Physically Based Bubble Growth Model for Micro-Scale Foam Injection Moulding CFD Simulation

Predicting spatially varying cell morphology in foam injection molding is required for microstructure-based part design but remains limited by spherical bubble-growth models. This study extends a compressible, viscoelastic volume-of-fluid framework with a diffusion-controlled bubble-growth model. Bubble-specific mass-transfer rates are calculated from geometry, temperature-dependent gas properties, interfacial concentration, and prescribed bulk gas concentration, and introduced iteratively as local mass sources in OpenFOAM. The model was evaluated for two polycarbonate-nitrogen parameter sets and two plate positions against experimental cross-sections. The approach produced continuous and monotonic bubble growth. The simulations reproduced through-thickness trends, including larger cells in the core, decreasing cell size toward the walls, and preferential deformation in the shear layers. The simulated trends in cell density and area agreed qualitatively with the experiments, and aspect ratios of 1.5-2.0 for one parameter set were comparable to measurements. Absolute morphology descriptors were not reproduced quantitatively because of the two-dimensional representation, simplified nucleation history, prescribed bulk gas concentration, and one-way coupling. The deformation results rely on a case-specific reduction to 10% of the macro-scale pressure difference. The model provides a physically motivated methodological framework for resolving bubble growth and qualitative spatial trends in foam morphology.