Process control strategies for injection molding processes with changing raw material viscosity

Abstract

Abstract The ultimate goal of process control in injection molding is to achieve a reproducible part quality despite changing boundary conditions and disturbances. Especially, changing material viscosities have a considerable impact on part quality and are often inevitable. This study starts with a brief review of the state of the art in injection molding control strategies with regards to melt viscosity. The requirement for a process control strategy with a direct feedback to part quality adapting to the current process viscosity and using in-mold data is derived. In this paper, a fuzzy controller using a pressure loss measurement is implemented for a cycle-to-cycle control of injection velocity based on the current melt viscosity. Depending on the conditions, the controller enables to realize a set point jump in viscosity after approximately six injection molding cycles. To improve control performance and to realize an online closed-loop control in the injection phase, the system behavior of a mold using pressure sensors in the hot runner manifold to obtain a viscosity equivalent indicator is analyzed. The mold in combination with a fuzzy controller using injection velocity and hot runner temperature as actuating variables provide a sound basis for viscosity control in injection molding.