| With the rapid development of injection-molded parts in different fields, products are usually requested to have high precision and complicated shapes. However, defects affect performance of parts. To reduce the cost and time, it is important to measure and simulate residual stresses and shrinkage of the injection-molded parts. There are evidences indicating that the residual stress and shrinkage is produced due to pressure, temperature change etc. during packing and cooling stage. In this study, the numerical analysis of residual stresses produced during the packing and cooling stage of injection molding and shrinkage after ejection was carried out. The major work and main conclusions are as following:1. Based on the fluid mechanics and flow characteristics of polymer melt in cavity, using time-temperature equivalence, the reasonable simplification and hypothesis were introduced. The mathematical model of residual stresses produced during the packing and cooling stages of injection molding was established.2. In order to verify the numerical results obtained from the developed program, the simulation results were compared with the experimental data for PS. The residual stress of parts during packing and cooling stages was analyzed by changing the process conditions. The results showed that as the packing pressure increases, in-plane residual stresses becomes large, the width of the central parabolic portions in the residual stress profile increases with the mold temperature, the injection velocity and melt temperatures nearly has no effect on residual stresses.3. The mathematical model of shrinkage was established and shrinkage of the injection molded parts was analyzed for PS. The shrinkage decreases as the packing pressure, mold temperature and melt temperature increase. Injection velocity nearly has no effect on shrinkage. The results showed that the predicted shrinkage was found to be reasonable to describe the effects of processing conditions well. |
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