基于光内送粉激光熔覆扭曲薄壁件的成形研究
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摘要
激光熔覆成形技术LCRM（Laser Cladding Rapid Manufacturing）是20世纪90年代中后期发展起来的一种先进制造技术，它综合了激光熔覆技术与快速成形技术的优点，在汽车、钢铁、航空、航天、电子等方面都有广泛应用。目前此项技术中成形所采用送粉方式多为光外侧向同轴送粉，该种方式激光束与粉末耦合性差，成形件表面较粗糙，金属粉末利用率低。本实验室提出一种新的光内送粉激光熔覆成形技术，具有光粉耦合好，粉末利用率高，熔道平整等优点。本文重点对光内送粉激光熔覆熔池温度场以及熔覆成形扭曲薄壁高层零件进行研究。
设计了一种新型光内泄压送粉喷嘴。在原有环形光光内送粉激光熔覆成形光头的基础上，对送粉喷嘴进行了改进，设计了一种泄压送粉喷嘴，送粉效果显示泄压后的粉末束在保护气体的约束下汇聚的更细，直线段距离更长，可进一步提高粉末利用率，同时有助于薄壁件的熔覆成形。
分析了光内送粉单道激光熔覆的温度场。理论分析了环形光辐照下扫描线宽方向吸收能量的“马鞍形”分布，建立了环形光光内送粉单道激光熔覆的有限元模型，得到了单道熔覆过程中熔池的温度场分布呈彗星状，高温区域形状似“马鞍形”；提出了通过观察熔池横断面温度分布等值线图来判断熔覆层成形质量和其与基体的结合情况，且单道实验验证了其准确性；另外熔池中心的定点在环形光扫过时经历了两次升温和降温的过程，熔池近边缘和熔池中心的点在光斑扫过的时候温差不大，说明了环形光光内送粉激光熔覆的优越性。
系统研究了激光功率、送粉速率、扫描速度和离焦量等因素对激光熔覆成形单道熔覆层表面形貌以及熔覆层高度和宽度的影响。研究得出了一些重要结论，为采用该工艺成形薄壁扭曲零件以及今后环形光光内送粉激光熔覆成形技术的应用提供重要参考和依据。
试验堆积成形了扭曲薄壁件。在单道实验的基础上确定了扭曲薄壁件光内送粉激光熔覆成形的初始参数和试验方案；建立了扭曲薄壁件激光熔覆成形的有限元模型，分析了扭曲薄壁件熔覆成形过程中温度场的演变过程和定点温度的热循环，并且通过仿真实时控制模型中输入激光功率的大小，模拟得到了保持熔池温度稳定时激光功率的变化值；通过层高控制和参照数值计算得到的功率变化值调节激光器功率，成功熔覆成形了扭曲薄壁件，性能分析表明：成形件表面光滑，没有粘粉，尺寸与设计数值基本相同，组织细小致密，与基体形成冶金结合，且成形件硬度较高。
LCRM is an advanced manufacturing technology developed from the1990s, itcombines the advantages of the laser cladding and the rapid forming technique, and isused widely in the car, steel, aviation, aerospace, and electronics industry. At present, inthis technology, the powder feeding way of forming is lateral coaxial powder feedingoutside the laser beam, in this way, laser beam and powder couples badly, theaccumulated parts have rough surfaces, and the utilization of metal powder is low.Soochow university laser special processing lab put forward a new laser claddingmanufacturing process with coaxial inside-beam powder feeding, it can make the laserbeam and the powder couple well, and improve the utilization rate of powder, also canmake the cladding layer more flat. In this paper, the temperature field of laser claddingand the forming process of screwy thin-walled part will be researched.
In order to cover the shortage of the present powder feeding nozzle, this paper hasdesigned a pressure relief powder feeding nozzle base on coaxial inside-beam powderfeeding laser head, powder feeding effect shows that powder bunch become moreslender and straight under the restriction of the protection gas, it can improve thepowder utilization and be useful for the thin-walled parts laser cladding forming.
The saddle distribution of energy absorbed at scanning direction is researched.Through building the finite element model of coaxial inside-beam powder feeding lasercladding, molten pool temperature field of single laser cladding is got, it is like a comet,and the high temperature area is like a saddle. The conclusion that the combinationbetween cladding layer and substrate can be judged by observed the molten poolcross-sectional temperature distribution isoline, and it is test by single laser claddingexperiments. The nodes in the middle of molten pool undergo warming and coolingtwice when the ring laser scanning across them. The temperature difference between molten middle and edge isn't big, and it reflects the superiority of inside-beam powderfeeding laser cladding.
The effects of laser power, powder feeding rate, scanning speed, anddefocusingamount to single cladding layer surface, height, and width are studiedscientifically. Some conclusions are obtained, and these can be the references for usingthis technology forming thin-walled screwy part and the application of inside-beampowder feeding laser cladding forming.
