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

Abstract

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.

In-situ process monitoring and statistical quantification of powder bed forming and build processes in laser powder bed fusion additive manufacturing

“…Under the fabrication condition C, the depression and bulging areas are extremely close to the edge of the solidi ed part. The denudation area is formed by blowing powder near the edge of the part because the vapor plume is strongest at the edge as it serves as a turnaround position in the laser scan strategy [25].…”

“…However, these studies have focused on elucidating the mechanism underlying the occurrence of defects during laser radiation. In addition, there have been numerous studies on the spattering mechanism associated with the melt pool behavior [19][20][21][22][23][24][25]. As these studies investigated the single-track phenomena resulting from laser radiation, the practical melting phenomenon during the PBF-LB process was not considered comprehensively.…”

Advancements in 3D Printing: Directed Energy Deposition Techniques, Defect Analysis, and Quality Monitoring

“…Additionally, spatter occurs more frequently on the overhang structures [93]. The in situ monitoring system detected a considerable amount of heavy spattering at the contours [172]. On the built part side, a significant spatter was found, causing substantial disruption to the shape of the melt pool due to defects, such as balling caused by spatters and the separation of the melt.…”

Correlative spatter and vapour depression dynamics during laser powder bed fusion of an Al-Fe-Zr alloy

“…Reduced defects (or roughness) in the surface regions should bring further improvements on the fatigue performance of the LPBF components. These surface defects are often associated with spatter formation [1,[14][15][16][17][18][19] during LPBF and hence a better understanding of their evolution mechanisms is required to prevent them.…”

“…Four types of ejecta have been found in LPBF processes based on their formation mechanisms: (i) solid spatter, (ii) entrainment spatter, (iii) powder agglomeration, and (iv) liquid droplet spatter [20]. Solid spatter forms when powder particles are directly ejected by the high-pressure metallic vapour plume at the laser-matter interaction zone [16,21]. Entrainment spatter occurs when particles are entrained by a combination of inward shielding gas flow induced by the high-speed vapour plume and the wakefield generated by the scanning laser beam [22].…”