【作者】 高明；

【导师】 曾晓雁； 胡乾午；

【作者基本信息】 华中科技大学 ， 物理电子学， 2007， 博士

【摘要】 激光-电弧复合焊接技术是一种将激光束与电弧集成于一体的新型焊接技术,能够弥补单热源焊接的不足,具有焊接熔深大、工艺稳定性好、焊接速度快、变形小、间隙桥接能力强等优点。近年来,该技术在发达国家受到了广泛关注并得到了积极的研究,在汽车、石油、船舶、压力容器等领域极富发展前景。但是,由于种种原因,可获取的关键技术信息比较匮乏,有关激光-电弧两种热源之间相互作用机理的研究也非常有限,缺乏系统深入的研究。因此,迫切需要从基础的科学问题入手,推动激光-电弧复合焊接技术的发展。本文采用低碳钢和不锈钢材料从基础工艺、保护气体、热源相互作用机理、接头微观组织和力学性能等方面入手,对CO2激光-TIG (tungsten inert gas)和MIG (metal inert gas)电弧复合焊接技术的工艺和机理进行了系统深入的研究。主要研究成果如下:构建了一个由CO2激光器、TIG和MIG焊机、数控工作台组成的激光-电弧复合焊接系统,能够方便的调节各焊接参数,并实现激光与电弧的协同效应。在该平台上分别进行了激光-TIG和MIG电弧复合焊接的基础工艺研究,并得到了优化的工艺参数范围。试验发现:激光和电弧能够通过形成于激光光致等离子体和电弧之间的导电通道发生强烈的相互作用。同激光焊接相比,激光-MIG电弧复合焊接熔深提高60%,焊接速度提高170%;激光-TIG电弧复合焊接熔深提高44%。系统研究了激光-电弧复合焊接中气体保护方式及成分组成的影响规律。研究证明电弧焊炬加同轴喷嘴的气体保护方式是激光-电弧复合焊接的最佳气体保护方式;He-Ar混合气体更适用于激光-电弧复合焊接。保护气体通过激光与电弧等离子体相互作用、气流方向与速度变化来改变等离子体形态(等离子体有效作用高度)是改变复合焊接熔深和工艺稳定性的关键作用机制。首次提出了更全面的激光-电弧复合焊接热源相互作用定量分析方法。引入了无量纲参数——复合焊接熔化能增量ψ来表征热源相互作用:ψ值越大,热源相互作用越强烈。定量分析结果和试验现象能够很好的吻合,表明该方法能够快速准确的全面反映激光、电弧之间的热源相互作用。采用该方法进行热源相互作用定量分析发现:对应不同类型的电弧,激光-电弧复合焊接的热源相互作用程度存在差异。该差异来自于电弧电极极性对激光光致等离子体的影响及其自身特性的不同。发现激光-MIG电弧复合焊接接头内电弧区焊缝组织为垂直于熔池壁向中心生长的粗大的带状树枝晶;激光区焊缝组织为靠近熔池壁垂直于熔池壁生长的柱状树枝晶和中心区域均匀形核的细小等轴树枝晶,且激光区具有更高的焊缝显微硬度和更窄的热影响区,国内外未见有类似报道。得到了激光-电弧能量配比、坡口形式、保护气体等焊接参数对接头力学性能和微观组织的影响规律,对工艺参数的选取有一定的理论指导意义。开展了超细晶粒钢的激光-TIG复合焊接研究。试验证明超细晶粒钢的激光-TIG复合焊接接头强度高于母材,焊缝区显微硬度低于激光焊接,能够避免因显微硬度过高造成的韧性下降,有效抑制热影响区晶粒长大倾向并避免软化区的出现,并提高焊接速度。结果表明该技术在超细晶粒钢的焊接中具有很大的应用前景。系统研究了激光-MIG电弧复合焊接的焊缝缺陷、焊接适应性及临界焊接速度。通过试验得到了临界咬边速度经验公式、焊缝缺陷抑制方法、接头间隙桥接极限及可焊错边量极限,并得到了激光-MIG电弧复合焊接的临界速度变化规律。在此基础上,总结出一套可得到稳定工艺过程和良好焊缝质量的复合焊接质量控制方案,有利于发展具备自主知识产权的复合焊接工艺和成套设备。更多还原

