The process capability of multi-cavity pressure control for the injection molding process

Cavity pressure has been recognized as a critical process parameter for the injection molding of high quality thermoplastic parts. This interest has led to the achievement of closed loop cavity pressure control, but only at one point in the mold cavity. A system has been recently described that extends this capability to provide simultaneous control of cavity pressure at multiple locations in the mold through the addition of dynamic valves In the-melt delivery system, each of which can be independently controlled to meter flow and pressure to its portion of the mold, This paper describes the ability of the multi-cavity pressure control system to improve process capability and molded part quality. Experimental investigation has shown that the technology enables significant process flexibility to arbitrarily balance flow, move knit-lines, and control multiple part dimensions. in the presence of typical production process disturbances, moreover, closed loop multi-cavity pressure control was shown to increase the process capability index, Cp, from 0.52 for the conventional injection molding process to 1.5. After these capabilities have been discussed, several limitations of the process are described that lead to promising areas of future research.