Development of an Injection Mold Capable of Melt Flow Control and Induction Heating and Cooling

Weldlines are a type of defect in polymer injection molding and are known to impair the appearance and mechanical strength of the molded product. A previous study involved designing and fabricating an induction heating and cooling mold that incorporates an induction coil, allowing it to rapidly heat up. The study verified that the use of this mold prevents weldlines and improves the surface properties of the molded product. Although it is possible to prevent impairment of the external appearance caused by weldlines or the exposure of glass fibers on the surface when the mold is applied to glass fiber reinforced thermoplastic, the results of the previous study indicated that it did not significantly improve the mechanical strength. Hence, the present study involved designing and fabricating an injection mold capable of melt flow control in addition to induction heating and cooling by incorporating a melt flow control mechanism that employs a movable core pin to control the flow direction in the mold used in the previous study. The mold is used to form samples of short- and long-glass fiber reinforced polypropylene while simultaneously performing heating and cooling and melt flow control to obtain samples with smooth flat surfaces in which the exposure of glass fibers is prevented while exhibiting increased bending strength.