熱粘弾性モデルによるポリプロピレン射出成形品に発生する残留応力発生機構に関する研究
Generation Mechanism of Residual Stress during Injection Molding Process
石島 守・山部 昌・下田洋彰・新保 實・宮野 靖
Ishijima, Mamoru / Yamabe, Masashi / Shimoda, Hiroaki / Shimbo, Minoru / Miyano, Yasushi
Products manufactured by injection molding sometimes show unexpected defects and lack of precision in dimensions due to residual stress that occurs during the molding process. In order to optimize molding methods and conditions, it is necessary to clarify the mechanism generating this type of stress. The authors previously proposed a thermo-viscoelastic model with a dual-layered construction to explain the occurrence of residual stress through the thickness of extrusion-molded products made of poly-ethylene. Based on accurate measurements of the material properties, the mechanism generating residual stress through the thickness was clarified in terms of thermally induced and distributions of material properties induced factors. In the present work, the thermo-viscoelastic model has been advanced from a dual-layered to a three-layered model in order to take into account the heat history and layered construction that are typically found in the thickness direction of injection molded products. This model demonstrated the generation mechanism of residual stress during the injection molding process and indicated that the factors inducing residual stress can be divided into the categories of thermally induced and distributions of material properties induced factors. The validity of the model was confirmed by comparing the results of quantitative calculations made with the finite element method and stress measurement data obtained from the layer removal method.
Key words: Injection molding / Residual stress / Thermo-viscoelastic model / Layered structure / Warp deformation