【作者】 顾小燕；

【导师】 李桓；

【作者基本信息】 天津大学 ， 材料加工工程， 2013， 博士

【摘要】 YAG激光+脉冲双电弧复合焊接是在激光焊与双丝焊的基础之上将复合焊的理念加以拓展，开发出的一种新型的焊接加工技术。目前，国内外对于复合焊的研究主要集中在激光与单电弧复合焊接方法的工艺研究与焊接过程模拟上，而对激光+双MIG/MAG复合焊接方法及其耦合机理本质的研究几乎没有。YAG激光+双MIG/MAG复合焊接过程中除了激光与电弧之间的耦合作用外，两个电弧之间也有复杂的交互作用，电弧之间的距离大小、焊枪夹角大小、电源供电模式的不同、激光作用点的改变等均会使整个焊接过程热场，力场，流场，电场，磁场以及三个热源之间的耦合机制发生变化，进而影响熔滴过渡、焊缝成形和微观组织。作为焊接加热的直接热源，激光复合电弧的性质对于整个焊接过程具有决定的意义，了解激光与双MIG/MAG电弧的相互作用方式与作用机理，对进一步的研究激光+双脉冲MIG/MAG复合焊接方法工艺具有指导性意义。本文系统地研究了Q235低碳钢YAG激光+脉冲双丝MIG复合焊接工艺特点及激光与双MIG电弧耦合机制。1.利用自行搭建的YAG激光+脉冲双丝MIG复合焊接系统，系统地研究了Q235低碳钢YAG激光+脉冲双丝MIG复合焊接工艺特点。试验结果表明：YAG激光的加入，改变了焊接熔池液态金属的流动方式。与双MIG电弧焊接相比，YAG激光+脉冲双丝MIG复合焊这种向熔池底部传热的熔池金属流动形式，有利于促使复合焊接熔池表面激光作用区域的高温、过热的液态金属向下运动，从而更多的热量被带到熔池底部而增加了焊接熔深。YAG激光+双MIG电弧复合焊接过程中，激光在工件表面作用区域由于金属蒸汽多、电子密度大而作为阴极斑点，稳定MIG电弧弧根，有效解决Q235低碳钢高速焊接时出现的咬边、断续等缺陷，获得连续、平滑的焊缝。Q235低碳钢YAG激光+双MIG电弧复合焊与双MIG焊焊缝组织对比发现，激光复合前后，焊缝区、熔合区以及热影响区的金相组织形态基本相同，只是YAG激光+双MIG电弧复合焊焊缝晶粒更为细小。2.利用光谱仪、采集卡和高速摄像机同步采集了YAG激光+脉冲双MIG电弧复合焊接过程中的电压、电流信号，光谱辐射信号，电弧形态以及熔滴过渡过程，结果表明：YAG激光的加入加速熔池表面金属蒸发电离，在熔池表面激光作用点附近形成包含大量导电粒子的电离通道，电弧被吸引至狭窄的电离通道处燃烧而导致弧柱横截面缩小。YAG激光的加入，能够降低MIG电弧电压，促进MIG电弧引弧，同时稳定电弧的阴极斑点，促进高速条件下电弧的稳定、规律燃烧，提高了复合焊接过程稳定性。激光应处于两个电弧之间，且与双个电弧之间的距离存在最佳范围值，在这个范围内两个电弧对激光的电磁作用力基本相等，激光等离子体内部的电子受到两侧电弧产生的洛伦兹力和电场力大致平衡，电子比较均匀地分布在等离子体中，此时，激光等离子体不发生偏移，两侧电弧稳定燃烧。间距过小或激光偏向其中一个电弧时，都会因为激光等离子体内部的平衡被破坏而导致的电弧阴极斑点的不稳定；而间距过大时，又会因为激光等离子体与电弧等离子体分离而失去复合的作用。在激光的热辐射、高温等离子体的反作用力、表面张力的改变的综合作用下，复合焊接的熔滴质量为双MIG焊的2倍左右，焊接熔滴过渡频率降低，与双MIG电弧焊相比，过渡频率降低10~20%。3.通过对YAG激光+双MIG电弧复合等离子体辐射强度、电子温度、电子密度空间分布的研究表明：激光复合后，没有新的线谱增加，但是光谱辐射强度明显大于双MIG焊，与双MIG焊接电弧相同区域相比，激光作用点上方复合焊接电弧弧柱区形成强烈收缩且该局部收缩区域的电子温度、电子密度升高，而远离复合焊电弧弧柱收缩区位置的差别不大，两个电弧等离子体被吸引靠拢到激光作用线附近，最高温度点也随之偏向激光作用线。激光作用线附近的电子温度随着双丝间距的减小及激光功率的增大而增加。YAG激光+双MIG复合等离子体符合局部热力学平衡条件。4.从非线性理论出发对YAG激光+双MIG电弧复合焊接电流的最大Lyapunov指数（LE）计算，结果表明：YAG激光+双MIG电弧复合焊接是一个复杂的混沌过程，LE的大小与焊接过程的稳定性有着紧密的联系，即焊接过程越稳定，最大LE值越小，其标准方差也越小。当处于最佳焊接规范时，最大LE最小。YAG激光+双MIG电弧复合焊接电流最大LE可以作为焊接过程稳定性的评价指标。更多还原

