3D numerical study of race-tracking and air entrapment phenomena in polymer filling process

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The race-tracking effect and air entrapment are two important phenomena that restrict the quality and performance of injection molded parts. This study considers two types of parts with different wall-thickness distributions. Through numerical simulations combined with experimental observations, the race-tracking effect and air entrapment phenomena during polymer melt filling in 3D cavities are investigated, with particular emphasis on the influence of the thin-to-thick wall-thickness ratio. A two-phase flow model is developed by coupling the Navier–Stokes equations with the level set equation, and is discretized using a collocated grid finite volume method and the SIMPLE algorithm is employed for pressure–velocity coupling. The results show that the proposed model can accurately predict melt front evolution in complex cavities and effectively capture the race-tracking effect and air entrapment phenomena during filling. Furthermore, the thin-to-thick wall-thickness ratio plays a crucial role in both phenomena: decreasing this ratio intensifies the race-tracking effect, and for circular cavities, also increases the trapped air area.