Numerical Simulation Of Penetration Behavior In Water-assisted Injection Molding

Water-assisted injection molding technology is the new molding methods of production of hollow or partially hollow products. The process has the advantage of shorter cycle time, thinner and more uniform wall thickness of workpiece etc., have good development prospects.In water-assisted injection molding process, injection volume, temperature, pressure, flow rate, the penetration of water in the melt and the water pressure of time and so directly affect the cooling and crystallization of polymer melt and the material distribution and products performance, how to reasonably determine and control of these factors for the water assisted injection molding critical success, this is the current application and promotion of the technology needed to solve urgent problems. To do this, the water-assisted injection molding technology based on the numerical theory of the traditional injection molding, gas-assisted injection molding for in-depth study in order to quickly achieve low power consumption to the water-assisted injection molding process optimization.Based on rheology in polymer processing and mechanics of fluids, for water-assisted injection molding process characteristics, after reasonable simplifying and assumptions, the establishment of a water-assisted injection molding process is described in the mathematical model. The dimensionless approach and a perturbation method is applied to derive the water penetrate length of the residual wall thickness and capillary number Ca and the relationship between. Then, based on these results, the governing equations for viscous compressible non-Newtonian polymer melt in the second penetration of Water-Assisted Injection Molding (WAIM) were constructed using dimensionless method. To get the numerical solution, the varational equation for pressure was derived with integration by parts. The formula for velocity expressed by pressure gradient was also derived by the same method. In order to simulate water advancing distance along the radial direction during the second penetration, a formula for interface velocity depending on water pressure, melt density, viscosity, penetrated length and penetrated radius was generalized using integration by parts and mechanical principle. Finally, a program was developed to get the numerical solution for pressure, temperature, velocity and residual thickness during WAIM. Our results show that when the water injection pressure amplified, residual wall thickness, no significant effect on the penetration length; when melt temperature rose, the residual wall thickness decreases, the penetration length has no significant impact. Meanwhile, the experimental results show that the simulation of water-assisted injection molding,only used first penetration theory is not enough, also need to use the second penetration theory and algorithm.