【作者】 郝新锋；

【导师】 刘黎明；

【作者基本信息】 大连理工大学 ， 材料加工， 2010， 博士

【摘要】 激光+电弧复合热源焊接技术作为一种新型、高效的焊接技术,以其焊接熔深大、焊接速度快、变形小、搭桥能力强等优点,受到国内外学者的广泛关注。近年来,随着激光器的发展,大功率激光器越来越多地应用于复合焊接技术,目前激光+TIG电弧复合焊接技术研究主要采用几千瓦甚至几十千瓦的大功率激光与电弧进行复合,以大功率激光为主,TIG电弧为辅。但是激光器电-光转换效率普遍较低,同时电弧对激光具有吸收和散焦作用,并随着激光功率的增大而增强,导致激光能量利用率降低,因此,大功率激光的应用必然导致能源的大量消耗及浪费。基于我国激光器发展现状,开发焊接效率高、能源消耗少、具有自主知识产权的低功率YAG激光+TIG电弧复合焊接技术具有重要的现实意义,有利于推动复合焊接技术在生产中的应用和发展。因此,本文采用低功率YAG激光(小于500W)与TIG电弧复合,系统地研究了低功率YAG激光+TIG电弧复合焊接工艺特点,开发了低功率YAG激光+TIG复合热源填丝焊接技术；分析了复合焊接过程中的电弧等离子体形态及光谱信息的变化,深入探讨了低功率YAG激光与TIG电弧的相互作用机理;并在此基础上,对低功率YAG激光+TIG电弧复合焊接过程中激光脉冲与交流电弧的相位匹配进行控制,进一步改善复合焊接效果。本文主要研究内容：1.系统地研究了低功率YAG激光+TIG电弧复合焊接(未填丝及填丝)工艺特点,得到了镁合金、钛合金薄板结构件的焊接参数范围。结果表明,低功率YAG激光+TIG电弧复合焊接焊缝成形良好,单面焊双面成形,焊接速度相比TIG焊接成倍提高；焊丝的加入避免了焊缝塌陷、咬边等缺陷的产生,后送丝方式下复合填丝焊接熔深达到前送丝复合填丝焊接的2倍左右,焊接接头热影响区窄,晶粒长大不明显,接头拉伸性能达到母材的95%左右。复合热源填丝焊接技术为低功率YAG激光+TIG电弧复合焊接中厚板材提供了可行性。2.采集焊接过程中等离子体形态及等离子体光谱信息,系统研究了低功率YAG激光对焊接等离子体的影响。结果表明：激光加入后,镁合金大量蒸发、电离,焊接等离子体的亮度急剧增强,体积发生膨胀,激光作用在电弧负半波时显著提高电弧等离子体的稳定性。焊接等离子体光谱表明,激光焊接等离子体光谱只有少量的Mg原子线状谱,并且强度比较低；TIG焊接和复合焊接等离子体光谱主要由Mg I谱线,MgΠ谱线,ArI谱线和ArΠ谱线组成,激光加入后,Mg元素谱线强度增强,而Ar元素谱线强度降低；利用Mg I谱线计算等离子体的电子温度和电子密度,结果表明：激光加入后电弧等离子体电子温度降低,电子密度提高；焊丝的加入使填丝焊接过程中激光对电弧等离子体形态、等离子体电子温度和电子密度的影响不如未填丝焊接过程强烈；进一步实验发现未填丝焊接过程中激光增强TIG电弧等离子体的临界功率值为50-60W,填丝焊接过程为70W左右。3.通过分析焊缝成形特征、等离子体形态、光谱信息及电弧电压的变化,系统探讨了低功率YAG激光与TIG电弧等离子体之间的相互作用机制。结果表明：低功率YAG激光与TIG电弧的相互作用分为电弧对低功率YAG激光的辅助作用和YAG激光对电弧等离子体的增强作用两个方面。一方面,TIG电弧通过改变板材表面状态,使激光小孔的初始形成条件从“加热母材”阶段转变为“等离子体形成”阶段,促进了激光小孔的形成过程,同时电弧和保护气的作用使激光等离子体向后倾斜,减弱了激光等离子体对激光能量的吸收和散焦作用；另一方面,低功率YAG激光提高了TIG电弧的稳定性,并使电弧等离子体整体膨胀而高温导电通道收缩,引起电弧电压升高,导致电弧能量密度提高；两方面的综合作用使得复合热源焊接熔深显著提高。4.研究激光脉冲波形及脉冲激光与交流电弧的相位匹配对复合热源焊接质量的影响,设计激光脉冲与交流电弧的相位匹配控制系统,对复合焊接过程进行控制和改善。结果表明：在保持激光脉冲能量不变的前提下,在激光脉冲波形前部设置高功率密度的短时脉冲,适当延长激光脉冲脉宽,可以加快复合焊接过程中激光小孔的形成过程,增强激光对熔池的冲击作用,延长激光小孔对电弧等离子体的作用时间,有利于提高复合热源焊接熔深,熔深可提高15%-20%。脉冲激光与交流电弧相位匹配实验结果表明：无论脉冲激光作用于交流电弧正半波还是负半波,都能获得良好的复合焊接效果,但是复合焊接过程中激光小孔稳定电弧负半波有利于改善焊缝成形,同时由于电弧负半波对板材的输入功率相对较大,作用在激光小孔处的阴极斑点力比正半波时的阳极斑点力大,导致脉冲激光作用于电弧负半波时的焊接熔深相比作用于正半波提高5%-10%。更多还原

