Numerical Simulation Of Residual Stresses In Injection Molded Products

The injection-molded products, due to the influence of various factors such as viscoelasticity of the polymer, non-linear changes of process parameters, flow orientation, pressure gradient in cavity, non-uniform cooling and the mold elasticity deformation, after undergoing the filling, packing, cooling and ejection stages, its quality is hard to control. Among the quality defects, the form and subsistence of the residual stress is one of the most important reasons, which directly results in the shrinkage and warpage. Therefore, if we can figure out the development law of the residual stress and establish an effective calculating model, it will boost the research of this field and highly improve the products qualities. This thesis is concentrated on the experimental analysis of amorphous material ABS and the calculation of residual stress in the solidification stage. The main works are as follow:1. Based on the mechanism of the injection molding, via proper hypothesis and simplification, the research approach and numerical computation model for the analysis of residual stress was established, including the start and end computational time, initial and boundary conditions, and so on. Then the finite difference method (FDM) was further employed to simulate the development of the residual stress in solidification stage, using one-dimensional mathematic model and considering creep viscoelasticity of the high polymer. The residual stress and in-mold strain before ejection were analyzed in thickness direction. The final shrinkage and warpage results were also given.2. The viscoelasticity behaviors between the solid and liquid stages are very different, so viscous coefficient of liquid cannot be simply used in the solid condition. To obtain the suitable viscoelasticity data for our analysis, an inversion model was suggested to calculate the creep parameters under solid condition by comparing the theoretical calculation and experiment. By analyzing the part creep during the cooling procedure, the residual stress distribution was determined.3. The shrinkage and warpage of ABS, a kind of thermoplastic amorphous material, was studied through experiment. The influence of packing pressure, mold temperature and...