Rheological Characterization of Powder Mixture Including a Space Holder and Its Application to Metal Injection Molding

Abstract

Metal injection molding (MIM) with the space holder technique is becoming one of the important fabrication methods for a net-shape production of micro-sized, porous, complex-shaped metal parts. For a successful injection molding step, rheological behavior of MIM feedstock is essential, which includes peculiar characteristics, such as a wall slip phenomenon. SUS 316L stainless steel powder, binder systems (paraffin wax, polypropylene, polyethylene, stearic acid) and three different sizes of spherically-shaped polymethyl methacrylate (PMMA) as a space-holder were used for this study. The porosity was controlled by varying the volume fraction of the space holder and a total of six different feedstocks were prepared. Rheological characteristics of the feedstock was investigated, especially on viscosities, including wall slip quantification by using a capillary rheometer. By thermogravimetric analysis, the debinding process for completely removing the space holder was proposed. Finally, the shrinkage and porosity of the tensile specimen produced through the sintering process were analyzed and the ultimate tensile strength was obtained.