Numerical Simulation of the Flow Behavior and Breakthrough Phenomenon in Co-Injection Molding

Abstract

A study of the flow behavior during sequential co‐injection molding is shown using a three‐dimensional finite element flow analysis code. Solutions of the non‐Newtonian, non‐isothermal melt flow are obtained by solving the momentum, continuity and energy equations. Two additional transport equations are solved for tracking polymer/air and skin/core polymers interfaces. The co‐injection model is integrated into the NRC’s 3D injection molding software. Solutions are shown for the filling of a spiral‐flow mould for which experimental measurements are available. The numerical approach predicts the core advance stage during which the core flow front catches up on the skin flow front and the core expansion phase when the flow fronts of core and skin materials advance together without breakthrough. The breakthrough phenomenon is also predicted. The predicted flow front behavior is compared to the experimental observations for various skin/core melt temperature and skin/core viscosity ratio. Simulation results are in good agreement with experimental data and indicate correctly the trends in solution change when processing parameters are changing.