A Dynamic Injection-Molding Process Model for Simulating Mold Cavity Pressure Patterns

The quality of injection-molded parts is typically controlled in the plant using statistical techniques that involve measuring parts as well as monitoring processing parameters. Part quality is also controlled by machine operators who adjust processing conditions in response to trends in process behavior. To achieve direct on-line monitoring and automatic control of part quality, a multivariable, nonlinear process model must be developed that relates process behavior to machine-controllable parameters. Presented in this work are the details of such a model derived from first principles and proven correlations. Because recent work has shown that complete mold cavity pressure patterns are good indicators of part quality, the focus of this lumped-parameter model is to simulate mold cavity pressure patterns observed during the filling, packing, and cooling stages of the process, given machine set points for barrel temperature and holding pressure. The model is validated experimentally using a production injection-molding machine and parameter-sensitivity case studies are presented.