Dual-beam laser-matter interaction at overlap region during multi-laser powder bed fusion manufacturing

Abstract To meet the urgent demand of large-scale parts fabrication in aerospace and energy fields, laser powder bed fusion (LPBF) additive manufacturing is developing towards multi-laser powder bed fusion (ML-PBF). However, defects such as the surface quality degradation and lack of fusion are more prone to appear at the overlap region of the deposit printed by multiple laser beams, which is detrimental to the consistency and uniformity of parts formed using ML-PBF. Here, based on a high-speed, high-resolution imaging technology and our ML-PBF equipment, the dual-beam laser-matter interaction at the overlap region in ML-PBF was investigated. At the overlap region, the collision and interaction between two molten pools influences the flow pattern of the liquid metal, accompanied by the large-sized droplet spatter expelling out. Moreover, the collision and accumulation of the liquid metal and spatter are responsible for the formation of the surface and internal structure defects of overlap samples. Furthermore, we reveal multiple transitions of the dominant mechanisms of the spatter formation in ML-PBF, which can be interchanged from the vapor-induced recoil pressure dominant stage to the vapor-induced entrainment dominant stage. We also propose the growth rate of spatter number rs, which can be well correlated with the transient transition of spatter formation mechanism. This work is expected to provide the scientific basis for ML-PBF to achieve consistency and uniformity.