(195a) Engineering Particles for Successful Additive Manufacturing: The Basics Engineers Should Already Know

Modern additive manufacturing systems (AM) integrate several well-established solids processing unit operations. Examples include mixing, fluidization, powder dosing and spreading, solids handling, classification, spray wetting, extrusion, and sintering or fusion. Among various AM technologies, powder bed fusion (PBF) is one promising approach. Along with most other 3D print technologies, a PBF printer is essentially a miniaturized manufacturing facility in a box, with significant powder processing challenges that must be overcome for robust production performance and part quality [1]. Though additive systems present their own unique set of challenges, established design principles are often overlooked. And as often is the case, full-scale solids processing plants often have poor efficiencies, long start-up times, and large sensitivities to feedstock material property variations [2,3]. Powder bed fusion printers and other AM technologies have not proven to be an exception.

For a feedstock to function properly in an AM process, it must be designed to meet several material characteristics. Some of the most important include powder flowability & cohesion, powder and roll friction, paste and barrel friction, permeability, particle size & shape distribution (PSSD), triboelectric charging propensity, wetting characteristics, compaction characteristics, and melt phase rheology. Material properties of a feedstock must lie within a range unique to the AM technology at hand, providing key solids metrics for engineering of a feedstock formulation.

Much of E&G's recent research has focused on the design of AM powder bed fusion architectures for plastics, energetics, and pharmaceutical materials, supported by several SBIR and matching awards of $2.7 MM dollars from the Department of Defense [4,5], and related prime contractors and industries. From this work, Dr. Ennis will address solids handling and other powder processing challenges faced in AM, especially for PBF based technologies. Key learnings based on engineering particles of a feedstock will be presented, as well as solutions which drive feedstock material properties toward required windows necessary for successful processing, which minimize production build failures in practice.

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[1] Ennis, B.J. et al. (2017), HPC4Mfg Modeling of Powder Dynamics in Metal Additive Manufacturing, Austin, TX. https://hpc4mfg.llnl.gov/pdfs/events/powder2017/Powder_Dynamics_EG_17oct2017_FINAL.pdf

[2] Ennis, B.J., Green, J., & Davies, R. (1994). The legacy of neglect in the US., Chemical Engineering Progress, 90(4), 32-43.

[3] Ennis, B.J. et al. (2008) Section 21: Solids-Solids Operations & Processing. Perry’s Chemical Engineers’ Handbook. Perry, R. H., & Green, D. W. (eds.), New York: McGraw-Hill.

[4] Ennis, B.J. et al. (2017). Navy SBIR Phase I and Phase II Awards. Development of Explosive Feedstock for Commercial-off-the-Shelf (COTS) 3D Printers. Link for award: https://www.sbir.gov/sbirsearch/detail/1625191

[5] "Chattanooga firm to help U.S. Navy figure out how to 3-D print explosives" (2017), Chattanooga Times Free Press. https://www.timesfreepress.com/news/business/aroundregion/story/2017/dec/10/chattanoogfirm-help-us-navy-figure-out-how-3-/458777/