射出成形品の邪魔ピンまわりに生じるウエルドの発現機構に関する研究

充填流動および温度分布の可視化

抄録

In this paper, weld line formation in injection molding is precisely studied with a high speed camera system and infrared thermography. In the filling stage of the injection molding process, polymer melt injected into the mold cavity is simultaneously cooled by the cold mold wall. As is generally known, viscosity of the polymeric material is a function of temperature and time. Therefore it is considered that weld line formation of molded products is not only governed by the melt flow condition during the filling stage, but also affected by the thermal history of the melt in the cavity. In this study, the flow condition and temperature distribution of the melt around an obstructive pin was visualized and measured with a high speed camera system and infrared thermography. Polystyrene was used as the molding material. In the experiment, transmission interference optics was used to visualize the melt flow with the camera system. The temperature distribution of the melt around the pin was measured with thermography. By using these equipment, the formation process of the weld line structure behind the pin and the effect of the molding conditions on the weld line shape were precisely investigated. As a result, it was clearly shown that the obstructive pin inserted in the mold cavity not only disturbed the melt flow condition, but also affected the temperature distribution within the melt. It was also found that the cross sectional shape of the V notch formed on the molded surface was governed by the temperature of the molded skin. It was experimentally confirmed that the size of the V notch was significantly reduced when the temperature of the skin was maintained above the glass transition temperature of the material.