Abstract
Steps towards process control of the complex, multi-variable injection moulding process are presented. In-process measurements, in particular melt and hydraulic pressures in the primary injection stage, are shown to provide a sensitive means of monitoring changes in the process and changes in the polymer feedstock. Correlations have been observed between real time process measurements, in the form of specific time integrals of melt and hydraulic pressure, and product quality measures, such as product weight or dimensions. The research has been validated in both scientific laboratory and factory studies, and for a range of polymers, injection moulding technologies and complexities of product. Such correlations, and the specific integrals upon which they are based, can therefore form the basis of meaningful statistical process control for injection moulding or a viable closed-loop control strategy.
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