Flow Visualization of Filling with Aid of Colored Billets During Impact Micro-Injection Molding

Abstract

Abstract Injection molding of thermoplastic parts with micro shot-weight has been developed for many Micro-Electro-Mechanical (MEMS) applications. A lab-made high speed impact type micro-injection machine was developed to perform the micro-injection molding. Many phenomena regarding impact micro-injection molding is not clear and needs systematical investigation. In this study, the filling phenomena during impact micro-injection was observed and investigated. Molds of spiral cavity of four different depths were constructed and employed. One side of the cavity was implemented with transparent window to observe the filling, and the filling phenomena were recorded with a high-speed video camera. To aid detailed observation, in the injection sleeve of the machine, sequential transparent and colored billets were inserted. The recorded images of filling flows of the colored melt in the spiral cavity were used for visualization and analysis of the filling with impact-type micro-injection molding machine. It is observed that melt behind from the sleeve will flow through the core of melt ahead and lead the melt front. Fountain flow in high speed micro-injection molding is dominant. During penetration, the colored melt, which is behind the transparent melt originally, is comparatively hot and flows along the core, following the inner side of core to seek shortest flow path.