Étude expérimentale de la moulabilité et simulation numérique de l'injection à basse pression des mélanges poudre-liant à base de titane

Abstract

Low pressure powder injection molding (LPIM) is a manufacturing process used to produce parts of high geometric complexity while maintaining a moderate manufacturing cost compared to other manufacturing techniques. Its potential is manifested in the shaping of materials that are difficult to handle through the usual processes and whose production cost is relatively high, such as titanium and its alloys. Indeed, its high temperature reactivity with the interstitial elements and the high cost of shaping by material removal can be bypassed through the LPIM process. Numerical simulation is also useful for reducing non-quality costs by predicting the occurrence of defects and avoiding costly real-scale injections to optimize trial and error method. In this context, the impact of low-viscosity binders on the rheological properties of titanium-based feedstocks for the LPIM process and the use of numerical simulation in predicting the appearance of defects will be an objective of this project. To achieve this goal, four (4) formulations with a solid load of 63 vol. % of titanium powder and different fractions of paraffin wax (PW), stearic acid (SA) and ethylene-vinyl acetate (EVA) were prepared. The rheological analysis of these mixtures was carried out at three (3) different temperatures (80, 90, and 100 ° C) and made it possible to choose the best formulation through the moldability index with the model of Weir. The analysis was validated experimentally through injections into a spiral mold giving injected length. These results showed an increase in viscosity by adding more stearic acid, which is an unexpected behavior. This was explained by the increase of the EVA fraction relative to that of PW and / or the decrease in the amount of powder agglomerations following the surfactant effect of SA and the improvement of the homogeneity of distribution of the metal particles, which generates more friction, and subsequently the viscosity increase. Then, the thermal characterization in terms of thermal conductivity and specific heat for the chosen formulation was carried out in order to build the numerical simulation model of the injection. The numerical simulation results were in agreement with the experimental data in terms of injection time, material front shape and prediction of the occurrence of segregation defects. A zone poor in large particles was observed on the injected parts and was explained by the gradient of the shear rate that they undergo during the injection phase. This result has been validated experimentally by the thermogravimetric analysis technique. As a result, titanium based low viscosity blends were used in LPIM for the first time in this project. The results showed good potential in terms of moldability using low pressures and temperatures.

Date	11 Dec 2019
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Vincent Demers (Supervisor)