Molding Properties and Causes of Deterioration of Recycled Powder Injection Molding Feedstock

To lower the manufacturing cost of powder injection molded products, the gate, runner, sprue, and green parts with defects are usually recycled. Unfortunately, these feedstocks deteriorate as the number of recycling iterations increases. This study presents an investigation of the molding properties and the causes of the deterioration of the recycled feedstocks by monitoring changes in melting points, in-situ strength changes during solvent debinding, spiral length, and viscosity. The oxygen content measurements indicate that serious oxidation occurs after recycling, particularly in the paraffin wax (PW). The results of the molecular weight from gel-permeation chromatography (GPC) also show that the polyethylene (PE) deteriorates during recycling. The viscosity of the 1R (recycled once) feedstock was slightly lower than that of the fresh material. However, as the number of recycling iterations increased, the viscosity increased again. As a result, the spiral length decreased and the required injection pressure increased. It was also noticed that more defects developed along the molding and debinding process.