Numerical simulation and experimental investigation of mold filling and segregation in low-pressure powder injection molding of metallic feedstock

Abstract

The mold filling stage of the low-pressure powder injection molding process and the segregation of the injected part were numerically simulated and validated by an experimental approach. The numerical simulations were performed using the Autodesk Moldflow Synergy 2019 package to specifically investigate the injected length, the front velocity, the filling time, the pressure, and the shear rate, as well as to assess the magnitude of powder segregation after an injection. Furthermore, thermal and rheological characteristics of feedstock were experimentally measured to establish the constitutive equations to be provided to Moldflow. Numerical simulation results were validated with real-scale injections (with feedstock temperatures varying between 80 and 100 °C), using a laboratory injection press. Experimental characterization and injection were conducted using a feedstock formulation based on 17–4 PH stainless steel powder (60 vol% of powder) combined with a low-viscosity binder system. The injected length, the melt front velocity, and the filling times predicted by the numerical model were in good agreement with the experimental observations, with relative differences varying from 3.1 to 4.4%. Since the injections were performed and simulated at constant volumetric flow in a constant cross-section mold cavity, the mold filling results confirm that the feedstock temperature has no influence on the injected lengths, but rather, on the injection pressure. Moldflow also captured the absence of segregation occurring during injection, with experimental measurements of the local solid loading confirming the ability of the numerical model to successfully predict the homogeneous distribution of the powder (i.e., no segregation) within a simple shape mold cavity. Although theses interesting simulation capabilities of the injection and segregation behaviors were obtained for simple-shape components, the present work represents, to the best of the authors’ knowledge, the first simulation of low-pressure injection molding of metallic feedstock.