Microcellular injection molding of foamed engineering plastic parts with high dimensional accuracy

Abstract

Polyformaldehyde (POM) and Polyamide 66 (PA66) are engineering plastics with excellent mechanical properties and thermal stability. Producing microcellular injection molded POM and PA66 parts with high dimensional accuracy would be beneficial to reduce material cost and product quality. In this research, foamed POM and PA66 gear parts were fabricated by using microcellular injection molding with supercritical nitrogen as the blowing agent. Compared to conventional injection molded parts (parts that foaming is not involved), the foamed POM and PA66 gear parts achieved 5% and 10% average weight reduction, respectively. The foamed parts displayed a lower shrinkage ratio when compared to the solid counterparts, which was attributed to the cell expansion that offset part of the inward shrinkage stress. Moreover, POM gear parts with a higher crystallinity degree presented more serious shrinkage ratio compared to the PA66 gear parts, which contributed to the denser polymer molecular chains arrangement. The shrinkage ratio in both directions of PA66 foamed gear parts depended on the injection volume, and the lowest shrinkage ratio of 0.043‰ was obtained at the injection volume of 74 mm, when the polymer reached the maximum foaming ratio. The findings from this study could provide practical guidance for preparing microcellular injection molded products with high dimensional accuracy.

Fabrication of polyamide 12T micro‐cellular foams with ultra‐high compressive strength via in situ polytetrafluoroethylene fibrillation using supercritical carbon dioxide foaming

“…Han et al prepared micro‐porous PA6 foam by controlling the crystallization properties and studied its foaming behavior 15 . Feng et al investigated the micro‐porous injection molding of polyformaldehyde and PA66 gear parts using nitrogen as the blowing agent 16 . However, maintaining the cell size at the micron level while achieving high VER through chain‐extension modification is challenging.…”