Method of precision volumetric control of a moldable material in an

Abstract

A method of operating an injection molding machine having a pair of separable mold elements forming a mold cavity therebetween with means for opening and closing the mold elements with means for introducing a moldable material into the mold cavity at a first pressure and for exerting a second pressure on the moldable material as it cures in the cavity. The method controls the molded product and comprises the steps of closing the mold elements and introducing a moldable material into the mold cavity. The separation of the mold elements is measured during the injection of the moldable material and a predetermined separation of the mold elements is detected. Upon detecting the predetermined separation the pressure is changed from the first pressure to the second pressure and the separation of the mold elements is continued. Measurement of mold element separation is continued and the cessation of the increase in the separation of the mold elements is detected. A determination is made whether or not the cessation occurs within a predetermined separation window. If the cessation is not within the window a signal is generated to indicate that the cycle has exceeded the product limit. If the cessation is within the window then the cycle is continued and the second pressure is maintained until the moldable material has cured. The mold is then opened.