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AMPM2017: Metal powder recycling
AMPM2017: Understanding the impact of powder reuse in metal Additive Manufacturing Project1_Layout 1 9/7/2016 11:40 AM Page 1
An issue of significant current interest to the AM world, which can potentially impact both the quality and cost-effectiveness of built parts, is whether there is a limit on the number of times that metal powders can be cycled around an AM process. In this article, Dr David Whittaker reviews three presentations on the topic from AMPM2017, the fourth annual Additive Manufacturing with Powder Metallurgy Conference, held in Las Vegas, USA, June 13-15, 2017.
The first reviewed presentation on this subject was given by Lucy Grainger (Renishaw plc, UK) and further supported by reference to a relevant Renishaw White Paper on the subject. The presentation began by underlining that the properties of the powder, and the machine parameters that are used to process it, are closely related. The chemical and physical properties of the powder are therefore critical. Only a small proportion of the powder that is laid down in a build process is actually melted into a component, with most being left unmelted and therefore available for reuse. If unmelted powder was to be considered as contaminated and, therefore, unfit for reuse, then the cost of additively manufactured parts would likely be prohibitive for the vast majority of applications. Renishaw AM systems use an inert argon atmosphere, which is generated by first creating a vacuum
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and then backfilling with the inert gas. Builds generally start at a low oxygen content of <1000 ppm, with the possibility of a starting atmosphere of <100 ppm if required. The oxygen
content in the chamber drops to approximately <10 ppm after the first few layers. For the main reported study, builds began at <1000 ppm oxygen content. For titanium powder,
Hall flow
Shape/morphology
Volume (%)
Understanding the effects of metal powder reuse in laser Powder Bed Fusion
Density/packing
16 14 12 10 8 6 4 2 0 0.01
0.1
1 10 100 Particle size (μm)
1000 3000
Particle size distribution (PSD)
Fig. 1 Important physical properties of metal powders for AM include shape/ morphology, particle size distribution (PSD), density/packing and flow [1]
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