Factors influencing the warpage in in-mold decoration injection molded composites

This report studied, both experimentally and numerically, the factors affecting the warpage in in-mold decoration (IMD) injection molded parts. All experiments were conducted on an 80-ton injection-molding machine. The materials used in the experiments included poly(ethylene terephthalate) (PET) films and 30 % glass fiber-filled PET resins. U-shaped plate parts with three different angles (908, 1358, and 1508) at the corners were molded. The influence of various processing parameters on part warpage was investigated using an experimental matrix, with its design based on the experimental-parameterdesign method developed by Taguchi. The experimental results suggested that all molded parts warped toward the side of the decoration film. For the parameters selected in the experiments, the corner angle and the melt injection pressure were found to be the principal factors affecting the warpage of IMD injection molded parts. The 908 angled parts exhibited the greatest amount of warpage, while the 1508 angled parts showed the least amount of warpage. Additionally, a commercially available code (Moldex&® 3-D) was used to simulate the temperature distribution during the filling process and the molded part warpage. Calculated warpage satisfactorily matched with the experimental data. It has been shown that the warpage of IMD injection molded parts is mainly caused by the imbalanced temperature distribution during cooling, due to the part geometry and the decoration films.