Simulation Of The Packing And Cooling Stage In External Gas-assisted Injection Molding

External gas-assisted injection molding(EGAIM) can produce plastics parts with no sink mark exists. It has a wide application prospect. The packing process of EGAIM has a vital influence to sink mark of the final products.The mechanism of EGAIM still requires further investigation.In this paper, the numerical simulation method of sink mark in the EGAIM packing process were investigated. Main work and achievements are as follows:(1) Mechanism analysis: Physical phenomena such as the sink mark diminution and polymer phase transformation after gas pressure maintaining in the EGAIM packing process were firstly described. Then, based on the basic control equations of computational fluid mechanics, the control equation of the 3D non-isothermal compressible packing process of the polymer melt was established, with the changing factors of the phase transformation field deduced. Based on the combination of mechanical experiments and theories, the nonlinear viscoelastic constitutive model of materials in the packing process was bulit.(2) Simulation analysis: The simulation of the packing process of EGAIM was investigated. Finite element methods were adopted to disperse and solve the algebraic control equation set. The general nonlinear finite element analysis software LS-DYNA was used as the platform. Based on the user-defined material module UMAT of LS-DYNA, the programming realization of the mechanical model of ABS was conducted. The ALE algorithm was used to solve the coupled velocity-pressure field. Based on the Lagrange method, the flow front of gas was traced, while the phase transformation of the polymer was traced by adopting the Darcy’s law and the fluid volume function(VOF). Thus, the sink mark evolution result of the product during the EGAIM packing process was obtained.(3) Experimental verification:According to experimental results, the influence regularity of different gas packing pressure and duration on the product sink mark was compared, with the feasibility of the simulation method validated.In this article, through numerical simulation research of the packing process of EGAIM, surface morphology and melt the action of the gas phase transition process of had been tracked, and obtained the changing process of sink mark.To a certain extent, it can guide the industrial application.