Numerical Simulation Investigation on Interfacial Penetration Mechanisms in Liquid Carbon Dioxide‐Powered Projectile‐Assisted Injection Molding

Liquid carbon dioxide‐powered projectile‐assisted injection molding (LCO 2 ‐PAIM) uses a medium fluid with dual gas–liquid characteristics, enabling high‐precision forming of hollow pipes. Numerical simulations compare LCO 2 ‐PAIM with gas‐powered projectile‐assisted injection molding (G‐PAIM) and water‐powered projectile‐assisted injection molding (W‐PAIM), revealing the role of LCO 2 during interfacial penetration of the projectile. Results show that only the LCO 2 directly in contact with the melt undergoes phase change; the bulk fluid remains liquid. Interfacial penetration induces a sharp pressure rise and nonlinear velocity growth. The thermophysical properties of the medium fluid govern melt flow behavior during projectile advancement. The residual wall thickness uniformity of LCO 2 ‐PAIM lies between those of W‐PAIM and G‐PAIM. Notably, the choice of fluid has negligible influence on the average wall thickness, yet it is the dominant factor controlling thickness uniformity. These results verify that LCO₂ is an appropriate alternative medium for balanced geometrical precision control of hollow pipes.