Effects of cooling strategy on the shrinkage characteristics and its applications to the accuracy control of injection molding
Polymer materials would have shrinkage problem in heating processes, particularly in injection molding process. With the development of modern industry, the needs of high-precision product are increasing. As the result, the accuracy control has become an important issue. This study has investigated the effects of cooling rate on the internal structure and shrinkage characteristics of polymer products. Three kinds of cooling strategy, low temperature cooling, high temperature cooling and reginal different rate of cooling, are used during the injection molding of cylinder product. Products with different cooling strategy are investigated for finding the relationship between shrinkage characteristics and the crystalline structure of the products. The experimental materials are PA66 (T_g>T_r) and PP (T_g<T_r). Experimental results show that the crystallinities of both PP and PA66 cylinder products with high temperature cooling(80℃) are higher than that with low temperature cooling(10℃). As closer to the middle zone of cylinder wall, the crystallinity becomes higher. And the crystallinity of product with reginal different rate cooling(inside 10℃ outside 80℃) is between product with high temperature cooling and low temperature cooling. For the comparison of shrinkage, the shrinkage of PP cylinder with low temperature cooling is 8.78%, which is lower than the10.17% of high temperature cooling. The shrinkage of PA66 cylinder with low temperature cooling is 5.39%, which is higher than the high temperature cooling’s 4.96%. About uniformity of whole inside radius, low temperature cooling is better than high temperature cooling.