Effect of Stearic Acid on the Rheology and Moulding Behaviour of 316 L Stainless Steel Powder Using Thermoplastic Natural Rubber (TPNR) Binder

In the present study, thermoplastic natural rubber (TPNR) has been developed as a novel backbone polymer to produce a new feedstock formulation for metal injection moulding (MIM) process. In this paper, the effect of stearic acid (SA) on the rheology properties and moulding behaviour has been investigated for the TPNR binder system. Feedstock mixture of 22 μm 316 L stainless steel powder and the binder system consists of three major fractions of paraffin wax (PW), TPNR, and SA with a powder loading of 65 vol. % was investigated. Comparison also been made with existing of palm stearin (PS) in the binder system replacing the PW. The melt rheological behaviour of TPNR blends and the mixtures of the feedstock had been investigated. This study also investigates the effect of moulding temperature on the addition of SA in the binder formulation. The results show that the introduction of 10 vol. % of SA in the binder that act as a lubricant helped in the mixing process to produce a homogeneous blend and the torque reached a steady state value in a short time. The viscosity of the feedstock also has been reduced with the lower injection moulding temperature.