Mold filling simulation and experimental investigation of metallic feedstock used in low-pressure powder injection molding

The mold filling stage of the low-pressure powder injection molding process was simulated numerically and validated by experimental injections. For this, a feedstock formulated from a 17-4PH stainless steel powder (60 vol.%) and a wax-based binder system (40 vol.%) was used. The feedstock was characterized to obtain its thermal properties and rheological profiles at different temperatures. These were then implemented into the Autodesk Moldflow Synergy 2019 package, the numerical tool used for the simulation. The numerical results, including those pertaining to the injected length, the melt front velocity, and the pressure, were validated using a laboratory experiment set-up made of an injection press and two instrumented molds. The injected lengths predicted by the simulation were similar to the experimental short-shot results, with a relative difference below 0.5%. Since the injections were performed at constant volumetric flow, the injected length was not influenced by the feedstock temperature, but only by the shape of the mold cavity. Numerical and experimental results for the pressure were also compared. The agreement between the was good except at the end of the injection process. It is conjectured that the disagreement observed might be due to a difference in boundary conditions. The physical mold not being “air-tight” as the numerical one, an excess pressure could have been present in the latter. As a final note, this interesting simulation capability to predict the injection pressure experienced by a low-pressure (metallic or ceramic) powder injection molding feedstock was, to the best of the authors’ knowledge, for the first time, validated experimentally in this study using a low-pressure sensor placed in the mold during real-scale LPIM injections.