The interplay between vapour, liquid, and solid phases in laser powder bed fusion

The capability of producing complex, high performance metal parts on demand has established laser powder bed fusion (LPBF) as a promising additive manufacturing technology, yet deeper understanding of the laser-material interaction is crucial to exploit the potential of the process. By simultaneous in-situ synchrotron x-ray and schlieren imaging, we probe directly the interconnected fluid dynamics of the vapour jet formed by the laser and the depression it produces in the melt pool. The combined imaging shows the formation of a stable plume over stable surface depressions, which becomes chaotic following transition to a full keyhole. We quantify process instability across several parameter sets by analysing keyhole and plume morphologies, and identify a previously unreported threshold of the energy input required for stable line scans. The effect of the powder layer and its impact on process stability is explored. These high-speed visualisations of the fluid mechanics governing LPBF enable us to identify unfavourable process dynamics associated with unwanted porosity, aiding the design of process windows at higher power and speed, and providing the potential for in-process monitoring of process stability. Complexities of laser-material interactions pose a challenge to minimize defects in additively manufactured metal parts. Here the authors visualize all phases of matter simultaneously to expand understanding of the interactions and show atmospheric information can characterize process stability.

Automated summary

In this study, the authors directly investigated the impact of laser-material interaction on laser powder bed fusion (LPBF) process using simultaneous in-situ synchrotron x-ray and schlieren imaging. By quantifying the morphological changes during the process, the instability of the process was revealed, and the effect of the powder layer on process stability was explored. These findings contribute to the design of process windows at higher power and speed, and provide a potential method for monitoring process stability.