Laser powder bed fusion in high-pressure atmospheres
High-speed imaging and schlieren imaging were used to investigate the interaction of the laser beam with the powder bed at pressures up to 5 bar, in argon and helium atmospheres. The entrainment of powder particles in the flow of shielding gas generated by the laser plume, and hence denudation, was reduced at high pressure for both gases. However, for argon, high pressure increased the temperature of both the melt pool and the laser plume, which significantly increased the generation of spatter and ionisation of the metal vapour with degraded surface smoothness and continuity. For helium, the formation of spatter and plasma did not increase with the increase in pressure above that observed at atmospheric pressure: its higher thermal conductivity and thermal diffusivity limited the laser plume temperature. Layers built at 5 bar in helium had a surface smoothness and continuity comparable to those built in argon at atmospheric pressure, but achieved at a higher laser scan speed, suggesting that a high-pressure helium atmosphere may be used to enhance the build rate.
KeywordsHigh-speed imaging Laser powder bed fusion High pressure atmosphere Argon atmosphere Helium atmosphere
The authors are grateful to Jolyon Cleaves of Vision Research for use of the Phantom V2512 high-speed camera, and to Toby Scrivener of Laser 2000 (UK) Ltd. for use of the Lumencor SOLA SM light engine.
This work was supported by the Engineering and Physical Sciences Research Council (Grant number EP/K030884/1).
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