Modifying polyacetal binder based feedstock to improve quality of MIM parts

The polyacetal binder system used in preparation of feedstock for powder injection molding is known for its fast debinding rate. However, flow lines and binder-rich zones formed at cavity entrance of an injection molded part are common problems of the feedstock based on this system. In addition, the acid debinding process required for this system involves handling of liquid acid, which needs a special furnace. Modifications of a polyacetal binder based Fe-8Ni feedstock to provide better quality parts and use of thermal debinding were experimented at CANMET. It was found that, by modifying the feedstock, the required molding temperature can be reduced significantly and the above mentioned surface defects on green parts can be completely removed. Furthermore, the green parts made with the modified feedstock have higher green weight and density, and the sintered parts have very uniform surface finish and good dimensional control. More importantly, the debinding can be completed with a thermal debinding process using a regular furnace at a peak temperature of 170 °C.