A novel method for determining the pressure dependent characteristics of polymer melt during micro injection molding

Micro injection molding is used to manufacture thin-walled parts with micron-scale structures. wherein high shear rate and high injection pressure process conditions appear. Consequently, the pressure dependence of polymer melt viscosity at the microscale cannot be ignored. However, in the simulation analysis of the microinjection molding process, almost all the Cross-WLF models of polymeric materials are omitting the pressure dependence parameter D₃. This has a huge impact on the accuracy of the simulation results. Herein, a method that combines experimental characterization and filling simulation is proposed for the determination of the pressure dependence of polymer melts during micro injection molding. D₃ in the Cross-WLF model of Polymethyl methacrylate (PMMA) and Cycloolefin copolymer (COC) is characterized by capillary rheometer and counter pressure chamber. The developed viscosity model including D₃ is used for a filling simulation and is compared with the experimental results. The model flow simulation results showcases that the prediction accuracy of the viscosity model is significantly improved after considering D₃. These results are of great significance, as they can be used to reduce the development cost and to improve the simulation accuracy of the micro injection molding filling process.