ABSTRACT
Process control is recognized as an important means of improving the performance and consistency of thermoplastic parts. This chapter provides an overview of modeling, measurement, and control strategies in polymer processing, and discusses some of the difficulties posed by their complex and distributed nature. Control of injection molding is significantly challenged by the nonlinear behavior of the polymeric materials, dynamic and coupled process physics, and convoluted interactions between the mold geometry and final product quality attributes. Process variability in injection molding further complicates process control. The sources of variability are attributed to the thermoplastic resin, the injection molding machine, and environmental factors. Prior to the 1970s, the majority of molding machines utilized open-loop control for most subsystems. Further advancements in state-variable control are becoming possible through development of remote smart sensors. The predominant practice for set-point specification in large job operations is to develop an empirical model based on data obtained from a set of designed experiments.
