负压激光焊接过程蒸气羽烟及熔池行为研究

发布时间：2018-05-20 18:28

本文选题：局部负压 + 激光焊接　；参考：《上海交通大学》2015年博士论文

【摘要】：高功率激光焊接由于其高效及高品质的焊接质量,使其在中厚板构件的制造上体现出显著的优势。然而随着板厚的进一步增加,对激光功率及光束质量提出了更高的要求,且深熔焊接过程中的焊接缺陷也是制约高质量制造的关键问题之一。真空激光焊接的出现不但大大增加了焊接熔深,且有效提升了焊接质量,但真空室有限的空间尺寸限制了其在大型构件厚板激光焊接中的应用。为此,本文结合真空焊接的特点,提出了一种移动式负压激光焊接新方法,该方法为厚板大型构件的焊接制造提供了一条新途径。“低真空室”(又称“负压腔”)的构建是实现负压激光焊接的关键,该腔内的环境压力低于大气压力,将焊接部位置于该腔体内以实现焊接过程的局部负压环境。基于此装置,论文开展了负压环境下激光焊接过程中金属蒸气羽烟、熔池及小孔的动态行为的研究,进一步探讨了蒸气羽烟、熔池、小孔与激光能量之间的相互作用机制,从而揭示负压环境下的激光焊缝成形过程及缺陷抑制机理,为推动高功率激光在大型构件厚板焊接中的应用提供了理论和实验依据。首先,基于构建的全封闭负压腔光纤激光焊接实验平台,系统开展了不同负压环境下的激光焊接试验研究。其次,研究了不同负压环境下金属蒸气羽烟的动态变化特征,并基于光谱诊断分析了负压下激光焊接蒸气羽烟的频谱变化规律,进而分析了蒸气羽烟温度与环境压力的内在关联。研究了不同负压环境下蒸气羽烟对光纤激光能量的衰减特性及规律。进一步开展了不同环境压力下的焊接熔池及其小孔动态行为研究,分析了负压对焊接过程飞溅和气孔缺陷的抑制机理。最后,基于对全封闭负压腔激光焊接过程的研究结果,探讨了移动式局部负压环境下激光焊接过程中焊缝成形与蒸气羽烟及熔池动态行为的关系。全文的主要结论如下:1.环境压力对焊接熔深及截面形貌的影响存在着临界压力值,约为20 k Pa:当环境压力在101~20 k Pa内,熔深随环境压力降低而小幅增加,焊缝截面形貌主要特征为“Y”型;当环境压力降低至20 k Pa以下时,熔深开始大幅增加,且压力越低,熔深增加的幅度越大,在3 k Pa时的熔深约为常压时的2倍,焊缝截面形貌主要特征为“I”型。2.建立了负压环境下低合金高强钢厚板高功率激光焊接熔深与环境压力、激光功率、焊接速度的回归模型:0,方差分析拟合度为98.9%。该结果表明,焊接熔深随环境压力和焊接速度的减小而增大,随激光功率的增加而增加。当激光功率和焊接速度不变的情况下,焊接熔深与环境压力呈指数关系。3.发现了负压环境对金属蒸气羽烟的抑制规律,即最外侧扩散型羽烟、中部压缩羽烟及小孔附近驻留型羽烟被抑制的环境压力分别为101~80 k Pa、80~20 k Pa和20~3 k Pa。常压下光纤激光能量的衰减率约为11%,当环境压力降至3 k Pa时,金属蒸气羽烟对光纤激光能量的衰减率约为1%,驻留型金属蒸气羽烟为金属蒸气羽烟影响激光能量传递的主要部分。得出了金属蒸气羽烟对激光能量衰减率计算公式,4.发现了负压环境下蒸气羽烟动态变化特征与熔池及小孔行为的内在关联。随着环境压力的降低,金属蒸气羽烟摆动幅度较常压下减小,低于10 k Pa时趋于稳定,此时熔池表面波动降低,小孔稳定性增加,焊接质量明显提高。负压下小孔后壁的波动被抑制,焊接过程飞溅减少。同时负压加快了熔池内气泡逸出速度,缩短了其逸出路径,改变了其逸出位置,使焊缝气孔缺陷减少。5.基于气体流体动力学原理对局部负压腔的结构进行了优化,分析了负压腔尺寸和抽气孔位置对腔内压力分布和气流状态的影响。相比全封闭负压装置,采用局部负压装置获得了具有更高熔深的连续无缺陷激光焊缝。局部负压下的抽吸气流对驻留型金属蒸气羽烟有抑制作用,增加了激光的能量密度,同时抽吸气流对熔池的搅动作用有利于小孔对激光能量的吸收。
[Abstract]:Because of its high quality and high quality welding quality, high power laser welding shows remarkable advantages in the manufacturing of medium and thick plate components. However, with the further increase of the thickness of the plate, the laser power and the quality of the beam are higher, and the welding defects in the process of the deep welding are also the key problems to restrict the high quality manufacturing. One of them. The appearance of the vacuum laser welding not only greatly increases the welding depth, but also effectively improves the welding quality, but the limited space size of the vacuum chamber has limited its application in the laser welding of large plate thick plate. Therefore, a new method of moving negative pressure laser welding is proposed in this paper, which is thick with the characteristics of vacuum welding. This method is thick. A new way is provided for the welding of large plate members. The construction of "low vacuum chamber" (also called "negative pressure chamber") is the key to achieve negative pressure laser welding. The environment pressure in this cavity is lower than atmospheric pressure, and the welding position is placed in the cavity to realize the negative pressure environment of the welding process. In the process of laser welding, the dynamic behavior of metal vapour plume, molten pool and small hole is studied. The interaction mechanism between steam plume, molten pool, small hole and laser energy is further discussed, and the forming process of laser welds and the mechanism of defect suppression under the negative pressure are revealed, so as to promote the high power laser in the heavy plate of large components. The application in welding provides theoretical and experimental basis. First, based on the constructed fully enclosed negative pressure cavity optical fiber laser welding experimental platform, the system has carried out the laser welding experiment under different negative pressure environment. Secondly, the dynamic characteristics of the metal vapor plume under different negative pressure conditions are studied, and the negative pressure is analyzed based on the spectral diagnosis. The law of frequency spectrum change of vapor plume with laser welding is given, and the internal relationship between vapor plume temperature and environmental pressure is analyzed. The attenuation characteristics and laws of vapor feathers on optical fiber laser energy under different negative