Abstract: The application of microcellular injection molding process is severely hindered because of the surface defects such as swirl marks and sliver marks caused by cell rupture of the melt flow front in filling process. In order to improve the surface quality of microcellular injection molding parts, a new method to control mold cavity gas pressure is proposed by using high pressure nitrogen pressurizing and high pressure vessel to ensure the mold cavity gas pressure stable. Corresponding mold cavity gas pressure control device and control system are constructed. Gas counter pressure (GCP) microcellular injection molding experiment of a medical device appearance product is designed to study the influence of GCP on surface quality of microcellular injection molding part. The results show that with the increase of mold cavity gas pressure, the swirl marks and sliver streaks are gradually reduced until be eliminated, the surface gloss of part is greatly improved, and the surface roughness of part is reduced significantly. For the selected material ABS, 3 MPa pressure of mold cavity gas pressure is appropriate to produce the microcellular injection molding part with excellent surface quality.

Key words: gas counter pressure(GCP) microcellular injection molding process, surface gloss, surface quality, surface roughness