Feedstock for micro powder injection molding

Abstract

Powder injection molding (PIM) is a viable method for producing complex shaped parts at competitive cost. The PIM process consists of four processing steps: feedstock formulation (mixing), injection molding, debinding and sintering. The PIM process uses a combination of powder metallurgy and plastic injection molding technologies to produce net-shape metal, ceramic or hard materials components.

In this final year project, an investigation and study of the characterization of four different binder systems on molded and sintered parts were carried out. The binder systems comprising of paraffin wax (PW), stearic acid (SA) and varying low density polyethylene (LLDPE) and high density polyethylene (HDPE) were mixed with 316L stainless steel powder having an average size of 2 μm.

Characterizations of the four feedstocks of different binder system were done through differential scanning calorimetry (DSC) and scanning electron microscope (SEM). The four feedstocks were molded into circular disc with micro structures and subsequently debounded debinding and sintered.

Feedstock with higher weight percentage of HDPE will give rounder and incomplete end corners. Feedstock 2 with sintering at 1300 °C with 25% LLDPE and 18% HDPE is the best feedstock for molding the micro structures. Sintering temperature of 1300 °C was concluded to be the best sintering temperature from this binder system combination.

Feedstock 1 and 4 were then used to mold micro gear. Both feed stock were found to be suitable. Edges of the gear teeth with relative good sharpness were produced when feedstock 1 was sintered at 1300 °C and when feedstock 4 was sintered at 1300 °C. However, minor visual defects were observed on both feedstocks.