pressure conditions are studied. The dynamic behavior of weld pool and its small holes under different environmental pressure are further carried out, and the negative effect is analyzed. The mechanism of suppression of spatter and blowhole defects in welding process. Finally, based on the research results of the full closed negative pressure cavity laser welding process, the relationship between the weld formation and the dynamic behavior of the vapour plume and the molten pool during the laser welding process under the mobile local negative pressure environment is discussed. The main conclusions of the full text are as follows: 1. the welding depth of the ambient pressure on the welding The influence of the cross section morphology has a critical pressure value, which is about 20 K Pa: when the environmental pressure is in 101~20 K Pa, the weld depth is slightly increased with the decrease of ambient pressure, and the main feature of the weld section is "Y". When the environmental pressure is below 20 K Pa, the melting depth begins to increase substantially, and the lower the pressure, the greater the depth of the melting depth, at 3 K. The penetration depth of Pa is about 2 times that of normal pressure. The main feature of the weld cross section is "I" type.2., which establishes a regression model of high power laser welding depth and environmental pressure, laser power and welding speed in low alloy high strength steel thick plate under negative pressure environment: 0, the fitting degree of variance analysis is 98.9%. The result shows that welding depth is with environmental pressure and welding. With the increase of the speed, it increases with the increase of the laser power. When the laser power and the welding speed are constant, the welding depth is exponentially related to the ambient pressure..3. finds the inhibition law of the negative pressure environment to the metal vapor plume, that is, the most lateral diffused plume, the medium compressed plume and the resident plume near the hole. The ambient pressure is 101~80 K Pa, 80~20 K Pa and 20~3 K Pa. atmospheric pressure attenuation rate is about 11%. When the ambient pressure drops to 3 K Pa, the attenuation rate of metal vapor plume to fiber laser energy is about 1%. The main part of the laser energy transfer is the residing metal vapor plume as metal vapor plume. The calculation formula for the energy attenuation rate of the vapor plume is found. 4. the internal relationship between the dynamic characteristics of the vapour feathers and the behavior of the pores is found under the negative pressure. With the decrease of the ambient pressure, the amplitude of the metal vapor plume swings is less than that under the normal pressure, and it tends to be stable below 10 K Pa, and the fluctuation of the surface of the molten pool is reduced and the pore stability is stable. The welding quality is increased obviously. The fluctuation of the rear wall of the hole in the negative pressure is suppressed and the spatter in the welding process is reduced. At the same time, the negative pressure accelerates the escape velocity of the bubble in the molten pool, shortens the escape path and changes the escape position of the weld, and makes the weld hole defect reduction.5. based on the principle of gas flow dynamics to the structure of the local negative pressure cavity. The influence of the negative pressure cavity size and the suction hole position on the pressure distribution and the air flow state is analyzed. Compared with the full closed negative pressure device, the continuous defect free laser welds with higher melting depth are obtained by the partial negative pressure device. The suction flow under the local negative pressure has the inhibition effect on the residing type of the vapor plume, and the laser is added. The energy density and the stirring effect of the suction flow on the molten pool are beneficial to the absorption of laser energy by the small hole.
【学位授予单位】：上海交通大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG456.7

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