SOLIDIFICATION SENSING FOR CLOSED-LOOP CONTROL OF INJECTION-MOLDING HOLD TIME

Hold time for injection molding is currently controlled open loop, usi ng a fixed time delay set by the machine operator. Insufficient hold t ime leads to inconsistent moldings, while excessive hold time increase s the cost of the part. We have developed new sensors that monitor the solidification of polymer in the mold. A closed loop strategy is demo nstrated where the hold time is automatically controlled based on feed back from a solidification sensor. Using this strategy, the hold time is set once in reference to the sensor signal, providing the minimum p roper hold time for each part under changing processing conditions. (C ) 1996 John Wiley & Sons, Inc.