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

Area of Science:

• Materials Science
• Manufacturing Engineering
• Physics of Additive Manufacturing

Background:

• Large ejecta, exceeding feedstock powder size, are observed in powder bed fusion (PBF) additive manufacturing (AM).
• The origin of these oversized ejecta remains inadequately explained, posing challenges for process control and part quality.
• Understanding ejecta formation is crucial for improving the reliability of PBF processes.

Purpose of the Study:

• To investigate the hypothesis that large ejecta originate from stochastic collisions and coalescence of partially-sintered agglomerates.
• To directly observe ejecta behavior and its impact on the melt pool during PBF.
• To identify the mechanisms contributing to the formation of oversized particles in the PBF process.

Main Methods:

• High-speed imaging was employed to capture direct observations of ejecta dynamics.
• Analysis focused on identifying interactions between ejecta particles and their effect on melt pool geometry.
• Experimental conditions were set to mimic typical powder bed fusion additive manufacturing scenarios.

Main Results:

• Stochastic collisions between ejecta particles were confirmed, occurring both from simultaneous and spatially separated ejections.
• Partially-sintered agglomerates were observed to coalesce, contributing to larger particle sizes.
• Ejecta were shown to significantly perturb the melt pool's geometry during the process.

Conclusions:

• The study provides evidence supporting the hypothesis that particle collisions and agglomeration contribute to large ejecta formation in PBF.
• Observed melt pool perturbations by ejecta are a potential cause of lack-of-fusion defects in additive manufactured components.
• Further research into controlling ejecta dynamics could enhance the quality and consistency of PBF parts.