Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore
doi:10.3850/978-981-18-6021-8_OR-06-0086
Towards Effective Powder Reuse in "Large Format Laser Aided Additive Manufacturing" (LAAM)
1Sustainable & Circular Process Technology (SCPT) Group, Singapore Institute of Manufacturing Technology, 2 Fusionopolis Way, #08-04, Innovis, Singapore 138634
2Diagnostic and Measurement Unit, Singapore Institute of Manufacturing Technology, 2 Fusionopolis Way, #08-04, Innovis, Singapore 138634
ABSTRACT
With the extensive implementation of additive manufacturing in industry, it becomes imperative to consider the circularity of metal powder for sustainability; keeping the material in circulation through processes such as reuse and recycling. This is especially so in the LAAM process or other large scale production that requires great quantities of material. Improvement in sustainability is ideally achieved by reusing powders directly in LAAM, but potentially hampered by changes in the powder quality due to the preceding build step. A key factor in powder quality deterioration is thermally driven chemical change that is exacerbated by atmospheric exposure in LAAM due to the necessary use of a fairly open system. Understanding the susceptibility of the material to oxidation under varied thermal histories can help to better assess the powder quality for a given additive manufacturing process and the viability of powder reuse. Thus, in this work, we compared the surface properties of 316L stainless steel powders recovered after the LAAM process to samples exposed to varied artificial thermal ageing conditions to correlate thermal history, oxidation level, and powder condition before potential reuse. The chemical changes were induced by high temperature treatment of the powders in air atmosphere and the resulting surface transformation was quantified by elemental analysis using energy dispersive X-ray spectroscopy. The obtained data were used to create a time-temperature-oxidation level map for the stainless steel powder. Separately, the powder recovered from LAAM was evaluated for changes in particle size, surface oxidation level, and the heterogeneity in the particle surface condition. Finally, the virgin powder was characterised to serve as a baseline. It was observed that significant heterogeneity developed in the LAAM process for the collected powder primarily affecting the apparent presence of contaminants, and particle surface oxidation that varied in a broad range due to variation of thermal history among the particles. In contrast, the artificially aged samples were much more homogenous, as expected, and provided a calibration scale to correlate the oxidation level of recovered powder particles with the likely thermal history of the particles. The quantification of the fraction of particles with significant changes in the recovered powder gave a measure of reusability that could be further combined with macroscopic powder properties to support decisions on the reuse conditions of metal powder in the LAAM process.
Keywords: Additive manufacturing, Powder reuse, Powder recycling, 316L stainless steel
1Sustainable & Circular Process Technology (SCPT) Group, Singapore Institute of Manufacturing Technology, 2 Fusionopolis Way, #08-04, Innovis, Singapore 138634
2Diagnostic and Measurement Unit, Singapore Institute of Manufacturing Technology, 2 Fusionopolis Way, #08-04, Innovis, Singapore 138634
ABSTRACT
With the extensive implementation of additive manufacturing in industry, it becomes imperative to consider the circularity of metal powder for sustainability; keeping the material in circulation through processes such as reuse and recycling. This is especially so in the LAAM process or other large scale production that requires great quantities of material. Improvement in sustainability is ideally achieved by reusing powders directly in LAAM, but potentially hampered by changes in the powder quality due to the preceding build step. A key factor in powder quality deterioration is thermally driven chemical change that is exacerbated by atmospheric exposure in LAAM due to the necessary use of a fairly open system. Understanding the susceptibility of the material to oxidation under varied thermal histories can help to better assess the powder quality for a given additive manufacturing process and the viability of powder reuse. Thus, in this work, we compared the surface properties of 316L stainless steel powders recovered after the LAAM process to samples exposed to varied artificial thermal ageing conditions to correlate thermal history, oxidation level, and powder condition before potential reuse. The chemical changes were induced by high temperature treatment of the powders in air atmosphere and the resulting surface transformation was quantified by elemental analysis using energy dispersive X-ray spectroscopy. The obtained data were used to create a time-temperature-oxidation level map for the stainless steel powder. Separately, the powder recovered from LAAM was evaluated for changes in particle size, surface oxidation level, and the heterogeneity in the particle surface condition. Finally, the virgin powder was characterised to serve as a baseline. It was observed that significant heterogeneity developed in the LAAM process for the collected powder primarily affecting the apparent presence of contaminants, and particle surface oxidation that varied in a broad range due to variation of thermal history among the particles. In contrast, the artificially aged samples were much more homogenous, as expected, and provided a calibration scale to correlate the oxidation level of recovered powder particles with the likely thermal history of the particles. The quantification of the fraction of particles with significant changes in the recovered powder gave a measure of reusability that could be further combined with macroscopic powder properties to support decisions on the reuse conditions of metal powder in the LAAM process.
Keywords: Additive manufacturing, Powder reuse, Powder recycling, 316L stainless steel
