射出成形品に生ずる物性値分布の予測手法の検討(3)

厚肉射出成形品の物性値分布を考慮したそり解析

抄録

The material properties within injection molded products may display a distribution or anisotropy due to the influence of the resin flow velocity distribution profile and the cooling rate during the injection molding process. As a result, the products may warp. From the standpoint of production efficiency, it is very important to predict such warpage prior to the injection molding process, and injection molding CAE tools are widely used at present to conduct warpage analyses.
Warpage analysis techniques currently available do not provide sufficient accuracy because they cannot predict the distribution of material properties that occurs in the interior of injection molded products. This is especially true for thick injection molded products, which display a large distribution of material properties across their thicknesses. As that distribution is thought to affect warpage substantially, the accuracy of the warpage analysis presumably declines even further.
In this research, a thick flat plate was injection molded from a medium density crystalline polyethylene material, and the distribution of the thermal expansion coefficient was measured along the thickness of the molded part. The molecular orientation ratio and crystallinity were also measured and their correlation was examined in order to investigate a method for predicting the thermal expansion coefficient distribution. The results revealed that the thermal expansion coefficient displayed a large variation and anisotropy in the thickness direction and that the distribution correlated with the crystallinity. Moreover, using the thermal expansion coefficient data obtained by these measurements, a material property database was created for use in conducting warpage analyses that take account of the distribution of material properties along the thickness of injection molded products. A multi-layer analysis model was then used in an effort to improve warpage analysis accuracy. The results indicated that warpage analysis accuracy was improved, which shows that a multi-layer model that takes account of the distribution of material properties is effective in conducting more accurate warpage analyses.