Low-pressure injection moulding of stainless steel powders

Abstract

Powder injection molding (PIM) is a cost-effective technique for producing small, complex, precision parts in high volumes. PIM consists of four main processing steps: mixing, injection molding, debinding and sintering. To reduce the design-to-manufacture cycle time for injection molding, simulation software could be used. To have a good understanding of the PIM process and to provide the necessary data for simulation, characterization of the material is essential. This paper presents the characterization of PIM feedstock consisting of 91 wt.% M2 high speed steel (HSS) powder and 9 wt.% PAN250 polymer binder. The mechanical properties (Young's modulus, Poisson's ratio, in-plane shear modulus), thermal properties (coefficient of thermal expansion (CTE), softening point, transition temperature, specific heat, thermal conductivity) and rheological property of the feedstock were established. The CTE of the molded feedstock in three perpendicular directions differed significantly. Except for the specific heat, the mechanical and thermal results showed that the feedstock's properties were generally closer to a polymer rather than a metal. Rheological results exhibited pseudoplastic or shear thinning flow behavior, where its viscosity decreased with increasing shear rate. The feedstock viscosity also decreased with increasing temperature and was found to be suitable for molding.