CAVITY PRESSURE CONTROL DURING THE COOLING STAGE IN THERMOPLASTIC INJECTION-MOLDING

The evolution of cavity pressure during the injection molding cycle ha s a strong influence on the quality of the molded part. The injection molding cycle can be divided into three stages: filling, packing, and cooling. In a previous paper, the authors reported on the design and i mplementation of a strategy to control cavity pressure during filling and packing. This paper deals with cavity pressure control during the cooling phase. A coolant temperature control system has been designed for the control of cavity pressure during the cooling phase. Alternati ve variables have been defined to describe changes in cavity pressure during the cooling phase. The concept of controlled pressure cooling t ime (CPCT) has been defined and selected as the most appropriate contr olled variable. The dynamics of CPCT have been studied in relation to coolant temperature. A control system for CPCT has been designed and i mplemented. Finally, the paper shows that the control of CPCT is an ef fective approach for the control of cavity pressure during cooling.