Study On Gas Penetration During Gas-Assisted Injection Molding

A new molding technique, gas-assisted injection molding (GAIM) which is capable of produced 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. Despite some lacunas 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 cool time are decreased, the pressure packing time is eliminated. It is propitious to reduce parts cost.â‘¡GAIM can reduce the clamp tonnage greatly. During the CIM, clamp tonnage must 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 saved.â‘£GAIM can eliminate the lacunas of parts greatly. Part quality can be improved by reducing residual the stress, warpage, sink marks and shrinkage that are normally encountered in CIM.Focused on the formation mechanism of gas bubble blemish inside the gas channel wall for a GAIM part, the main study results are summarized as follows:1.Numerical model is foundedIn this study,a physical model and process simulation of non-isothermal GAIM has been developed based on the time-dependent kinematics of interface evolution,together with the Hele-Shaw approximation.The numerical simulation of the gas penetration behavior during GAIM is a transient moving-boundary flow problem.In the GAIM process the domain of computation is bounded in a part by the unknown a priori moving boundaries.The shape of the moving interface must be determined as a part of the solution.A number of iterations are usually required in order to track accurately the shape of the moving boundary.The generally formulations for primary and secondary gas penetration was solved in order to make better understand of the GAIM part'gas penetration.2. Research on effect of gas-assisted injection molding processing parameters on parts gas penetrationGas penetration in GAIM parts are investigated with the methods of numerical simulation and orthogonal experiment in the paper. The influenced connections of four different processing parameters are studied, such as shot size, gas delay time, gas injection pressure, melt temperature. It shows that the most important processing parameters that influence gas penetration is gas delay time, mold temperature and gas injection pressure and shot size orderly. Therefore, it's particularly important to choose reasonable gas delay time,melt temperature and gas injection pressure.3.Research on effect of gas-assisted injection molding processing parameters interaction on parts gas penetrationThe influenced connections of three different processing parameters interaction were studied, such as melt temperature and gas delay time, melt temperature and gas injection pressure, Gas delay time and gas injection pressure. The results show that: compared to others, Melt temperature and gas delay time interaction is more serious to gas penetration influence. Consequently, it is very important to choose an appropriate couple of melt temperature and delay time.