【Abstract】 As a new welding technique with high quality, laser+arc hybrid welding process has received significant attentions all over the world for its particular advantages, such as the large welding penetration, high welding speed, less deformations and good bridging ability for relatively large gaps, etc. In recent years, with the development of high-power laser apparatus, high-power laser beam are increasingly applied in hybrid welding applications, in which high-power laser plays the principal role with the assistance of arc. Due to the low electric-photo transformation efficiency of laser apparatus and the absorption and defocusing effects of arc plasma on laser beam, which intensifies with the increase of laser power, the utilization ratio of laser energy decreases significantly. Therefore, the applications of high-power laser beam will induce serious waste of energy. Based on the development status of laser apparatus in our country, it is significative to develop low-power YAG laser+TIG arc hybrid welding technique with high welding efficiency, low energy consumption and proprietary intellectual property rights, and it is benefit for the application and development of hybrid welding technique in industries. Therefore, low-power YAG laser (less than 500W) hybrid with TIG arc is used to weld and the characteristics of lower-power YAG laser+TIG arc welding process is studied. Low-power YAG laser+TIG hybrid welding technique with filler wire is developed. The variety of arc plasma behaviors and spectra in hybrid welding process is analyzed and the interaction between low-power YAG laser and TIG arc is discussed. Based on these, the phase matching mode between laser pulse and alternating current (AC) arc in low-power YAG laser+TIG arc hybrid welding process is controlled and the hybrid welding quality is improved. The main research contents are as follows:1. The characteristics of low-power YAG laser+TIG arc hybrid welding process (with or without filler wire) are investigated and the hybrid welding parameters of magnesium alloy and titanium alloy structures are obtained. The results indicate that the hybrid welding seam formation is good by single-side welding with both sides formation and the welding speed is much higher than TIG welding. The addition of filler wire avoids the defects of collapse and undercut. The hybrid welding penetration with back-feeding filler wire is two times deeper than that with front-feeding filler wire. The heat-affected-zone (HAZ) in hybrid welding joint with back-feeding filler wire is narrow and the grain size hardly grows, so the tensile strength of hybrid welding joint reaches 95% of base metal. Hybrid welding technique with filler wire supplies the feasibility to weld thick plates by low-power YAG laser+TIG arc hybrid welding process.2. The welding plasma behaviors and spectra are acquired and the effect of low-power YAG laser on welding plasma is studied. When laser beam act on the arc plasma and target metal, magnesium alloy is vaporized and ionized rapidly. The welding plasma intensifies and expands in a large extent. Especially in the negative wave of AC arc, the stability of arc plasma is improved significantly. The plasma spectra shows that there are only spectral lines of Mg I in laser welding and the intensities are weak. The spectra of TIG welding and hybrid welding processes consists of Mg I, Mg II, Ar I and Ar II lines. When laser beam is added, the intensities of spectral lines of Mg are much stronger than that in TIG welding, while the intensities of spectral lines of Ar are a little weaker than that in TIG welding. Spectral lines of Mg I are used to estimate the electron temperature and density of welding plasma and the results indicate that the electron temperature decreases and the electron density increases under the action of laser beam. The effects of laser beam on plasma behaviors, electron temperature and density in hybrid welding process with filler wire are weaker than that without filler wire. The threshold value of laser power which can intensify the TIG arc plasma is 50W-60W in hybrid welding process without filler wire and about 70W in hybrid welding process with filler wire.3. The weld seam formation, plasma behaviors, plasma spectra and arc voltage are analyzed and the interaction between low-power YAG laser and TIG arc plasma is studied. The results indicate that the interaction between low-power YAG laser and TIG arc includes the assistance effect of arc plasma on low-power YAG laser and the intensifying effect of YAG laser on arc plasma. On one hand, the action of TIG arc changes the surface condition of target metal and the initial condition of keyhole formation changes from the stage of heating base metal to the stage of plasma formation, which accelerates the process of keyhole formation in hybrid welding process. Meanwhile, the arc plasma and the Ar gas make the laser-induced plasma spray away from the workpiece with a gradient from the incident direction of laser beam, which weakens the absorption and defocusing effects of laser induced-plasma on laser beam. On the other hand, low-power YAG improves the stability of TIG arc plasma and expands the arc plasma with the concentration of the electric conducting channel with high temperature, which increases the arc voltage and arc energy density. The cooperation of both effects increases the welding penetration significantly.4. The effect of pulse laser wave and the phase matching between pulsed laser and AC arc on hybrid welding process is investigated. The phase matching controlling system of pulsed laser and AC arc is designed to control and improve the hybrid welding process. The results indicate that with the laser pulse energy as a constant, a high power density pulse with short duration is set at the beginning of pulse wave and the laser pulse duration is increased properly, which can accelerate the forming process of laser keyhole, intensify the impact effect of laser pulse on molten pool and increase the effecting time of laser keyhole on arc plasma, then the hybrid welding penetration increases with the percents of 15%～20%. The experimental results of phase matching mode between laser pulse and AC arc show that hybrid welding joints with high quality can be obtained whether the laser pulse acts on the positive wave or the negative wave. However, in hybrid welding process, it is helpful to improve the weld formation when laser pulse acts on the negative wave of AC arc. Meanwhile, both the power input and the spot force to base metal in the negative wave are higher than those in the positive wave, so the hybrid welding penetration with the phase matching mode that laser pulse acts on the negative wave of AC arc is 5%～10% higher than that of the positive wave.更多还原