| Gas assisted injection molding (GAIM) is an innovative multi-component injection molding developed on the basis of traditional injection molding in the 1970's. In GAIM, the mold cavity is partially filled with the polymer melt, followed by the injection of compressed gas. The gas penetrates into the polymer melts and forces them to fill the whole mold cavity. GAIM can realize gas holding and packing, reduce shrinkage and warp-page, get the hollow products in the section, save materials, make mold designing more flexible.However more process parameters, such as melt injection percent in advance, delay time, gas inject pressure in the process, are included in GAIM because two phase flow happens at gas filling time. So how to predict gas penetration and the influence of parameters on GAIM products become the key problem before mould making. In this study, based on the molding filling principle and Theological theories, a mathematical model is established by using generalized Hele-Shaw flow of an inelastic and No-Newtonian fluid under non-isothermal conditions. A hybrid finite element/finite difference numerical scheme is applied to solve pressure field, temperature field, and velocity field etc. Control volume method is used to trace gas/melt interface and melt advancement. Polymer skin fraction and polymer filling fraction are used to describe the melt and gas distribution.The pressure control equation of constant flow front speed is deduced, the relationship between gas pressure and melt front speed was found, and controlequation were verified by numerical simulation.Experiments are investigated to study how various process conditions and parameters influence the process, and comparison results of experiments and numerical simulation verify the program. |
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