复杂金属构件激光选区熔化增材制造过程稳态堆积机制研究

The project will study on the accumulation layers’ perturbation, instability mechanism and stable growth control of complex metal components produced by selective laser melting，and focus on the interface reaction of the overlapped melting track, the cumulative effects of the fluctuating accumulation layers with perturbation conditions and self-adaptive adjusting mechanism. Based on the research of interfacial bonding between melting tracks of inner layer / between the layers to reveal overlapping mechanisms and build the mathematical model of overlapped tracks under ideal conditions. Based on morphology feature changes of accumulation layers to explore perturbation factors of the accumulation process and the corresponding perturbation mechanism, then acquire the cumulative law of fluctuating layers and its suppression methods, and explore the wetting, penetration and solidification behavior of liquid metal on accumulation layers when in stable and instable status respectively. On the basis of above research, perturbation factor would be introduced to establish a stable accumulation model under the perturbation process, then to find out the boundary conditions for the stable model and reduce its interference sensitivity. Finally, self-adaptive adjusting mechanism for fluctuations of accumulation layer will be revealed, thus a matching process for stable growth of accumulation layer will also be proposed. By studying the overlapping mechanism of melting tracks and perturbation mechanism and anti-interference ability during stable growth of accumulation layers, this project will give theoretical foundation for the realization of stable growth during Selective Laser Melting of complex metal components and expanding its applications in the high-tech field.

本项目针对复杂金属构件的激光选区熔化堆积层扰动/失稳机理及稳定生长控制展开研究，重点研究熔道搭接界面反应、工艺扰动条件下堆积层波动起伏累积效应及自适应调整机制等。基于层内/层间熔道界面结合规律研究以揭示堆积层搭接机制，并建立理想状态下熔道搭接的数学模型。基于堆积层形貌特征变化探索堆积过程的扰动因素及相应扰动机理， 进而获得堆积层波动起伏的累积规律及其抑制措施，并探索液相材料分别在堆积层稳定生长与非稳定生长时的润湿、渗透以及凝固行为。在此基础上引入扰动因子，建立工艺扰动条件下稳态堆积模型，获得堆积层稳定生长的边界条件，减少稳态堆积模型的抗干扰灵敏性。最终揭示堆积层波动起伏自适应调整机制，并由此提出堆积层稳定生长工艺匹配方法。本项目通过研究熔道搭接机制和堆积层稳定生长过程的扰动机理与抗干扰能力，为实现激光选区熔化成型过程稳定进行以及拓展激光选区熔化技术在高技术领域的应用奠定科学基础。

激光选区熔化成型工艺是多因素交互作用过程，导致了多层堆积过程复杂与不稳定且敏感，某个因素的微小扰动都有可能引发连锁效应，导致不稳定堆积在后续堆积层中累积发展，甚至使堆积层生长过程失稳。同时在某些情况下，堆积层生长的扰动在若干层后会自动消失，这说明多因素综合影响体系自身对于扰动具有一定的抵抗和消除能力。.一、主要研究内容.a.研究激光选区熔化成型的搭接机制及多层堆积演化行为；.b.研究堆积层非稳定生长过程的扰动因素及累积效应；.c.研究堆积层稳定生长机制并提出具有强抗干扰工艺匹配方法。.二、重要结果.a.建立并通过实验验证激光选区熔化零件表面粗糙度的理论模型；.b.从理论上解释了各典型几何特征的成型规律。通过优化悬垂结构的研究，提高悬垂面的成型质量。表面质量恶化后适时调整扫描速度，可以达到良好改善表面质量的效果；.c.针对激光选区熔化过程中不稳定因素飞溅的形成机理及对成型件微观组织和力学性能的影响进行讨论；.d.计算堆积层理论层厚h1，测量堆积层实际层厚h2，建立h1与h2与设定层厚h0的对应关系..三、关键数据.a.激光选区熔化过程中熔道之间的搭接率保证在30%左右，可以获得良好的搭接效果；.b.激光选区熔化上表面粗糙度理论计算值可以达到3-4微米之间;.c.飞溅粉末平均粒径为162μm，远大于原始粉末平均粒径32微米，且形貌多异，验证了SLM飞溅形成机理研究中的飞溅来源主要包括3类。飞溅粉末的主要组织成分与原始粉末基本一致，但其O、Si、C含量显著增高;.d.激光选区熔化实际层厚大于设定层厚，但加工一定层数后，实际层厚趋向稳定，大概等于设定层厚的2倍。.四、科学意义.项目研究激光选区熔化成型的失稳效应并在此基础上探索稳定堆积机理，采用理论与实验相结合的方法，围绕堆积过程中堆积层波动起伏产生与累积效应展开研究，建立三维实体生长稳态堆积模型和提出具有强抗干扰的工艺匹配方法，为堆积层稳定生长提供理论基础。