CHARACTERIZATION AND SIMULATION OF MACROSCALE MOLD-FILLING DEFECTS IN MICROMINIATURE POWDER INJECTION MOLDING

Abstract

While micromolding with polymers has met with success, material homogeneity remains a critical issue in powder injection molding (PIM) because separation of the powder and binder results in defects in metal or ceramic microparts. Material heterogeneity, or an inhomogeneous particle distribution, in green parts is related to inhomogeneous feedstock mixtures and to powder/binder separation occurring in melt flow. This is a major issue in micro-minature powder injection molding (mu PIM) because of the small particle sizes and high mold-flow velocities in filling. Also, small and irregular-shaped particles tend to agglomerate in the feedstock and fast mold filling may enhance particle migration because of the increased shear-rate gradient in the cavity. These issues prompted this study on the influence of material, processing conditions, and component geometry in the evolution of problems due to homogeneity in microparts such as microchannel arrays (MCAs). The present work focuses on characterization and application of simulation techniques to understand the origin and evolution of macroscale moldfilling defects during mu PIM.