Study on the Influence of a Glass Cavity Wall on the Melt Flow Behavior in a Glass-Inserted Visual Mold

Abstract

One of the important tasks in the analysis of the molding process is to directly observe the melt flow behavior inside an injection mold. Researchers have proposed visual molds with glass or acrylic inserted into a metal mold. One of the coauthors and his coworkers have developed a “Glass-Inserted Mold”, which was constructed from standard mold parts. This mold can be utilized on any injection molding machine, and it can be operated under usual injection pressures of less than 50MPa. By using this mold, we succeeded in observing the melt flow behavior under high injection rate and high injection pressure that could not be observed by other visual molds. However, up to now, we did not investigate whether the melt in the glass-inserted cavity and that in the metal cavity behave differently from cach other, i. e., whether the differences in the thermal conductivity coefficient, the specific heat, etc. between glass and metal cause different melt flow behavior.In this paper, we propose a method to estimate the influence of the glass cavity surface on the melt flow behavior through comparing weld-line generation patterns, based on a new experimental Glass-Inserted Mold with a wide visible area. With this method, we investigated the above influence on the filling pattern and the pressure distribution. In conclusion, we confirmed that, if the molding experiments of GPPS were carried out with mold temperatures at least 20°C lower than the glass transition temperature of the melt, the influence of the above differences between glass and metal can be neglected.