A new starch-based binder for metal injection molding

A composition of starch and linear low-density polyethylene (LLDPE) was prepared as the binder and a mixture of this binder with 316L stainless steel powder was used to achieve a feedstock with 57% vol. powder loading. Rheological specifications of the binder and the feedstock were observed by means of capillary rheometery. Pseudo-plastic behavior of the binder and feedstock was investigated as a necessity in metal injection molding (MIM) process by proper flow characterization tests and their viscosity as the most significant flow characteristic was obtained in acceptable ranges. Thermogravimetric analysis (TGA) was carried out on feedstock in order to understand decomposition behavior of the binder components. In the next step, injection molding of the components was successfully conducted. Mechanical properties of compacts were then investigated through the triple point flexure test and the results showed that mechanical strength of specimens are very close to established ranges. The density of green parts was measured to assess the compaction of feedstock and it was achieved within the expected range for ferrous-based feedstocks. Debinding process was accomplished on compacted articles at three different temperature ranges including 70, 80 and 90 °C. Sintering process also was successfully accomplished on samples. For observing microstructures, the surface and cross section of specimens were compared before and after debinding as well as after sintering using scanning electron macrograph (SEM). Generally, this newly developed binder demonstrated a good potential for being utilized in MIM process.