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A Visualization Method to Investigate the Mechanism of Cell Nucleation and Growth in High-Pressure Foam Injection Molding
A Visualization Method to Investigate the Mechanism of Cell Nucleation and Growth in High-Pressure Foam Injection Molding
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通用高分子材料
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Introduction
Foam injection molding (FIM) is one of the most promising technologies owing to its ability to
produce low-density parts with high geometrical accuracy and stiffness-to-weight ratio at fast
production cycles [i]. In this technology, a gas-charged melt is being injected into a confined cavity.In low-pressure FIM, i.e. short shot injection, foaming occurs due to the pressure drop over the gate,followed by simultaneous travel and growth of nucleated bubbles till the end of the mold cavity. In high-pressure FIM, on the other hand, a full-shot is injected and the mold cavity is filled completely.The foaming then occurs due to the cavity pressure drop as a result of melt solidification andshrinkage. However, reaching a uniform high cell density microstructure with desired void fractioniS too challenging in FIM due to the complicated thermodynamics and theology, fast kinetics, and the large amount of shearing and elongation involved in this technology. Therefore, the in situ mold visualization, which uncovers the actual behaviour of the melt flow and bubbles formation, is the only practical approach to observe bubbles'' formation and capture their complicated behaviour during different mold filling stages.
