METHOD AND APPARATUS FOR GAS ASSISTED INJECTION MOLDING HAVING PRECISE CONTROL OF INJECTION AND HOLDING PRESSURE WITH STEPPED HOLDING PRESSURE CAPABILITY

摘要

A method and apparatus for gas assisted injection molding which will first inject a shot of molten plastic into a suitable mold, shut off the plastic flow into the mold, and either immediately, or after a delayed time, inject a suitable pressurized gas into the mold at a desired injection pressure. The pressure of the gas in the mold is then controlled by stepping up or stepping down the pressure in the mold in a series of steps to arrive at a second predetermined and precisely controlled pressure. The predetermined pressure is held for a desired time. The setting and holding of pressure is repeated as many times as desired, and is then stepped down to a final pressure. The mold is then opened, and the article is removed.