【作者】 杨志斌；

【导师】 陈彦宾；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2013， 博士

【摘要】 大型客机机身铝合金壁板结构由蒙皮与桁条组成，其轻量化加工制造是飞机制造领域的发展热点，空客公司以激光焊接技术代替原有铆接工艺，实现了减轻机身重量和降低成本的目标。现阶段，我国也在发展自己的大型客机，关于机身壁板结构的轻量化制造经过技术论证同样拟采用激光焊接技术。然而，该革新技术国际上仅有空客公司掌握并应用，国内尚属空白，亟需开展相关研究工作以突破并掌握机身壁板结构双侧激光焊接技术，为实现国产大型客机机身壁板结构的轻质、高效、低成本加工制造奠定坚实的理论基础，以缩短与空客公司在机身制造技术上的差距。针对这一特定需求，本文从最基础的工艺问题着手开展了铝合金机身壁板结构双侧激光焊接特征研究，充分理解焊缝成形质量、气孔缺陷及力学性能的控制工艺要点；研究了高速焊接条件下T型接头焊接过程的焊丝熔入特征；建立了双侧倾斜热源作用下的三维热-流耦合数学模型，借助数值模拟的手段从熔池流动行为角度深入理解双侧激光焊接的物理过程，获得了成形质量及气孔缺陷有效控制的理论依据。通过双侧激光焊接基础工艺试验研究发现，焊缝对称性、熔深及焊缝角度是体现T型接头成形质量的三个重要特征参数，其中光束姿态是关键影响工艺参数。光束间距决定了焊缝成形的对称性及微观组织的均匀性，减小入射角度可有效提高蒙皮与桁条的熔合能力并显著降低对蒙皮背部的热影响，光束入射位置偏移桁条有助于获得平滑过渡的焊缝角度。焊缝无损探伤结果表明，提高焊接速度与严格控制光束间距是抑制气孔缺陷的两个最重要的措施。T型接头双侧激光同步焊接的特点导致双侧热源相互交汇耦合，蒙皮侧热影响区明显宽于桁条侧是整个接头的最薄弱环节。结合机身壁板实际受力环境，对接头进行横向、轴向、纵向拉伸性能及横向拉压疲劳进行测试，测试结果表明接头轴向、横向拉伸性能与焊缝熔深密切相关，熔深控制在蒙皮厚度一半左右时抗拉强度达最大值，其横向、轴向、纵向抗拉强度分别达母材的87.8%、53.1%、90.8%，达到或者超过了空客公司的水准；接头的条件疲劳强度约为80.7MPa，为其静载强度的30%左右。针对长焊缝、多桁条、高速焊接容易出现焊接过程不稳定的问题，借助高速摄像手段分析了焊丝熔入特征的主要影响因素，结果表明：焊丝与激光束的相对位置关系是影响焊丝稳定熔入的关键，当光-丝部分重叠时，液态焊丝经焊丝端部与匙孔前沿间的“液桥”稳定、持续的流入熔池，焊接过程最稳定且成形美观，该过渡模式需具有两个必要条件：焊丝与工件接触，接触位置位于匙孔前沿。建立了三维准稳态T型接头双侧激光焊接过程热-流耦合数学模型，计算结果表明双侧热源交汇位置能量耦合效果显著，导致熔池最大长度位于热源交汇位置附近，匙孔上方出现明显对流，匙孔底部存在明显的漩涡流动，熔池尾部液态金属先流向熔池长度最大位置附近再流向熔池表面。匙孔贯通性消失导致匙孔底部漩涡流动更明显且更复杂，熔池尾部流向熔池底部的倾向更明显；匙孔同步性降低致使双侧熔池不对称，前后两匙孔间出现两个新的漩涡流动；提高焊接速度双侧热源能量耦合减弱，匙孔上方对流现象消失，熔池尾部完全流向熔池表面。匙孔贯通性、同步性及焊接速度的改变促使熔池流动行为发生变化是影响气泡从熔池内部逃逸几率的关键因素。保证匙孔贯通、控制匙孔同步及提高焊接速度均有助于提高气泡的逃逸几率。最后，采用双侧激光焊接技术成功实现了大尺寸铝合金机身壁板结构件(2000mm×1000mm)的焊接。焊缝成形及力学性能满足设计要求；焊接过程稳定，焊接速度最快可达12m/min。更多还原

