Développement des mélanges poudre-liant faible viscosité pour la fabrication de pièces métalliques de formes complexes par moulage par injection des poudres à basse pression

Abstract

The cost-effective production of complex shaped metal parts produced in low production volumes is one of the main objectives of the advanced manufacturing industry. Low pressure injection molding of metallic powders (LPIM) is considered to be one of the most promising advanced technologies that simultaneously cover all these technical requirements and directly respond to this scientific problem. This process is particularly suitable for materials that are difficult to shape using traditional processes (e.g. forging or machining), such as titanium, which has strong industrial potential. However, the use of titanium in LPIM being still relatively new, its development remains limited due to limited scientific knowledge on the moldability of feedstocks as well as on rheological models simulating the filling of an LPIM mold. Thus, the main objectives of this project were to quantify the impact of the rheological model on the results of numerical simulations and to characterize the impact of the proportion of the different constituents on the moldability of the titanium-based feedstocks. In the first part of this work, two (2) LPIM feedstock were characterized and then simulated using three (3) distinct rheological models (Cross-WLF, 2nd order and matrix). The experimental results made it possible to confirm that the rheological model must be chosen according to the shear-thinning behaviour of the feedstock to be simulated, where the one of the LPIM titanium-based mixtures was better described by a second-order model. Note that the conclusions of this first part were summarized in a first scientific article. In the second part of this work, thirty-five (35) mixtures with a solid loading varying from 60 to 72% vol. and varying proportions of paraffin wax (PW), stearic acid (SA), ethylene vinyl acetate (EVA) and carnauba wax (CW) have been prepared. The rheological analysis of these mixtures at three (3) temperatures (80, 90 and 100 ° C) made it possible to calculate a moldability index for each feedstock with the Weir model, whose analysis has been validated experimentally through injections into a spiral mold giving the length injected. These results led to the conclusion that a polymeric binder containing 1% vol. of SA, 1% vol. of EVA, 3% vol. of CW and the PW balance provides the best compromise between moldability, demolding and segregation. Preliminary injection tests into the cavity of a complex mold have shown that a volume fraction of powder of 64% is the maximum to ensure complete filling of the part and to limit surface defects. Then, the injection of two feedstocks with low and high moldability (60 and 64% vol., respectively) were simulated numerically in a mold with complex geometries. The results of these simulations in terms of prediction of the solidification front are in good agreement with the experimental validation, confirming the possibility of simulating the injection of a part of complex shapes with a mixture based on titanium for the LPIM process. Note that the conclusions of this second part were summarized in a second scientific article.

Date	20 Aug 2020
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Vincent Demers (Supervisor)