Simulation-Based Studies On Processing Optimization And Part Performance In Injection Molding

The behavior and performance of polymer parts are mainly determined by its processing. It's one of frontiers in the field of polymer processing to study on the detail variations of processing conditions, predict quantitative relations among the different physical fields and realize the optimization and control of the system based on the numerical simulation.The present dissertation pays attention to the polymer processing simulation, the design sensitivity analysis, the optimization of processing conditions and the performance of molded parts in the injection molding. The mathematical models and numerical algorithms are developed for the dynamic simulation of the polymer processing, as well as the design sensitivity analysis; the modern optimization algorithms and numerical simulation are integrated to optimize processing conditions; the quanti-tive relations between processing conditions and mechanical behaviors of molded parts with or without weldline are studied. The main results are as follow:1. Following the principles of conservation of mass, momentum and energy of incompressible or compressible viscous flow, the dimensions of physical and geometrical variants in filling and packing phase are analyzed in detail, and the pressure and temperature governing equations for both stages are obtained. The theory can deal with the thin three-dimensional parts of complex geometry.2. A hybrid finite-element/finite-difference method is employed to solve the pressure and temperature fields, and the control-volume method to track moving melt front. The results of filling and packing simulation can predict not only the locations of weld line and air trap, the injection and packing pressure, volumetric shrinkage etc., but also the variation of physical fields, such as temperature, pressure and shear rate etc., at different points and different time steps.3. Based on the governing equation of filling stage, a continuous transient design sensitivity method is firstly developed and applied to injection molding. The sensitivities of pressure, temperature and velocity with respect to a design parameter are calculated.4. A genetic algorithm integrated with numerical simulation is used to optimize injection velocity, and some optimum points and flow rates in ram-stroke are determined. Applying the proposed computational tool in a realistic test case,a significant improvement of the quality, reducing by approximately 50-70% the flow unevenness, is achieved.5. The tensile strength of injection molded PA66 (Zytel 70G33L) parts with weld lines, with different obstacle size in cavity and at the same processing conditions, are studied by both numerical simulation and physical test. It is found that the critical factor that affected the weld line strength is the healing angle of two-melt front, the larger the angle, the higher the strength of weld lines.6. An L9 experimental matrix design based on Taguchi method are conducted to optimize the injection molded part strength with or without weld lines. Four factors, viz. injection pressure, melt temperature, injection rate and packing pressure, are selected in the experiments. The optimum tensile strength and processing conditions are predicted and a good agreement with the experimental results is obtained.This dissertation is part of the project of Research on the Polymer Processing-Evolution of Microstructure-Part Quality Control Based on Numerical Simulation, supported by The National High Technology Research and Development Program (863 Program).( 2002AA336120)...