Binder system for STS 316 nanopowder feedstocks in micro-metal injection molding

The stainless steel (STS) 316 nanopowder (average particle size of 100 nm) were mixed with thermoplastic binder system to produce feedstock for micro-metal injection molding (μMIM) by using lost mold method. The combination of paraffin waxes, bee's waxes, carnauba waxes, ethylene vinyl acetate (EVA), polypropylene (PP) and stearic acid were chosen as binder systems with various formulations adopted to attain optimum feedstock properties. Three different kinds of binder systems of EVA-based, PP-based, and wax-based binder system were deeply investigated. It is found that the wax-based binder system performs the lowest viscosity and heat capacity as well as greater pseudo-plasticity than other binder systems. The feedstocks were injected into SU-8 micromold which was fabricated using photolithography technique. The feedstock which was mixed with wax-based binder system performed the smallest deformation. This result inferred that wax-based binder system is appropriate as binder materials for very fine metal powder applied in μMIM. In this paper we also demonstrated the application of nanopowder on sintering process and showed that the sintered part using nanopowder provides less surface roughness than one produced using micron-sized metal powder.