Simulation numérique et caractérisation expérimentale de la phase d'injection du moulage par injection à basse pression des poudres métalliques

Abstract

Injection molding of low-pressure metal powders is one of the most interesting advanced manufacturing technologies to produce complex shaped parts with high properties while being economic at low production volumes. Injection is one of the most important steps in the process of molding low-pressure powder injection molding. During this step, several defects may occur such as filling masks or segregation of powders. Thus, the poor understanding of the influence of the injection parameters on the formation of such a defect today still limits the use of this process on a large scale in the industry. The main objective of this project is to numerically simulate the injection step in a single mold cavity and validate these results experimentally. To do this, some properties of the mixture such as viscosity, specific heat, density and thermal conductivity were characterized and then implemented in the Autodesk Moldflow Synergy 2019 to simulate by the finite element method. the injected length the front velocity of the casting, the filling time, the shear rate and the potential of segregation of the powders after an injection, all results have been experimentally validated by full-scale injections. These different thermal and rheological properties of the mixture were obtained from different sizes of the powder particles (3, 7 and 12 μm) and different morphologies of the powder (spherical and quasi-spherical, atomized respectively by gas and water) using the same polymeric binder formulation (based on wax, stearic acid and ethylene vinyl acetate) and the same stainless steel metal powder grade (17-4 PH). It has been shown that the rheological profiles of all mixtures and the intensity of segregation depend on the shape and size of the powder used in the formulation of the mixture. The injected length, filling times, and the melt front velocity of the numerical model were in good agreement with experimental observations with a small relative difference of less than 4.4%. Since the injections were performed and simulated at a constant volumetric flow rate in a mold cavity of constant cross section, the mold fill results confirm that the feedstock temperature has no influence on the injected lengths. Powder segregation during the injection was also successfully simulated confirming the volume fraction of the powder through the injected part. Experimental injections confirm that the Autodesk Moldflow Synergy 2019 is a powerful tool for predicting the behavior of the mix when filling a simple mold cavity. Thus, the best candidate for the injection is that produced with the gas atomized powder because it admits a high moldability and a low segregation potential compared to the mixtures with the wateratomized powders. To the best of our research team's knowledge, the demonstration of numerical simulation performance of wax-based metal mixtures was performed for the first time in this study (i.e., for all software combined).

Date	26 Nov 2018
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Vincent Demers (Supervisor) & Louis Dufresne (Co-supervisor)