Model and simulation of water penetration in water-assisted injection molding

Water penetration behavior in the polymer melt is an important part of water-assisted injection molding (WAIM) technology. Based on the traditional injection molding model, an improved WAIM mathematical model was proposed, in which shear stress transportation kappa-omega turbulent model was used to reflect the turbulent characteristics of water and predict the cooling of the melt by the water. In addition, the free interface of water/melt two-phase flow was tracked by volume of fluid, and the distribution of temperature, velocity, and pressure were calculated by computational fluid dynamics method. The results showed that in the long straight water channel, water penetration was uniform and smooth, and wall thickness difference is small. However, it was easy to produce water fingering in variable cross-section and L-shaped water channels. The fingering could effectively be reduced by the smooth transition of size and fillet. Reasonable fillet radius made the distribution of residual wall thickness of the inner and outer relatively uniform, but the wall thickness difference was inevitable. The fast cooling of the melt by the water was verified, so the cycle time could be shortened effectively.