this rapid venting of the gas, the next expanding process becomes smooth and the generation of appearance inferiority is easily prevented.