【Abstract】 Lightweight processing and manufacturing of the large passenger aluminiumalloy aircraft panel structure is the hotspot in the aircraft manufacturing field，which is consist of skin and stringer. The Airbus had achieved the target of weightand costs reduction by using laser beam welding instead of the dominant rivetingtechnique. At present, our country is developing our own large aircraft, after fulltechnical appraisal and economic evaluation; the plan is to apply laser beamwelding technique to manufacture the aircraft panels. However, this innovativetechnology was only mastered by Airbus and still a blank in China. It isindispensable to carry out the related research work to breakthrough and masterthis technique. It will be a substantial theory basis for realizing the lightweightmanufacturing of China-made large passenger aircraft; also can shorten the gapwith Airbus in the fuselage panel manufacturing field.According to this specific requirement, in order to obtain the T-joints whichmeet the design requirements, we studied the double-sided laser beam weldingprocess, and researched the effects of the welding parameters on the weldappearance, porosity defects and mechanical properties in the present paper. Thefiller wire melting dynamics was also analysed. A3D mathematical model ofthermal-fluid coupling of double-sied laser beam welding was developed, with theaid of computational simulating to exactly understand what happens during thewelding process. Finally, we got the theoretical foundation for controllingeffectively the weld appearance and porosity defects.The experimental results showed that weld symmetrical characteristic, weldpenetration and weld seam were three main elements for evaluating the quality ofweld seam. The laser beam attitude was the key influence parameters. The beamdistance determined the symmetrical characteristic of the weld appearance and theuniformity of the microstructure. Reducing beam incident angles could increasethe fusion area between the skin and stringer; also reduce the thermal deformationof the skin panels. The beam incident position on the stringer was conducive toobtain smooth seam angle. Weld X-ray detection results show that increasewelding speed and control beam distance were two most important ways to reduceporosity defects.The characteristic of the double-sided laser beam welding of the T-jointsmade the two laser beam interaction with each other, resulting in the weld poolnear the skin retention high temperature for a long time and cooling speed was high. Therefore, the heat affected zone on the skin side was wider than that on thestringer side, resulting in it became the weakest area of the whole T-joint. Thetranserve, axial, longitudinal tensile tests and transerve pull-push fatigue test werecarried out according its actual stress conditions. The test results show that thetensile properties were decided by the weld penetratin, the tensile strength canreach a high level when the weld penetration was about half of the skin thickness.Its ranserve, axial, longitudinal tensile strengthes can reach87.8%、53.1%and90.8%of the base metal, which meets or surpasses the Airbus’s dates. Theconditioned fatigue strength was about80.7MPa, was30%of its tensile strength.Concerning the issue of welding process stablility under the special condition,we applied high speed photography to analyse the main influence of the filler wiremelting dynamics. The experimental results show that the laser-wire relatedposition was the main affecting factors of the filler wire melting dynamics. Whenlaser-wire partially overlapping, the liquid filler wire could through the liquidbridge between the wire tip and front keyhole smoothly and steadily flow into theweld melton pool, the welding process was stable and the weld appearance waswell. This transfer mode needs two necessary conditions: one is the filler wirecontact with the workpiece, the other one is the contact place located in front ofthe keyhole.A3D mathematical model of thermal-fluid coupling of double-sied laserbeam welding was developed. The numerical simulation results showed that thelaser energy coupling effect was remarkable; resulting in the longest size inside theweld pool located the coupling area and the convective flow was appeared abovethe keyhole. An obvious vortex was appeared under the keyhole. The liquid metalfirstly flowed to the bottom of the pool and then flowed to the surface.The disappearing of the keyhole contact condition resulted in the convectiveflow was completely disappeared and transferred to flow to the bottom of the weldmolten pool. The reducing of the keyhole synchronism resulted in the weld moltenpool was not symmetry, the trailing pool was flow into the leading pool, and twonew vortex flows were appeared between the two keyholes. Improve the weldingspeed resulted in the laser energy coupling effect was reduced, the convective flowwas completely disappeared and transferred to flow to the inside of the keyhole,and liquid metal was totally flow to pool surface. This was beneficial for pores toescape from the weld molten pool. Keep the keyhole linking, Symmetry andimprove welding speed are also good for pores to escape from the weld moltenpool.At last, we applied the double-sided laser beam welding to manufacture the large scale fuselage panel structure, the skin size was2000mm×1000mm. Theweld appearance and mechanical properties met the design requirements, and thewelding process was stable. The welding speed can reach up to12m/min.更多还原