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Sci Rep. 2019 Mar 25;9(1):5038. doi: 10.1038/s41598-019-41415-7.

Formation processes for large ejecta and interactions with melt pool formation in powder bed fusion additive manufacturing.

Author information

1
The Pennsylvania State University Applied Research Laboratory, P.O. Box 30, State College, Pennsylvania, PA, 16804-0030, USA. arn5000@psu.edu.
2
The Pennsylvania State University Applied Research Laboratory, P.O. Box 30, State College, Pennsylvania, PA, 16804-0030, USA.
3
Moog Inc. 500 Jamison Rd., Plt. 20, East Aurora, NY, 14052, USA.

Abstract

Ejecta with a size much larger than the mean particle size of feedstock powder have been observed in powder bed fusion additive manufacturing, both during post-process sieving and embedded within built components. However, their origin has not been adequately explained. Here, we test a hypothesis on the origin of large (much larger than the mass-median-diameter of feedstock powder) ejecta-that, in part, they result from stochastic, inelastic collisions of ejecta and coalescence of partially-sintered agglomerates. The hypothesis is tested using direct observation of ejecta behavior, via high-speed imaging, to identify interactions between ejecta and consequences on melt pool formation. We show that stochastic collisions occur both between particles which are nearly-simultaneously expelled from the laser interaction zone and between particles ejected from distant locations. Ejecta are also shown to perturb melt pool geometry, which is argued to be a potential cause of lack-of-fusion flaws.

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