Base on the single laser cladding experiments, screwy thin-walled part inside-beampowder feeding laser cladding forming initial parameters and test plans are confirmed.The finite element model of laser cladding forming screwy thin-walled part isestablished. The evolution of temperature field and thermal cycle of the node are studiedduring the screwy thin-walled part forming process. In the emulation laser power ischanged real time, and it can keep the molten pool temperature steady. The screwythin-walled part is formed successfully through storey height control and laser powerchange real time. Performance analysis shows that formed part has smooth surface and ahigh rigidity, no powder paste outside the surface, the size is basically the same to thedesign value, the microstructure is small and density, metallurgical combination isformed between part and substrate.
设计了一种新型光内泄压送粉喷嘴。在原有环形光光内送粉激光熔覆成形光头的基础上，对送粉喷嘴进行了改进，设计了一种泄压送粉喷嘴，送粉效果显示泄压后的粉末束在保护气体的约束下汇聚的更细，直线段距离更长，可进一步提高粉末利用率，同时有助于薄壁件的熔覆成形。
分析了光内送粉单道激光熔覆的温度场。理论分析了环形光辐照下扫描线宽方向吸收能量的“马鞍形”分布，建立了环形光光内送粉单道激光熔覆的有限元模型，得到了单道熔覆过程中熔池的温度场分布呈彗星状，高温区域形状似“马鞍形”；提出了通过观察熔池横断面温度分布等值线图来判断熔覆层成形质量和其与基体的结合情况，且单道实验验证了其准确性；另外熔池中心的定点在环形光扫过时经历了两次升温和降温的过程，熔池近边缘和熔池中心的点在光斑扫过的时候温差不大，说明了环形光光内送粉激光熔覆的优越性。
系统研究了激光功率、送粉速率、扫描速度和离焦量等因素对激光熔覆成形单道熔覆层表面形貌以及熔覆层高度和宽度的影响。研究得出了一些重要结论，为采用该工艺成形薄壁扭曲零件以及今后环形光光内送粉激光熔覆成形技术的应用提供重要参考和依据。
试验堆积成形了扭曲薄壁件。在单道实验的基础上确定了扭曲薄壁件光内送粉激光熔覆成形的初始参数和试验方案；建立了扭曲薄壁件激光熔覆成形的有限元模型，分析了扭曲薄壁件熔覆成形过程中温度场的演变过程和定点温度的热循环，并且通过仿真实时控制模型中输入激光功率的大小，模拟得到了保持熔池温度稳定时激光功率的变化值；通过层高控制和参照数值计算得到的功率变化值调节激光器功率，成功熔覆成形了扭曲薄壁件，性能分析表明：成形件表面光滑，没有粘粉，尺寸与设计数值基本相同，组织细小致密，与基体形成冶金结合，且成形件硬度较高。
LCRM is an advanced manufacturing technology developed from the1990s, itcombines the advantages of the laser cladding and the rapid forming technique, and isused widely in the car, steel, aviation, aerospace, and electronics industry. At present, inthis technology, the powder feeding way of forming is lateral coaxial powder feedingoutside the laser beam, in this way, laser beam and powder couples badly, theaccumulated parts have rough surfaces, and the utilization of metal powder is low.Soochow university laser special processing lab put forward a new laser claddingmanufacturing process with coaxial inside-beam powder feeding, it can make the laserbeam and the powder couple well, and improve the utilization rate of powder, also canmake the cladding layer more flat. In this paper, the temperature field of laser claddingand the forming process of screwy thin-walled part will be researched.
In order to cover the shortage of the present powder feeding nozzle, this paper hasdesigned a pressure relief powder feeding nozzle base on coaxial inside-beam powderfeeding laser head, powder feeding effect shows that powder bunch become moreslender and straight under the restriction of the protection gas, it can improve thepowder utilization and be useful for the thin-walled parts laser cladding forming.
The saddle distribution of energy absorbed at scanning direction is researched.Through building the finite element model of coaxial inside-beam powder feeding lasercladding, molten pool temperature field of single laser cladding is got, it is like a comet,and the high temperature area is like a saddle. The conclusion that the combinationbetween cladding layer and substrate can be judged by observed the molten poolcross-sectional temperature distribution isoline, and it is test by single laser claddingexperiments. The nodes in the middle of molten pool undergo warming and coolingtwice when the ring laser scanning across them. The temperature difference between molten middle and edge isn't big, and it reflects the superiority of inside-beam powderfeeding laser cladding.
The effects of laser power, powder feeding rate, scanning speed, anddefocusingamount to single cladding layer surface, height, and width are studiedscientifically. Some conclusions are obtained, and these can be the references for usingthis technology forming thin-walled screwy part and the application of inside-beampowder feeding laser cladding forming.
Base on the single laser cladding experiments, screwy thin-walled part inside-beampowder feeding laser cladding forming initial parameters and test plans are confirmed.The finite element model of laser cladding forming screwy thin-walled part isestablished. The evolution of temperature field and thermal cycle of the node are studiedduring the screwy thin-walled part forming process. In the emulation laser power ischanged real time, and it can keep the molten pool temperature steady. The screwythin-walled part is formed successfully through storey height control and laser powerchange real time. Performance analysis shows that formed part has smooth surface and ahigh rigidity, no powder paste outside the surface, the size is basically the same to thedesign value, the microstructure is small and density, metallurgical combination isformed between part and substrate.
引文
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