Study On The Key Techniques Of Gas-Assisted Injection Molding In Automobile Injection Molding Parts

A new molding technique, gas-assisted injection molding (GAIM) which is capable of producing parts having both thick and thin sections, with structured rigidity and not sacrificing surface quality, has received extensive attention in recent years. In this process, molten plastics are injected into a mold followed by an injection of pressurized nitrogen gas into the core of the melt to produce hollow parts. It is a molding plastic technology which is applied in practical phase in developed countries in 1990s and praised epochal technological innovation of injection process. Despite some pitfalls in the practical application of GAIM process, it offers a number of advantages over conventional injection molding (CIM):â‘ GAIM can substantially reduce cycle time. The melt injection time and cooling time are decreased, the pressure packing time is eliminated. It is beneficial to reduce parts'cost.â‘¡GAIM can reduce the clamp tonnage greatly. During the CIM, clamp tonnage must be large enough to meet the needs of packing stage, especially to solve the problem of sink marks. However, the low gas pressure is needed for packing in GAIM, thus, the clamp tonnage is reduced.â‘¢GAIM can save material. The first stage of this process is shot short, so the material is decreased by 10%-50%.â‘£GAIM can eliminate the pitfalls of parts greatly. Part quality can be improved by reducing the residual stress, warpage, sink marks and shrinkage that are normally encountered in CIM. The main study results about the technics, numerical simulation and mold of GAIM are summarized as follows:1. Study on gas penetration of the GAIMThe study concerns the two-phase flow of gas and liquid in the cylindrical channel, the rectangular flow channel , the flow and its governing equation in mold cavity, the interface between gas and melt , the supposition and deduction of the boundary condition, the theoretical formula of the surface melt layer thickness is deduced according to the model of the circular gas channel and the simple discussion of the formula is made, the key technology of the gas channel design is studied, and as a result , the familiar structures of gas channel, the dimension design of different gas channels and the design principles of gas channels are...