中空激光光内复合送料熔覆光/粉/丝耦合、熔凝及成形基础研究

Based on the hollow laser exchange by dual cone-cirque reflector mirrors, the laser cladding method of combining coaxial powder and wire feeding is applied to develop a new direct metal deposition technique. Its main characteristics is that the solid laser beam is transformed into the hollow laser beam and the powder wrapping the wire are delivered to the molten pool together from the inside of hollow laser beam. This new technique doesn't only combine the advantages of individual powder and wire feeding, but also overcomes their issues. What's more, it also improves the heat absorption rate, the penetration bead quality and forming efficiency, and controls the material gradient. In this study, the law , mechanism and effects of interactions among laser beam, powder and wire will be discussed, including the outside powder shielding effects to wire, the heat absorption and heat transfer of powder and wire to the laser beam, and the "heat island effect" of the wire. It will also be studied that the effect of saddle energy distribution of hollow laser to the mechanisms of the melting-solidification of powder and wire, the surface morphology and the fusion quality of the clad boundary, and physical 3-dimensional prototyping using powder-wire compound material. By adjusting the powder and wire flow field, the material gradient and its coupling mechanism with laser beam are designed to be controlled and researched. Numerical models of the thermal field, flow field and solidification stress field among powder, wire and laser beam will be established. This study will refine the research theory of material feeding by hollow laser beam and provides a new process and theoretical base for metal rapid deposition, especially for producing large dense metal components with high performance.

基于中空激光变换，提出"粉裹丝"激光光内同轴复合送料金属熔覆成形新方法，兼具送粉熔覆柔性好、吸热快、熔道平整、堆高性好和送丝熔覆选材范围广、材料利用率高、成本低的优势，并可实现梯度制造。拟深入探讨中空激光束对 "粉裹丝"复合体相互作用的规律、机制和效应，粉末对光反射的屏蔽作用，粉末与丝材的吸能、传热规律，中心丝材的"热岛效应"；研究中空激光特有的"光鞍"效应对于粉/丝二体共熔-凝固的机制与影响因素、熔道表界面构形与边界热熔合机理，以及粉/丝复合材料三维成形机制；通过调节粉、丝流场控制材料成分，深入研究粉、丝流渐变与激光耦合的演变机制，获得梯度成形实体；建立激光光内复合送料光/粉/丝耦合温度场、流场及凝固应力场模型。本研究为激光熔覆增材制造，特别是大型、高性能致密金属零件或梯度功能件的直接成形提供新方法、新理论和新技术。

项目发明了包围光束送粉/丝激光熔覆喷头，具有材料与三光束同轴并垂直于基体表面,成形无扫描方向性影响；中心送丝/粉受热均匀，熔池对流传热传质均匀，熔覆层质量提高；光、丝/粉精确耦合，避免光料干涉，激光能量利用率高；送丝/粉通道空间不受光束的影响，送丝/粉速度的稳定等优势。同轴送丝、送粉复合喷嘴及其调节装置，实现金属丝、金属粉末、激光束、保护气气帘同轴和精确耦合。项目探讨了中空激光束对粉/丝及其复合作用的规律、机制和效应，研究了粉末浓度分布及其对光吸收作用，粉末与丝材的吸能、传热规律。探索了中空激光特有的“光鞍”效应对于粉/丝熔化-凝固机制与影响因素、熔道表面形貌与边界热熔合机理，以及粉/丝复合材料三维成形机制。对空间熔池截面形貌进行了力学分析，建立了熔池的形貌、受力与静态、动态运动模型。斜面熔池在重力影响下发生位移后，金属液体的表面张力是阻止熔池位移的主要因素。可通过控制熔池高度、宽度、基体倾斜角度、熔池温度等参数来改变熔池的受力状态，从而抑制熔池的位移和流淌，提高堆积形貌精度和成形稳定性。通过调节粉、丝流场控制材料成分，深入研究了粉、丝流渐变与激光耦合的演变机制，建立了激光光内复合送料光/粉/丝耦合温度场、流场及凝固应力场模型。项目获得了光内送粉/丝熔覆成形装置，并获得成形样件。