Melt pool stability criterion for beam shaping in laser-based powder bed fusion of metals

Laser-based powder bed fusion of metals (PBF-LB/M) is a well-established manufacturing technique that produces highly complex high-performance parts, typically in low volumes and at high costs per part. Expanding its market potential is directly linked to reducing costs per part. To address this, many companies and researchers are exploring beam shaping to enhance productivity and lower the cost per part. However, beam shaping introduces new challenges that must be addressed. This paper investigates the necessity of hatch spacing smaller than the beam diameter for shaped beams in PBF-LB/M. It introduces a newly observed process defect—bulging surfaces—previously identified in electron-beam-based powder bed fusion of metals (PBF-EB/M). The study explores the influence of line energy and hatch distance on melt pool stability and top surface roughness for Inconel 718 (IN718). The results show that top surface bulging becomes more pronounced with increasing hatch distance for constant line energies. A correlation is observed between newly introduced lateral velocity and melt pool stability, with higher lateral velocities leading to higher top surface roughness and reduced part density. The research highlights the importance of considering lateral velocity, influenced by scan vector length, hatch distance, and scan speed for large beam profiles (> 150 µm) in PBF-LB/M. This study contributes to a better understanding of process defects in PBF-LB/M using large and shaped beams.