本文關鍵詞： 雙焦點激光焊接 能場 熔池流動行為 焊絲熔化過渡 非常規(guī)接頭　出處：《哈爾濱工業(yè)大學》2017年博士論文　論文類型：學位論文

【摘要】：激光焊接技術與其他熔焊技術相比,在焊接精度、效率等方面具有明顯的優(yōu)勢,已在汽車、航空航天等工業(yè)領域得到廣泛應用。但在實際應用過程中發(fā)現(xiàn),常規(guī)單焦點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,在激光深熔焊過程中易發(fā)生匙孔塌陷以及熔池劇烈波動的現(xiàn)象,影響焊縫質量;二是焊前對工件的裝配精度要求高,焊接適應性較差。研究發(fā)現(xiàn)采用雙焦點激光焊接方法可以有效解決上述問題,但目前關于雙焦點激光焊接特性的研究不系統(tǒng),相應的焊接機制至今仍不明確,不能有效指導雙焦點激光焊接工藝的應用。針對上述問題,本文首先計算分析了雙焦點光纖激光熱源的能量密度分布(能場)特征,基于視覺傳感方法系統(tǒng)研究了雙焦點多種組合能場模式下的熔池表面動態(tài)特征及其對焊縫成形的影響,并結合有限元模擬方法對熔池內部匙孔與熔體流動行為進行了同步計算與分析,以此闡明雙焦點焊接過程復雜能場對熔池行為的影響機制;進一步,分別針對激光填絲焊、非常規(guī)的十字交叉型接頭開展雙焦點激光熔絲特性、焊縫成形控制的研究,提出兩種工況下最優(yōu)的能場方案,并獲得優(yōu)質焊縫。首先,對不同能量比、間距條件下雙焦點的能量密度分布特征進行測試與計算,并確定不銹鋼材料激光深熔焊匙孔建立的臨界功率密度;通過對不同雙焦點能場作用下熔池表面物理特征及其焊縫成形的研究,建立了“能場特征—熔池行為—焊縫成形”三者之間的內在聯(lián)系。試驗結果發(fā)現(xiàn),增大雙焦點的光斑間距、雙焦點能量密度相等及并行排布均會一定程度降低焊縫的熔化效率;當熔池中兩匙孔串行排布時會在熔池寬度方向形成強流場,雙焦點能場特征變化會改變熔池中匙孔數(shù)量、位置,導致該強流場作用方向和強弱的變化,從而影響最終的焊縫成形,即隨光斑間距增大,焊縫熔深和熔寬均減小;隨能量比增大,熔深先減小后增大,熔寬先增大后減小,在能量比為50/50時獲得最小的熔深和最大的熔寬;并行排布熔深小于串行排布,熔寬則與焊接速度有關。為了進一步闡明雙焦點不同匙孔狀態(tài)下熔池內部的流動行為,建立了雙焦點激光焊接三維瞬態(tài)熱流耦合模型,并分析了熔池流動行為對焊縫成形和合金元素分布的影響。研究結果表明,當雙焦點形成一個大尺寸匙孔時,縱截面上匙孔后部的回流漩渦消失,從而減小了對匙孔的沖擊提高了匙孔穩(wěn)定性;雙匙孔串行排布時,金屬蒸氣反沖力的作用會導致匙孔中間熔體以較大流速向上流動,并增大了熔池表面寬度方向的流速,因此熔池寬度增大;增大光斑間距或雙焦點能量密度不相等時會增大金屬蒸氣反沖力作用范圍、改變金屬蒸氣反沖力作用方向,導致熔池寬度方向的流速降低,熔池寬度也相應減小;雙匙孔并行排布時,整個熔池流動方向一致,因此熔池穩(wěn)定性得到提高。雙匙孔串行排布時熔體在橫截面內形成具有較大流速的回流,更有利于合金元素在熔池內部擴散的均勻性。結合雙焦點能量分布特征,開展了雙焦點能場對熔絲行為改善作用的研究,獲得優(yōu)化的熔絲能場設計,發(fā)現(xiàn)采用并行排布雙焦點激光焊接可以顯著改善熔絲穩(wěn)定性:常用的液橋過渡模式下,相比常規(guī)激光填絲焊,并行排布雙焦點可進一步改善焊縫成形;常規(guī)激光填絲焊無法應用的熔滴過渡模式下,并行排布雙焦點實現(xiàn)了焊絲的穩(wěn)定熔化與過渡,顯著提高了焊接穩(wěn)定性�；谏鲜鲭p焦點傳熱傳質行為的基礎研究,本文針對非常規(guī)的十字交叉型接頭接合面難以熔合的難題,有效利用雙焦點焊接能場設計的靈活性,采用雙匙孔串行排布的焊接方案成功實現(xiàn)了雙焦點激光焊接技術在非常規(guī)的十字交叉型接頭上的應用,獲得了成形良好、力學性能滿足使用要求的焊接接頭,驗證了雙焦點激光焊接技術在工業(yè)應用中的可行性與先進性。
[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.

【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG456.7

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