Two‐Phase Flow Simulations for Injection Molding Applications: Comparison between COMSOL Multiphysics and XNS In‐House Solver

ABSTRACT Injection molding is a manufacturing process for plastic components where precise geometries and part properties, such as local strength and stiffness, are critical. The mold filling phase, during which the hot molten polymer is rapidly injected into the cooled mold cavity, presents significant simulation challenges due to steep temperature and velocity gradients, as well as the nonlinear visco‐elastic behavior of polymers. In this work, we present a comparative study using a widely known commercial simulation tool, COMSOL Multiphysics, and our in‐house‐developed solver, XNS, with a specific focus on the treatment and impact of wall boundary conditions. For the comparison, we use a 2D macroscale test case. For both solvers, stabilized linear finite elements are used, and they utilize a two‐phase flow formulation, with the level‐set method to capture the interface. The two solvers differ in their definition of the level set function and in their variable Navier‐slip algorithms as boundary condition. The results indicate that variations in the treatment of wall boundary conditions lead to differences in both the advancing profile of the interface and the width of the frozen layer. This study highlights the critical role of accurately modeling wall boundary conditions in predicting the onset of solidification and subsequent part quality. Moreover, our findings demonstrate that the in‐house solver achieves accuracy comparable to that of COMSOL Multiphysics with a drastically reduced computational time, while offering more flexibility for the wall boundary conditions and the potential for a more physical representation of them.