Heat and mass transfer in spatially oscillating laser powder bed fusion

Spatially oscillating laser powder bed fusion (SO-LPBF) presents an attractive approach to dynamic beam shaping, fundamentally altering what is possible in terms of heat and mass transfer during laser-based metal 3D printing. This study offers a systematic process characterisation of SO-LPBF, employing in-situ multimodal imaging to capture detailed melt pool and spatter dynamics. Ex-situ profilometry, metallurgical characterisation and EBSD analysis show the effect of beam stirring on the deposited bead geometries and microstructures. We develop comprehensive process maps by correlating our observations with dimensionless parameters, effective fluence metrics, and semi-analytical modelling. Our findings reveal that properly tuned oscillation parameters create a "thermal reservoir" effect, enhancing melt pool stability and suggesting the potential of processing thicker powder layers. This leads to a potential doubling of productivity with existing technology and lays the groundwork for further scaling. The detailed insights and scaling guidelines presented here serve as a valuable resource for optimising SO-LPBF, advancing it as a highly efficient and versatile additive manufacturing technique.