Page 33 - 3D Metal Printing Winter 2019

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flowability. The ultimate goal: Find a test that describes how consistently the powder will flow (by recoating mecha- nism, gravity, etc.) and pack down across the build area. Significant investment in powder rheology methods has resulted in a better way to compare the physics of how the powder flows and moves inside the machine. While I have not yet seen a powder rheology requirement in a specification, this area will continue to evolve over the next few years.
Powder always is tested in its virgin state before shipping to the user. How often testing occurs after shipping depends on user/customer specifica- tions. Some users build strictly by num- ber of reuses—not testing the powder and scrapping it once it reaches a specif- ic reuse number. Others employ an internal system that takes a powder sample before each build, testing the sample each time for specification con- formance, which then gets reported back to the end user.
The powder-bed-fusion process, like other manufacturing technologies, pres- ents many variables. The interaction of powder properties and handling meth- ods, and the impact on final part quality are topics that will continue to evolve and stay relevant to all users of the tech- nology. For now, the best way to maintain quality: purchase, handle, store, recycle and test the powder as consistently as possible. Everyone in the value chain— powder manufacturer, supplier, machine OEM and end user—has a shared responsibility in strengthening the knowledge base, identifying significant variables and controlling processes.
While the industry continues to push boundaries with new powder-manufac- turing methods, modified test require- ments and improved handling tech- niques, one constant remains: Powder quality, with all of its complexities, is a top priority as users focus on cost and the quality impact of powder on final-
part production.
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