Visualization and simulation of filling process of simultaneous co-injection molding based on level set method

Co-injection molding (CIM) is an advanced technology which was developed to meet quality requirements and to reduce the material cost. Theoretical investigations concerning it are very limited, especially for simultaneous CIM. The interactions of air, skin and core polymer melt in the process are very complex, which makes it more challenging to simulate free surface flows in the mold. Thus, this article presents a mathematical model for it. The extended Pom-Pom (XPP) model is selected to predict the viscoelastic behavior of polymer melt. The free surface is captured by the level set method. The article vividly shows the simultaneous CIM process by means of a visual numerical simulation technique. Both two-dimensional (2D) and 3D examples are presented to validate the model and illustrate its capabilities. The 3D flow behaviors of simultaneous CIM process are hard to predict numerically. To our knowledge, this is the first attempt at simulating melt flow behaviors in 3D simultaneous CIM based on the XPP constitutive equation and visual technique. The numerical results are in good agreement with the available experiment results, which establish the capability of the multiphase flow model presented in this article to simulate the flow behaviors of polymer melt in simultaneous CIM process.

Numerical Simulation of the Effect of Processing Parameters on the Flow Behavior and Break-through Phenomenon in Co-Injection Molding

In this work, a three-dimensional finite element flow analysis code is used to study the flow behavior during sequential co-injection molding. Non-Newtonian, non-isothermal flow solutions 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. Solutions are presented for the filling of a spiral-flow mould for which experimental measurements are available. The numerical approach is shown to predict 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 and the numerical solution is in good agreement with the experiment. Those phenomena are hard to predict numerically and to our knowledge this is the first attempt at simulating the three-dimensional melt behavior during core expansion and core breakthrough. The predicted flow front behavior is compared to the experimental observations for various skin/core melt temperature, skin/core viscosity ratio, and core injection delay. Simulation results are in good agreement with experimental data and indicate correctly the trends in solution change when processing parameters are changing.