Page 12 - 3D Metal Printing Winter 2019

3D AM INSIGHTS
By Rutuja Samant
Powder Recyclability Factors Into Future of Metal Additive Manufacturing
Fact: The cost of metal additive manufacturing (AM) continues to increase, as manufacturers push conventional metal-powder producers to provide specialty powders designed for applications in the aerospace, defense and biomedical sectors. This reality places growing importance on powder-recycling efforts.
Understand Powder Degradation
First challenge: Understanding diminishing powder properties observed with different types of powders after one or more build cycles.
High-temperature powder alloys such as Inconel 718, generally chemical- ly stable over many powder recycles, are limited by physical traits such as mor- phology and flowability when evaluating reusability. As these materials melt at higher temperatures, the material sur- rounding the melt becomes distorted and sintered together, which can make powder particles larger and unusable.
On the other hand, titanium powders are more susceptible to oxygen pickup,
Rutuja Samant (rsamant@ewi.org) is responsible for managing EWI’s AM portfolio at its Buffalo (NY) Manufacturing Works. She serves as interim director of the Additive Manufacturing Consortium (AMC), a collaborative group of industry, academia and national labs advancing metal-AM technology adoption and deployment. In addition, She represents EWI as the R&D lead for the ASTM Additive Manufacturing Center of Excellence, which aims to create a global innovation hub for advancing AM technical standards, related R&D, education and training. Samant has experience in various metal- and polymer-based AM processes. Her area of specialty at EWI is metal AM with a primary focus on electron-beam-melting technology. Her project portfolio includes work for aerospace, medical, defense and nuclear-industry clients, as well as AM material qualification research for multiple metal-powder producers.
and, therefore, can be used only a cou- ple of times before the powder falls out of specification due to high oxygen content.
Thus, understanding the degrada- tion behavior of different types of pow- ders is important for developing stan- dards for powder recyclability that don’t exist today.
In a recyclability study performed with a high-temperature material at EWI, researchers used and analyzed powder through multiple, laser-pow- der-bed-fusion (L-PBF) builds to understand the effects on powder and part properties. Fig. 1 shows a scanning- electron-microscope image of degraded powder after multiple AM runs. Through the course of these builds, satellites attached to larger powder particles started separating out, creating smaller individual particles. Meanwhile, powder particles started fusing together to form agglomerates with particles fragmented into incomplete particles. All of this affected the flow and packing density of the bulk powder, with particle-size dis- tribution widening and the powder’s oxygen content increasing. However, after 13 consecutive builds with the same batch of powder, the powder still
Fig. 1—Powder degradation after multiple laser powder bed fusion builds.
fell within the composition specifica- tions, making it a viable candidate for reuse.
Increase Reusability
Second challenge: Increase reusabili- ty of metal powders, identifying quali- fied techniques to recondition out-of- spec powders and bring them back into the AM ecosystem.
One popular method: Blend virgin powder with re-used powder before each build. This reduces oxygen content of powders (such as titanium), known to be more susceptible to oxygen pickup. It also can control physical properties of
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Fig. 2—Preplasma conditioning
Post-plasma conditioning