【Abstract】 YAG laser+pulse twin-MIG arc hybrid welding is a new joining technologybased on laser welding and tandem welding, which is the development of laser+archybrid welding. Currently, hybrid welding researches mainly focus on the applicationsof welding procedure and simulation of laser+single arc hybrid welding, but less onlaser+twin-arc hybrid welding.In addition to interactions of laser and arcs, there is also complex co-actionbetween the two arcs in YAG laser+pulse twin-MIG arc hybrid welding process. Asdirect heat sources, laser and arc have significance to welding process. Wire-wiredistance, angle between the wires, power supply mode and laser spot location all caninfluence thermal field, force field, magnetic field and coupling mechanism betweenthe heat sources, and then affect droplet transfer, weld appearance and microstructure.So sophisticated understanding of interactions between laser and arc can offerguidance for further practical research of YAG laser+pulse twin-MIG arc hybridwelding technology. In the paper, characteristic of welding technology and theinteraction mechanism between laser and arcs are investigated in the YAG laser+pulse twin-MIG arc hybrid welding of Q235mild steel.1. The welding technology of YAG laser+pulse twin-MIG arc hybrid welding isinvestigated using self-built welding system. The results indicate that: in YAG laser+pulse twin-MIG arc hybrid welding, flow mode of molten pool is altered after theinput of YAG laser, compared with twin-MIG welding, the flow mode of hybridmolten pool is helpful to force high-temperature liquid metal flow downward, andweld penetration increase accordingly. Because of much metal vapor and high densityelectron, laser spot location can offer a stable cathode spot for arcs. It is helpful toprevent the formation of undercut on the weld surface and make the weld formingcontinuous. The microstructure in weld center and heat affected zone produced byYAG laser+pulse twin-MIG arc hybrid welding is basically the same as that oftwin-arc welding. Proeutectoid ferrite along the grain boundary is less and smaller inhybrid welding.2. The arc behavior, droplet transfer, electrical signal and arc spectrum signal ofYAG laser+pulse twin-MIG arc hybrid welding process are recorded by high-speedcamera, DAQ card and spectrograph synchronously. The results indicate that thehybrid arcs are attracted to the laser-heated spot and the cross-section of hybrid arc column is constricted obviously. Voltage needed for arc ignition and combustiondecrease and stability of hybrid welding is prominent, especially in high-speedwelding. When laser-arc distance and arc-arc distance is optimal, electron in laserplasma is in equilibrium under the action of Lorentz force and electromagnetic force.Electrons evenly distributed at both side of the laser plasma to offer stable cathodespot. Internal equilibrium of laser plasma is broken because of short distance or laserdeviation, which lead to unstable of cathode spot. Laser plasma and arc plasmaseparate with each other and serve no purpose whatsoever in large distance. Droplettransfer frequency of hybrid welding reduces under the coactions of laser heat effect,reactive force offered by high temperature plasma and surface tension, which makesthe gravity of hybrid droplet is about2times than that of twin-arc droplet. Comparedwith twin-arc hybrid welding, droplet transfer frequency of hybrid welding decreasesby10~20%。3. Study on spatial distribution of radiation intensity, electron temperature anddensity of hybrid plasma indicate spectrum radiation, electron temperature and densitydistribution of hybrid plasma increase at the concentrated zone of hybrid arc columnbut there is no evident difference in the area far from concentrated zone. Electrontemperature near laser plasma increases with laser power but decreases with wire-wiredistance. Hybrid plasma of YAG laser+pulse twin-MIG arc hybrid welding is in alocal thermal equilibrium condition.4. Largest Lyapunov exponent (LLE) of current data in YAG laser+pulsetwin-MIG arc hybrid welding is calculated in term of non-linear theory. The resultsindicate YAG laser+pulse twin-MIG arc hybrid welding is a complex chaotic process.LLE is closely related to stability of welding process: the more stable the weldingprocess, the smaller LLE and its standard deviation. The smallest LLE can beacquired when welding technology is optimum. LLE can serve as evaluation index ofstability of.YAG laser+pulse twin-MIG arc hybrid welding process.更多还原