Spattering mechanism of laser powder bed fusion additive manufacturing on heterogeneous surfaces

Laser powder additive manufacturing (PBF-LB) is an additive manufacturing method capable of producing high-precision and fully dense parts. However, nondestructively quality assurance of no internal defects remains challenging. Mitigating internal defects requires elucidating their formation mechanism and improving the PBF-LB process conditions. Therefore, we developed an in-situ monitoring system that combines surface morphology measurement by fringe projection and thermal field measurement with a high-speed camera. On heterogeneous surfaces in a practical multi-track PBF-LB process, a roughness index of the built part surface altered cyclically, consistent with the change in the angle between laser scanning and atmospheric gas flow. The high-speed camera monitoring showed that the melt pool was asymmetrical and spindle-shaped and that spatter was emitted mainly from the built part side of the melt pool. Furthermore, it was found that the built-part surface morphology under the powder layer affected the stability of the melt pool. As a result, a graphical representation of the melt pool and spattering for heterogeneous surfaces was proposed. Although it is still difficult to theoretically estimate the process window in which no spattering and no internal defects, in-situ monitoring equipment will provide knowledge to elucidate spattering and internal defects formation.