Impact of Mixing State of Gas–Melt Mixture on Foaming Behavior During the Plastication Process in Foamed Injection Molding

ABSTRACT This study employed chemical foaming injection molding (CFIM) technology to dynamically observe the foaming behavior of molten resin using an instrumented mold equipped with a high‐speed camera. The foaming characteristics within the mold cavity indirectly reflected the gas dissolution state in molten resin prior to injection (i.e., the stability of the gas–melt mixture system). Gases generated by the decomposition of the chemical blowing agent (CBA) in the barrel exhibited a tendency to escape from the melt, leading to unstable foaming behavior under identical experimental conditions. However, after the first cycle (30 shots in this study), the foaming behavior stabilized, indicating the establishment of a dynamic equilibrium between gas dissolution and escape. The stability of gases in molten resin within the barrel was systematically investigated through temperature distribution across the front and rear zones of the barrel, the molding cycle, and CBA dosage. The results demonstrated that reducing the barrel temperature, shortening the molding cycle, and increasing the CBA content enhanced the degree of dynamic equilibrium. Lowering the temperatures in Zones 4–5 delayed CBA decomposition to Zones 2–3, reducing gas escape duration and increasing diffusion resistance, thereby elevating the cell count from Grade 2 to Grade 3. In Zones 2–3 (the sensitive decomposition region), temperature reduction improved the cell count from Grade 3 to Grade 4. Shortening the molding cycle from 37 s to 32 s decreased the residence time of the mixture in the barrel, limiting gas escape and increasing the effective gas content, which raised the cell count from Grade 4 to Grade 6. Dynamic equilibrium establishment was observed during CBA dosage adjustment: at 1 wt.% AC blowing agent masterbatch (AC‐BAM) content, the effective gas content decreased with prolonged residence time without achieving equilibrium. When the dosage was increased to 2 wt.%, dynamic equilibrium was established, with further dosage increases enhancing equilibrium stability.