Low-pressure metal injection molding is a technique for manufacturing components with the complexity of the molded component but the mechanical properties of wrought component. Unfortunately, traditionally, the optimization of debinding and sintering steps are carried out without having a proper knowledge of the moldability of the mixtures used in the process. Indeed, the understanding of rheological properties properties and segregation of mixtures is still very limited and results in limitations for the LPIM process. The objective of this research project was to characterize the influence of binders on the rheological behavior of mixtures by measuring the viscosity and segregation of low viscosity mixtures used in the process LPIM. To achieve this objective, rheological characterization and thermogravimetric tests were carried out using 12 different mixtures. These mixtures contained 60% of volume spherical powder of Inconel 718, waxes, surfactants and thickeners. The rheological tests were used to calculate the index injectability αSTV of mixtures, while the TGA tests were used to evaluate precisely the segregation of powders in these mixtures. It has been demonstrated that the three (3) mixtures containing wax and stearic acid presented the largest αSTV indexes a good advantage for MIM and a large segregation limiting their use for obtaining good manufactured parts by LPIM. . In contrast, the mixtures containing paraffin wax and ethylene-vinyl acetate and the mixtures containing only carnauba wax segregated little or not at all, but presented very bad indexes αSTV, turning their injection difficult at excessively high pressures for the process studied. The best compromise therefore seemed to be the mixtures containing the wax (paraffin wax, beeswax and carnauba wax) and low content of stearic acid and ethylene-vinyl acetate. Otherwise, the pre-existing physical laws have confirmed the rheological and thermogravimetric results, but also the rheological and thermogravimetric tests have to demonstrated that the segregation occurring during the rheological test produces a meaningful effect in low-viscosity feedstocks. Because the segregation is driven by the time spent in molten state, the effects of segregation on viscosity were visible. The impact of binders and temperature on the rheological properties of feedstocks used in low-pressure powder injection molding was also investigated. The results obtained in this study showed that the viscosity profiles of wax-based feedstocks must be obtained using short rheological test duration to evaluate precisely the flowability of such feedstocks.
Fareh, F. (Author),
Demers (Supervisor) &
Demarquette (Co-supervisor),
15 Dec 2016Student thesis: Master's thesis › Master in Engineering: Mechanical Engineering