大尺寸多光束激光选区熔化的飞溅形成规律及控制方法研究

In order to meet the urgent needs of large-sized parts in aerospace, Selective Laser Melting (SLM) has been heading toward the large-sized multi-beam additive manufacturing. However, the number of spatters during multi-beam SLM processing is so large that it is difficult to remove, resulting in the increase of defects such as unfused defects, which may lead to the mechanical property being lower than that of single-beam SLMed parts. In addition, although the spatter generation mechanism of single-beam SLM has been attracted much attention, however, there are few reports regarding to the spatter generation of large-sized multi-beam SLM and its control methods. This project based on self-developed four-beam SLM equipment, using high temporal and spatial resolution, long-distance microscopy high-speed photography system combined with numerical simulation methods to study the pool characteristics and spatter generation under the multi-laser beam interaction, and its influence on the forming defects and its correlation with mechanical property. Furthermore, in order to obtain the control method during large-sized multi-beam SLM processing, the combination of optimized laser energy spatial distribution and powder bed preheating was used to study the spatter generation, and the optimized protective flow characteristics was adopted to remove the spatters. The research results contribute to a theoretical foundation for the realization of large-sized multi-beam SLM technology, which has theoretical significance and engineering value.

激光选区熔化（SLM）增材制造技术为满足航空航天等领域大尺寸精密零件成形的迫切需求，目前正朝着大尺寸多光束成形的方向迈进。但多光束SLM成形时飞溅数量多、难去除，致使未熔合等缺陷增多，导致其成形性能低于单光束SLM而形成瓶颈。此外，尽管单光束SLM飞溅形成规律及其危害已为人们所重视，但多光束SLM形成规律及其控制方法报道几为空白，亟待研究。本项目依托自主研发的四光束SLM成形装备，采用高时、空分辨特性的长距离显微高速摄影系统与数值模拟计算相结合等方法，研究多激光束交互作用下的熔池特征和飞溅形成规律，进而研究其对成形缺陷时空属性的影响及其与成形性能的内在联系；拟采用优化激光能量空间分布和粉末床预热相结合的方法，从源头抑制大尺寸多光束SLM成形飞溅，并通过优化保护气流特性来去除飞溅，以期获得大尺寸多光束SLM成形飞溅的控制方法。研究结果为实现大尺寸、多光束SLM技术革新奠定理论基础，具有十分重要的理论意义和工程价值。

激光选区熔化（SLM）正朝着多光束、大尺寸和高质高效方向迈进。然而，飞溅作为副产物，在多光束SLM成形条件下的飞溅形成机理尚未厘清，亟待研究。本项目依托多光束SLM设备和自主设计并搭建的高时空分辨原位成像系统，研究了多光束SLM成形中熔池特征和飞溅行为及对成形质量影响。主要研究成果如下：.① 率先探明了双光束激光与物质相互作用中飞溅主要形成机制的多重转变：从蒸汽反冲压和马兰戈尼效应诱导的熔池失稳为主导阶段，转变为蒸汽诱导的惰性气流卷吸作用为主导阶段，反之亦然。进而通过实验证实了多光束SLM飞溅数量增加的主因是蒸汽诱导的惰性气流卷吸作用，而不是主流观点认为的主要源于蒸汽反冲压。.② 探明了从熔池“液基”出射的熔滴飞溅的出射过程和熔体速度阈值，以及从基板“固基”出射的粉末飞溅的出射过程和气流速度阈值。金属蒸汽通过卷吸作用诱导的惰性卷吸气流，间接作用于粉末颗粒，形成粉末飞溅；金属蒸汽通过抬升力或反冲力，直接作用于粉末颗粒，使其进入蒸汽羽流或落回粉床。.③ 率先揭示了熔池飞溅行为与典型熔道“头凸尾凹”特征的内在关联，通过Langmuir方程和Miedema模型等热力学分析揭示了SLM成形中微爆炸的形成机理，进而探明了相变爆炸诱导飞溅与熔道缺陷相关性并提出了相关应对措施。研究结果不仅丰富了SLM激光与物质交互作用内涵，对理解掌握SLM缺陷形成机理有重要的理论意义和应用价值。.本项目发表学术论文10篇，5篇代表性论文SCI影响因子总和42.125（包括1篇Int. J. Mach. Tools Manuf.，3篇Addit. Manuf.和1篇金属学报），其中1篇入选ESI高被引论文，1篇入选中国精品科技期刊顶尖学术论文F5000；申请/授权国家发明专利4件；参加学术会议12人次，担任大会分会主席并做邀请/口头报告4人次，得到增材制造领域权威专家D. Bourell教授和J.P. Kruth教授积极评价，获RAAM2019国际学术会议最佳论文奖；担任SCI期刊Micromachines第一客座编辑；入选中国地质大学（武汉）“地大学者青年拔尖人才”1人，新聘教授和博士生导师1人；指导（含协助指导）研究生4人，博士后出站1人。