光纤激光焊接中厚板的底部驼峰形成机理的研究

发布时间：2018-05-13 01:42

本文选题：激光深熔焊接 + 底部驼峰缺陷　；参考：《湖南大学》2015年硕士论文

【摘要】：近年来,随着高功率、高光束质量光纤激光器的出现和发展,使激光深熔焊接技术在中厚板焊接制造领域中得到更进一步的研究。高功率光纤激光焊接中厚板过程中,激光功率密度可达106~108 W/cm2,导致其熔池在其动态过程中受力不平衡而极不稳定,容易形成飞溅、表面塌陷及底部驼峰等各种焊接缺陷,从而影响焊缝的各项性能。基于以上情况,为了能够实现高质高效的激光焊接中厚板,本文针对高功率光纤激光焊接厚度为5 mm的SUS 304不锈钢钢板的过程中出现底部驼峰的问题,研究小孔及熔池的动态变化过程,分析孔外金属蒸汽/等离子体的变化与底部驼峰的关系,对底部驼峰产生的机理进行试验研究。(1)阐述高功率激光焊接以及底部驼峰的研究现状,搭建基于高速相机拍摄的高功率光纤激光焊接实验平台。(2)基于改进的“三明治”新方法,采用高速相机从侧面直接观测到底部驼峰形成时整个焊接熔池下掉导致焊缝上表面塌陷,结果表明孔内金属蒸汽压力以及前沿孔壁液体凸起的向下动量克服小孔底部熔池表面张力的作用,导致熔融金属被推出内部熔池,继而向后流入驼峰。(3)使用高速相机从不同角度直接拍摄小孔开口、熔池及孔外金属蒸汽/等离子体动态流动过程,研究结果表明:表面张力作用是导致第一个底部驼峰产生及长大的重要原因;孔内熔融金属流动不连续,前沿孔壁凸起向下移动以及金属蒸发反冲压力,导致小孔底部熔池形成多个具有轮廓的熔滴,熔滴在表面张力以及熔池内部流动特征的作用下不断向后流动汇聚凝固形成底部驼峰。(4)在上下表面保护气体为Ar,维持流量及其吹气角度不变的情况下,采用改变单一变量的试验方法研究了激光功率,焊接速度,离焦量,下表面保护气体流量和焊接方位的变化对底部驼峰倾向的影响。结果表明合理的工艺措施,可有效地抑制底部驼峰的产生,改善焊缝质量。
[Abstract]:In recent years, with the emergence and development of high power and high beam quality fiber lasers, laser deep penetration welding technology has been further studied in the field of plate welding. In the process of high power fiber laser welding of medium and thick plate, the laser power density can reach 106108W / cm ~ 2, which results in unbalanced force and extremely unstable weld pool during its dynamic process, which is easy to form various welding defects such as spatter, surface collapse and bottom hump, etc. Thus, the properties of the weld are affected. Based on the above situation, in order to realize high quality and high efficiency laser welding plate, this paper aims at the problem of bottom hump in the process of high power fiber laser welding SUS 304 stainless steel plate with thickness of 5 mm. The dynamic process of the pore and molten pool is studied, and the relationship between the metal vapor / plasma outside the hole and the bottom hump is analyzed. The mechanism of bottom hump is studied experimentally. 1) the research status of high power laser welding and bottom hump is described, and the experimental platform of high power fiber laser welding based on high speed camera is built. A high-speed camera is used to observe directly from the side to the bottom of the hump, the whole weld pool falls down and the upper surface of the weld collapses. The results show that the pressure of metal vapor in the hole and the downward momentum of liquid protruding in the front hole wall overcomes the surface tension of the molten pool at the bottom of the hole, which results in the molten metal being pushed out into the inner molten pool. Then it flows backward into the hump. 3) using a high speed camera to directly photograph the orifice, the molten pool and the metal vapor / plasma flow outside the hole from different angles. The results show that the surface tension is the important cause of the first bottom hump, the flow of molten metal in the hole is discontinuous, the protruding and downward moving of the front hole wall and the recoil pressure of metal evaporation. Resulting in the formation of a plurality of profiled droplets in the molten pool at the bottom of the orifice, Under the action of surface tension and internal flow characteristics of the molten pool, the droplets continuously flow backward and solidify to form the bottom hump. 4) under the condition that the upper and lower surface protective gas is Arand the flow rate and the blowing angle are not changed, The effects of laser power, welding speed, defocusing amount, flow rate of lower surface shielding gas and welding azimuth on the bottom hump tendency were studied by changing a single variable. The results show that reasonable technological measures can effectively restrain the production of bottom hump and improve weld quality.
【学位授予单位】：湖南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG456.7

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