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

• Published in: Express polymer letters 2016-06, Vol.10 (6), p.462-469
• Main Authors: Shaayegan, V., Mark, L. H., Tabatabaei, A., Park, C. B.
• Format: Article
• Language: English
• Subjects: Bubbles; Foam injection molding; High pressure; In-situ visualization; Injection molding; Low pressure; Molds; Nucleation; Nucleation mechanism; Polystyrene; Pressure drop; Processing technologies; Visualization
• ISSN: 1788-618X; 1788-618X
• DOI: 10.3144/expresspolymlett.2016.44

The complex mechanisms of bubble nucleation and dynamics in foam injection molding have not been uncovered 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 incorporated into the stationary part of the injection mold with which the nucleation and growth behaviors of bubbles were successfully 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 developed 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.