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 r_s, 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.

为满足航空航天和能源领域对大规模零件制造的迫切需求，激光粉末床融合（LPBF）增材制造正在向多激光粉末床融合（ML-PBF）方向发展。然而，在多束激光打印的沉积物的重叠区域更容易出现表面质量下降和未融合等缺陷，这不利于使用ML-PBF形成的零件的一致性和均匀性。在这里，基于高速、高分辨率成像技术和我们的 ML-PBF 设备，研究了 ML-PBF 重叠区域的双光束激光-物质相互作用。在重叠区域，两个熔池之间的碰撞和相互作用影响了液态金属的流动模式，伴随着大尺寸液滴飞溅的排出。而且，液态金属和飞溅物的碰撞和堆积是造成重叠样品表面和内部结构缺陷的原因。此外，我们揭示了 ML-PBF 中飞溅形成的主要机制的多种转变，可以从蒸汽诱导的反冲压力主导阶段转换为蒸汽诱导的夹带主导阶段。我们还提出了飞溅数的增长率r _s，它可以很好地与飞溅形成机制的瞬态转变相关。这项工作有望为 ML-PBF 实现一致性和统一性提供科学依据。