Research On Gas Assisted Injection Molding Filling Simulation Based On Surface Model

A practical model of cavity filling in gas assisted injection molding (GAIM) based on the surface mode has been presented on the basis of filling simulation of conventional injection molding, which avoids the fussy second modeling in filling simulation based on the mid-plane mode and the huge amount of calculation time in fully 3D simulation.This paper introduces circular intersection approximation for the gas channel considering that the cross section of gas core in the gas channel after gas penetration is usually inclined to circularity due to the surface tension of viscid liquid. On the basis of the surface model, an algorithm of generating the gas channel mesh semi-automatically based on maximum inscribed circle of arbitrary polygon was put forward by combining selecting the path of gas channel manually and calculating the parameter of gas channel node automatically, which greatly increase the practicability.In this paper, viscosity of gas and heat transfers in gas penetration region are neglected. Thus a mathematical model governing the behavior of melt flow and gas penetration is established based on theory of viscous fluid mechanics. Gas penetration extent is described by gas penetration thickness ratio. When control equations and boundary condition equations are made dimensionless, dimensionless pressure is defined as the ratio of melt pressure and surface tension on unit length interface. Therefore, Capillary Number Ca is introduced into dimensionless control equations and boundary condition equations. Matching asymptotic expansion method is applied to solve the equations. By matching these two solutions, gas penetration thickness ratio can be obtained.Considering the influence of gas penetration on melt flow only as boundary conditions of melt filling region, FEM/FDM method is used to solve the temperature, pressure and velocity distribution of melt. Constructing the topology relationship between gas channel node and surface node, the variables in the gas channel mesh could be calculated. Melt flow front and gas penetration front are determined by control volume method. Based on the theoretical study and analysis, a filling simulation system HSCAE/GAS is developed. Simulation results of HSCAE/GAS are proved to be reasonable by comparing with the results of excellent CAE software MOLDFLOW and experiment results.