Abstract: The present cavity filling model of water-assisted injection molding is suitable to thin-walled modeling but does not work with large diameter parts. Besides, the model doesn’t consider turbulence in field of water with high Re number, fountain flow at melt front and wall thickness forming naturally. The simulation model of cavity filling process in water-assisted injection molding is based on the time dependent analysis, turbulence models, viscoplastic constitutive equations and so on. The k - ε and k - ω model are compared and the interfacial instabilities in multiphase-multilayer are analyzed. The simulation on various process control parameters is discussed. The investigation shows that increasing melt temperature and water injection flow rate or shortening delay time makes the residual wall thickness decrease. Extending delay time or decreasing melt temperature or increasing water injection flow rate makes the water injection pressure increase. These research results are close to experimental findings by other investigators. Especially, the delay time has little effect on load pressure but the effects of water injection flow rate and delay time are substantial. And the coupling characteristics of water injection pressure and flow rate are obvious. Hence the optimization of pressure control of water hydraulic system for water-assisted injection molding oriented by molding effects is provided. This is an important method to develop water-assisted injection molding technique.

Key words: Cavity filling process, Hollow molding ratio, Multiphase-multilayer flow, VOF model, Water-assisted injection molding