A new insight into foaming mechanisms in injection molding via a novel visualization mold

Abstract

The complex mechanisms of bubble nucleation and dynamics in foam injection molding have not been uncov- ered despite many previous efforts due to the non-steady stop-and-flow nature of injection molding and the non-uniform temperature and pressure distributions in the mold. To this end, a new visualization mold was designed and manufactured for the direct observation of bubble nucleation and growth/collapse in foam injection molding. A reflective prism was incor- porated into the stationary part of the injection mold with which the nucleation and growth behaviors of bubbles were suc- cessfully observed. The mechanisms of bubble nucleation in low- and high-pressure foam injection molding, with and without the application of gas-counter pressure, was investigated. We identified how the inherently non-uniform cell structure is devel- oped in low-pressure foam injection molding with gate-nucleated bubbles, and when and how cell nucleation occurs in high-pressure foam injection molding with a more uniform pressure drop.