Research On The Mechanism Of External Gas-Assisted Injection Molding GAS-Packing Stage And Its Simulation

External Gas-Assisted Injection Molding (EGAIM) is a kind of advanced plastic molding technology, which can reduce the shrinkage defects of plastic products effectively without sink mark and warp. At present, studies on EGAIM focused on the effects of process parameters on the EGAIM quality at packing stage. And further studies on the mechanism and simulation about EGIAM are of great practical and engineering significance for understanding the effect of EGAIM packing stage process parameters on forming quality and have some guidance for practical production.Firstly, in this paper, EGAIM process is divided into several sub processes and then analyses the physical process, the cause of the sink mark and the influence of reciprocity between gas and fondant in detail. According to the process analysis, the paper points out the limitations of EGAIM using different types of polymer material. The model of EGAIM packing stage is founded based on the physical description and viscous fluid.Secondly, based on the process analysis of EGAIM, the EGAIM packing stage is assumed and simplified, and then get the simple EGAIM flow model and boundary condition. Taking a flat with rib structure as an example, the EGAIM packing stage is simulated by Fluent and gets sets of dates of sink marks condensation layer and morphology of gas acting face. The simulation shows that the model is reliable and the mechanism analysis is correct.Thirdly, the sink marks of ribs and morphology of gas acting face are obtained by oneparameter experiments of gas delay time, gas packing pressure and gas packing time. Comparing the results obtained from the experiments and the corresponding simulations, the depth of shrinkage mark from the simulations is smaller than that from the experiments, but the penetration depth of gas is larger than that from the experiments. The deviations between the FE simulations and the experiments were discussed and the cause of deviations are analysed in this article.At last, aimed at the experimental results and simulation phenomenon, the noncritical factors of EGAIM, such as gas temperature, mode of gas action and the root shape of ribs, are simulated to make sure the influences on molding quality and then compare the molding performances with the simulated experiments derived before and the effects law are obtained that how these factors influence the plastic products.