9 Control of Polymer Processing David Kazmer University of Massachusetts, Amherst Introduction Process Description Process Variability Modeling Process Control Machine Control • State-Variable Control • Set-Point Control Kourosh Danai University of Massachusetts, Amherst Conclusions Introduction Process control is recognized as an important means of improving the performance and consistency of thermoplastic parts. However, no single control strategy or system design is universally accepted, and manufacturing systems continue to produce defective components during production. 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. Most plastic parts are. | 9 Control of Polymer Processing David Kazmer University of Massachusetts Amherst Kourosh Danai University of Massachusetts Amherst Introduction Process Description Process Variability Modeling Process Control Machine Control State-Variable Control Set-Point Control Conclusions Introduction Process control is recognized as an important means of improving the performance and consistency of thermoplastic parts. However no single control strategy or system design is universally accepted and manufacturing systems continue to produce defective components during production. 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. Most plastic parts are fabricated by thermoforming extrusion or injection molding. In thermoforming and its variants vacuum forming blow molding male forming drape forming plug-assist forming etc. a continuous sheet of material is heated first until it becomes pliable elastic modulus of approximately Mpa and then it is expanded at strain rates of approximately 100 per second to assume the shape of an evacuated mold. The hot sheet is then cooled by conduction of heat to the mold which itself is cooled with conditioned recirculated water. The resulting part typically exhibits thickness distributions from 10 to 90 of the initial sheet thickness with mold cycle times varying from 15 seconds to 5 minutes per part. Unlike thermoforming which is a cyclic process extrusion is a continuous and steady-state process. In extrusion solid thermoplastic pellets are fed into a rotating screw to be compacted into a tightly packed solid bed. The thermal energy for melting comes from the mechanical power of the motor that is consumed to rotate the screw. The tapered flight on the screw geometry is designed to match the rate of dissipative melting to present minimum flow restriction and smooth flow. The .