【Abstract】 Laser-arc hybrid welding which couples laser beam and arc into one process avoids the disadvantages of individual process and has its own particular advantages, such as deeper welding penetration, more stable welding arc, higher welding speed, less deformability and stronger ability to bridge large gaps, etc. For these advantages, the laser-arc hybrid welding technologies have become more and more attractive in recent years and have strong industrial application prospect in many fields, such as aerospace, automotive, off-road vehicle, shipbuilding, oil and pressure vessel industries, etc. However the researches on this process are very scattered and the useful information is relatively scarce. The studies on laser-arc interaction mechanism are also very few, and further systemic investigations are needed.In this dissertation, the basic processing which considers different processing parameters such as shielding gas, laser-arc interaction, weld microstructure and mechanical performance with the CO2 laser-TIG (tungsten inert gas) and MIG (metal inert gas) hybrid welding are studied in detail by the use of the mild steel and stainless steel,. The following are the main results:A system of laser-arc hybrid welding was developed, which include a CO2 laser, a TIG and a MIG arc welder and CNC controller, etc. Some parts were also optimized to fit the process. Using this system, the welding parameters can be adjusted conveniently and the laser-arc synergetic effects can be obtained. Both the laser-TIG and laser-MIG hybrid welding were investigated in detail and the optimal parameter range was obtained. The experimental results demonstrate that there exists strong laser-arc interaction through the electrical channel between laser induced plasma and arc column observed in the experiment. Compared to the individual laser welding, the weld penetration depth and the welding speed of laser-MIG hybrid welding increase by 1.6 and 2.7 times respectively, and the weld penetration depth of laser-TIG hybrid welding also increases by 1.44 times.The shielding gas parameters of laser-arc hybrid welding were studied systemically, which demonstrate the evident effects of shielding gas parameters on the weld penetration depth. It was found that the optimal gas shielding method is the hybrid protecting method coupling the torch and coaxial nozzle, which can achieve efficient synergetic effects and produce the full penetration weld under the considerably wide parameter range. It is also testified that the mixed gas of helium and argon is more suitable for laser-arc hybrid welding. The shielding gas parameters affect the weld penetration and the process stability by influencing the plasma shape (efficient plasma height interacting with laser), which is achieved by two ways: laser-arc plasma interaction and gas flowing direction and velocity.A more comprehensive quantitative analysis method was originally developed firstly to study the heat sources interaction extent between the laser and arc during the hybrid welding process. A dimensionless parameter,ψ, was introduced to indicate the changes of heat sources interaction: the biggerψdenotes the stronger heat sources interaction. The agreement of the computed results by this method with the phenomenon observed in hybrid welding indicates this method can comprehensively reflect the laser-arc interaction of hybrid welding fast and accurately. By this method, it can be observed that, for different arc type, a significant difference of the heat sources of laser-arc hybrid welding from the analytical results. This difference is mainly caused by the effect of electrode polarity on the characteristic of laser induced plasma and the difference of arc characteristic.It was found by the microscopic observations that in the weld region of laser-MIG hybrid welded mild steel, the microstructure of the arc zone is coarse columnar dendrite perpendicularly growing from the melting pool wall to the center; that of laser zone is relatively fine columnar dendrites perpendicularly growing from the melting pool wall to the center and fine equiaxed dendrite homogeneously nucleating in the center zone, which was not reported eslswhere. The aser zone has higher microhardness of the weld region and narrower heat affected zone. Moreover, the effects of laser-arc energy ratio, groove type and shielding gas on the microstructure and mechanical performance of the weld produced by hybrid welding are obtained by experiments, which is instructive for the choose of welding parameters.Laser-TIG hybrid welding was used to weld superfine grain steel in this dissertation. The experiments showed that the joint strength of laser-TIG hybrid welded superfine grain steel is higher than that of base metal, and the microhardness is also lower than that of laser welded one, which can avoids the decrease of the weld toughness resulting from the overhigh microhardness in the weld region. Moreover, laser-TIG hybrid welding can obtain narrower HAZ to restrain the grain coarsening and avoid the appearance of softened one because of the higher speed. These indicate the great prospect of hybrid welding for superfine grain steel.Finally the weld defects, welding adaptability and critical welding speed of laser-arc hybrid welding were investigated in detail. Many useful conclusions, such as the experiential formula of critical undercut speed, some methods for restraining weld defects, the limit of gap bridging and weldable misalignment, and the range of critical welding speed were firstly obtained. Based on the experimental results and discussions, a scheme for choosing the best hybrid processing parameters to control the bead quality was developed firstly, which is highly helpful to the equipment developing of laser-arc hybrid welding.更多还原