双焦点光纤激光焊接特性及熔池行为研究

发布时间：2018-01-19 05:22

本文关键词： 双焦点激光焊接能场熔池流动行为焊丝熔化过渡非常规接头　出处：《哈尔滨工业大学》2017年博士论文　论文类型：学位论文

【摘要】：激光焊接技术与其他熔焊技术相比,在焊接精度、效率等方面具有明显的优势,已在汽车、航空航天等工业领域得到广泛应用。但在实际应用过程中发现,常规单焦点激光焊接仍然存在一定的局限性:一是激光光斑尺寸小、能量密度大,在激光深熔焊过程中易发生匙孔塌陷以及熔池剧烈波动的现象,影响焊缝质量;二是焊前对工件的装配精度要求高,焊接适应性较差。研究发现采用双焦点激光焊接方法可以有效解决上述问题,但目前关于双焦点激光焊接特性的研究不系统,相应的焊接机制至今仍不明确,不能有效指导双焦点激光焊接工艺的应用。针对上述问题,本文首先计算分析了双焦点光纤激光热源的能量密度分布(能场)特征,基于视觉传感方法系统研究了双焦点多种组合能场模式下的熔池表面动态特征及其对焊缝成形的影响,并结合有限元模拟方法对熔池内部匙孔与熔体流动行为进行了同步计算与分析,以此阐明双焦点焊接过程复杂能场对熔池行为的影响机制;进一步,分别针对激光填丝焊、非常规的十字交叉型接头开展双焦点激光熔丝特性、焊缝成形控制的研究,提出两种工况下最优的能场方案,并获得优质焊缝。首先,对不同能量比、间距条件下双焦点的能量密度分布特征进行测试与计算,并确定不锈钢材料激光深熔焊匙孔建立的临界功率密度;通过对不同双焦点能场作用下熔池表面物理特征及其焊缝成形的研究,建立了“能场特征—熔池行为—焊缝成形”三者之间的内在联系。试验结果发现,增大双焦点的光斑间距、双焦点能量密度相等及并行排布均会一定程度降低焊缝的熔化效率;当熔池中两匙孔串行排布时会在熔池宽度方向形成强流场,双焦点能场特征变化会改变熔池中匙孔数量、位置,导致该强流场作用方向和强弱的变化,从而影响最终的焊缝成形,即随光斑间距增大,焊缝熔深和熔宽均减小;随能量比增大,熔深先减小后增大,熔宽先增大后减小,在能量比为50/50时获得最小的熔深和最大的熔宽;并行排布熔深小于串行排布,熔宽则与焊接速度有关。为了进一步阐明双焦点不同匙孔状态下熔池内部的流动行为,建立了双焦点激光焊接三维瞬态热流耦合模型,并分析了熔池流动行为对焊缝成形和合金元素分布的影响。研究结果表明,当双焦点形成一个大尺寸匙孔时,纵截面上匙孔后部的回流漩涡消失,从而减小了对匙孔的冲击提高了匙孔稳定性;双匙孔串行排布时,金属蒸气反冲力的作用会导致匙孔中间熔体以较大流速向上流动,并增大了熔池表面宽度方向的流速,因此熔池宽度增大;增大光斑间距或双焦点能量密度不相等时会增大金属蒸气反冲力作用范围、改变金属蒸气反冲力作用方向,导致熔池宽度方向的流速降低,熔池宽度也相应减小;双匙孔并行排布时,整个熔池流动方向一致,因此熔池稳定性得到提高。双匙孔串行排布时熔体在横截面内形成具有较大流速的回流,更有利于合金元素在熔池内部扩散的均匀性。结合双焦点能量分布特征,开展了双焦点能场对熔丝行为改善作用的研究,获得优化的熔丝能场设计,发现采用并行排布双焦点激光焊接可以显著改善熔丝稳定性:常用的液桥过渡模式下,相比常规激光填丝焊,并行排布双焦点可进一步改善焊缝成形;常规激光填丝焊无法应用的熔滴过渡模式下,并行排布双焦点实现了焊丝的稳定熔化与过渡,显著提高了焊接稳定性。基于上述双焦点传热传质行为的基础研究,本文针对非常规的十字交叉型接头接合面难以熔合的难题,有效利用双焦点焊接能场设计的灵活性,采用双匙孔串行排布的焊接方案成功实现了双焦点激光焊接技术在非常规的十字交叉型接头上的应用,获得了成形良好、力学性能满足使用要求的焊接接头,验证了双焦点激光焊接技术在工业应用中的可行性与先进性。
[Abstract]:Laser welding technology compared with other welding technology in welding precision, has obvious advantages in efficiency, has been widely used in automotive, aerospace and other industrial fields. But in the practical application process, there are still some limitations of conventional single focus laser welding: one is the laser spot size, energy density large, prone to the keyhole in deep penetration laser welding in the process of collapse and the fluctuation of molten pool phenomenon, affecting the weld quality; two is the assembly precision of the workpiece before welding welding requirements, poor adaptability. The results show that using double focus laser welding method can effectively solve the above problem, but the current research on the characteristics of double focus laser welding the system, welding the corresponding mechanism is still not clear, can not effectively guide the application of double focus laser welding technology. Aiming at the above problems, this paper first analyzes calculation of double focus The energy density distribution of the fiber laser heat source (field) features, system visual sensing method is studied based on the combination of a variety of double focus can affect the dynamic characteristics of molten pool surface field mode and on the weld formation, combining finite element simulation method of keyhole and molten pool internal flow behavior were calculated and synchronization the analysis, in order to clarify the dual focus welding process can affect the mechanism of complex field on molten pool behavior; further, for laser welding with filler wire, non cross joint development of conventional double focus laser fuse characteristics, control of weld forming, put forward two conditions of the optimal energy field scheme, and obtain high quality welds. First of all, the different energy ratio, double focus energy density distribution measurement and calculation of space conditions, and determine the critical power of stainless steel laser welding keyhole is established based on the density; Study on forming the physical characteristics of the weld pool surface and weld under different double