Abstract: A new supercritical fluid assisted microcellular injection molding technique and the corresponding supercritical fluid generation, measurement and monitoring systems are developed. The supercritical fluid assisted microcellular injection molding test line is constructed. The melt foaming behaviors in supercritical fluid assisted microcellular injection molding are investigated. The results show that the melt foaming process in supercritical fluid assisted microcellular injection molding contains two processes:"foam during injection" and "foam after injection", respectively corresponding to the two different cell morphologies of distorted ellipsoidal cells and the regular spherical cells in the microcellular injection molded parts. The cells formed in "foam during injection" process are stretched by the shear flow and fountain flow behaviors, then broken, pushed out and turned over to both sides of the melt flow front, and finally contacted with the cold mold cavity surface and solidified to form surface bubble marks on the molded parts. The revealed foaming processes and defects generation mechanism have higher reference significance and engineering application value for technological principle and quality control of microcellular injection molding.

Key words: foaming behavior, melt, microcellular injection molding, supercritical fluid