Prediction and measurement of residual stresses in injection molded parts |
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| Authors: | Young Il Kwon Tae Jin Kang Kwansoo Chung Jae Ryoun Youn |
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| Institution: | (1) School of Materials Science and Engineering, Seoul National University, 151-742 Seoul, Korea |
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| Abstract: | Residual stresses were predicted by a flow analysis in the mold cavity and residual stress distribution in the injection molded
product was measured. Flow field was analyzed by the hybrid FEM/FDM method, using the Hele Shaw approximation. The Modified
Cross model was used to determine the dependence of the viscosity on the temperature and the shear rate. The specific volume
of the polymer melt which varies with the pressure and temperature fields was calculated by the Tait’s state equation. Flow
analysis results such as pressure, temperature, and the location of the liquid-solid interface were used as the input of the
stress analysis. In order to calculate more accurate gap-wise temperature field, a coordinate transformation technique was
used. The residual stress distribution in the gap-wise direction was predicted in two cases, the free quenching and the constrained
quenching, under the assumption that the shrinkage of the injection molded product occurs within the mold cavity and that
the solid polymer is elastic. Effects of the initial flow rate, packing pressure, and mold temperature on the residual stress
distribution was discussed. Experimental results were also obtained by the layer removal method for molded polypropylene. |
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| Keywords: | Injection molding Residual stress Hybrid FEM/FDM scheme Layer removal method Stephan problem |
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