focus can, establish "the intrinsic link between field characteristics of molten pool behavior - Weld of the three. The test results show that the spot spacing increases double focus, double focus energy density equal and arranged in parallel will to some extent reduce the melting the efficiency of the weld pool; when the two key hole in the serial arrangement of strong flow field is formed in the width direction of the weld pool, double focus field will change the characteristics of keyhole molten pool in the number, position, lead to changes in the strong flow direction and intensity, thus affecting the forming of the final weld spot, with the increase of distance, the depth and width of weld were decreased; with the energy ratio increases, the penetration depth decreases first and then increases, the weld width increases first and then decreases, the energy ratio of 50/50 to obtain the minimum and maximum penetration weld width; the penetration depth is less than the serial parallel arrangement The arrangement, weld width and welding speed. In order to further clarify the flow behavior of internal double focus different keyhole state of molten pool, a welding 3D transient heat flow coupling model of double focus laser, and analyzed the influence of melt flow behavior of weld and alloy element distribution. The results show that when the double focus formation a large size hole, longitudinal section of the refluxing swirl keyhole rear disappeared, thereby reducing the impact of the keyhole improves the stability of the keyhole; double keyhole serial arrangement, effect of metal vapor recoil will lead to the key hole in the middle to large flow of melt flow upwards, and increased the pool the surface in the width direction of flow, so the pool width increases; spot spacing or double focus energy density is not equal will increase the metal vapor recoil range increases, change the direction of the metal vapor recoil effect, resulting in melting The pool in the width direction of the flow rate decreases, the pool width decreased; double hole parallel arrangement, the melt flow in the same direction, so the stability of molten pool is improved. Double keyhole serial arrangement of melt formation flow with large flow in cross section, more conducive to the alloy elements in the weld pool internal diffusion the uniformity of the combination of double focus energy distribution characteristics, carried out research on the field effect on improving the behavior of dual focus fuse, fuse can obtain optimal design field, using the parallel arranged double focus laser welding can significantly improve the stability of the fuse: liquid bridge transition mode is used, compared with conventional laser welding with filler wire can be further. To improve the weld arranged in parallel double focus; conventional laser welding with filler wire can not be applied to the droplet transfer mode, to achieve a stable melting and transition wire arranged in parallel double focus, improve the welding stability Based on the qualitative analysis. Based on the heat and mass transfer behavior of double focus, aiming at the problem of non cross joint conventional joints to fusion, effective use of double focus welding field design flexibility, the welding method of double keyhole serial arrangement successfully double focus laser welding technology in the application of non cross type joint the conventional, was in good shape. The mechanical properties of welded joints meet the use requirements, verify the feasibility of double focus laser welding technology in industrial applications and advanced.

【学位授予单位】：哈尔滨工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG456.7

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