Filling-To-Packing Switchover Mode Based on Cavity Temperature for Injection Molding

Abstract

A filling-to-packing switchover mode based on cavity temperature was presented and compared with three other switchover modes. The part weight and dimension served as the main measure to probe the process capabilities. It revealed that the switchover mode based on cavity temperature yielded better part quality, more consistent part weight and dimension. The switchover temperature and sensor position should be considered for achieving such high process capabilities. The switchover mode based on cavity temperature can be used to accommodate the product weight change due to the variation of mold temperature, which is something that the other switchover modes cannot handle. INTRODUCTIONDuring injection molding, the position at which the machine switches from filling phase to packing phase is referred to as the switchover point. Plastic processors have noted for years that the repeatability of molded part qualities is significantly affected by the ability to identify the proper switchover point. Two inadequate filling-to-packing switchover conditions are: switchover occurring too early and switchover occurring too late. If the switchover takes place prematurely, it may lead to insufficient packing, the injection part can be easily rejected due to reduced dimensions, being underweight, or showing sink marks. The switchover occurring too late will cause an over-packed cavity, the molding will flash or may stick in the mold. Over-packing further adds weight and stress to the part, and makes de-molding more difficult.There are many filling-to-packing switchover modes that machines are capable of using today. The more common

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