Multi-cavity pressure control in the filling and packing stages of the injection molding process

Cavity pressure has been recognized as a critical process parameter for the injection molding of high quality plastic parts. Recent developments in injection molding process technology have enabled closed loop control of cavity pressure at one point in the mold. In this paper, a scheme is described that enables the simultaneous control of cavity pressure at multiple locations in both multi-gated parts and/or multi-cavity molds. This has been achieved by the addition of dynamic valves in the melt delivery system, each of which can be independently controlled to meter the flow and pressure of the polymeric melt to its portion of the mold. The development and capabilities of the control system are presented, demonstrating the feasibility of simultaneous multi-cavity pressure control in both the filling and packing stages of the injection molding process. A description of the ability of multi-cavity pressure control to improve process capability and molded part quality is presented in a companion paper.