Visualization analysis of large elongated cells formation process at the boundary area between foamed and non-foamed layers in microcellular injection molding

Microcellular injection molding products have a sandwich-like structure where non-foam layers of the surface side surround a foam layer. With small shot sizes, a layer (Core layer I) where many large elongated cells are distributed is formed in the boundary area between the no-foamed layers and foamed layer. These large cells cause deterioration of product strength. As the formation process of this Core layer I has not been clarified, in this study, the authors attempted to observe the behavior of bubbles formed near the cavity surface using a glass inserted visual mold to clarify the formation process of Core layer I. The shear rate was calculated from the observed bubble velocity. The movement, deformation, and breakup of large elongated bubbles were confirmed in the high shear rate region. Moreover coalescence of the bubbles was found to occur in the high shear rate region. We propose a formation model of Core layer I based on the following results: (1) In the high shear rate region, bubbles were elong...