Numerical simulation links wall-thickness ratio to race-tracking and air entrapment during polymer filling

A numerical and experimental study reports that the thin-to-thick wall-thickness ratio influences two phenomena during polymer melt filling: race-tracking and air entrapment. In the simulations, reducing the ratio intensified race-tracking, while for circular cavities it also increased the area of trapped air.

The researchers investigated two types of parts with different wall-thickness distributions. They developed a three-dimensional, two-phase flow model that coupled the Navier–Stokes equations with the level set equation. The model used a collocated-grid finite-volume discretization, with the SIMPLE algorithm handling pressure–velocity coupling.

According to the published abstract, the model accurately predicted the evolution of the melt front in complex cavities and captured race-tracking and air entrapment during filling. The results also indicate that wall-thickness distribution is an important factor in both effects, with the response of trapped-air area differing by cavity geometry: the increase associated with a decreasing thin-to-thick ratio was reported for circular cavities.

This is a study of polymer filling processes based on numerical simulation combined with experimental observations, rather than a clinical or biological investigation. The reported evidence concerns two part geometries and focuses specifically on the influence of the thin-to-thick wall-thickness ratio. Because only the abstract and article summary were available for this report, details of the experimental protocol, quantitative uncertainty, validation measurements, and the range of geometries and ratios examined cannot be assessed. The source also identifies the publication as an early-access version of accepted peer-reviewed research that may undergo further editing.

Subject of Research: Numerical modeling of race-tracking and air entrapment during polymer filling

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

Article References: Liu, Y., Liu, Q., & Jiang, C. (2026). 3D numerical study of race-tracking and air entrapment phenomena in polymer filling process. Scientific Reports. https://doi.org/10.1038/s41598-026-74878-6

Image Credits: AI Generated

DOI: 10.1038/s41598-026-74878-6

Keywords: polymer filling, injection molding, race-tracking, air entrapment, two-phase flow, numerical simulation, melt-front evolution, wall-thickness ratio, circular cavities, numerical, entrapment, phenomena