铝合金激光液态填充焊的匙孔与熔池动态行为研究

发布时间：2018-04-06 20:06

本文选题：铝合金　切入点：激光液态填充焊　出处：《哈尔滨工业大学》2016年博士论文

【摘要】：目前,激光填丝焊技术广泛应用于航空、航天、汽车等领域。主要用于提高对接间隙的适应性,改善焊缝合金成分,调控焊缝区组织性能。一般来说,激光填丝焊的焊缝表面比激光自熔焊更光滑、均匀。由于激光光斑尺寸很小,激光填丝焊过程对光丝的对中精度与方向性要求较为严格。焊丝在送入过程中,会对入射激光有一定的反射,影响了激光能量的利用率,甚至造成焊接过程中激光能量的波动,焊接高反射率的铝合金时,这一影响尤为严重。激光填丝焊过程熔化的填材基本是沿匙孔壁前沿送入,直接影响了匙孔的稳定性。为此,本文针对铝合金材料的激光填丝焊技术,重点开展填材对匙孔与熔池动态行为的影响规律研究,开发新的填材送入方法以改善焊接过程的稳定性。论文系统研究了常规激光填丝焊过程填材对熔池、匙孔动态行为的影响规律,在此基础上提出了激光液态填充新方法,从熔池与匙孔表面的物理特性及焊接性能等方面,阐明并验证了液态填充方法对铝合金激光焊接过程稳定性的改善作用。同时,基于有限元模拟方法,阐明了填材不同送进位置对匙孔形态、熔池流动行为的影响机制。首先,基于先进的X射线透射系统实时监测熔池内部动态行为,研究了常规激光填丝焊过程填材对熔池流动行为、匙孔形态的影响规律,证明了熔化的填材沿匙孔边缘填充对匙孔有较大冲击作用,阻碍了内部金属蒸汽的快速逸出,在匙孔下部产生缩颈、闭合现象,匙孔底部诱发较多气泡;熔池内部的流动也更加复杂,在匙孔后方产生两个漩涡。高速焊接条件下,有利于降低匙孔底部的波动程度,减少了气泡的产生数量,熔池内部的流动轨迹变得简单,熔池后方的漩涡消失,由匙孔底部沿匙孔壁向熔池顶部流动的趋势增强,而且降低了焊缝气孔率。针对常规激光填丝焊存在的问题,提出了激光液态填充焊新方法:采用微小电弧预先熔化填材,让填材以液态形式沿熔池前方边缘缓慢流入熔池,激光能量仅仅用于建立熔池与匙孔。根据电弧熔化填材的状态,将填材分为了半熔态、全熔态两种填充模式。结果表明,激光液态填充焊增大了熔池尺寸、填材与匙孔的距离,避免了填材对匙孔的直接冲击,降低了铝合金焊缝气孔率。即使在15 m/min的高速焊接条件下,激光液态填充焊也能稳定熔化填材,获得很好的焊缝成形。可以适应的最大光丝对中偏移可达1.0 mm。为进一步揭示填材送入位置对熔池、匙孔内部的影响机制,建立了填材送入过程的三维瞬态激光焊接热-流耦合模型,阐明了填材送进位置对匙孔动态形貌、熔池流动行为的影响规律,提出匙孔前壁的最大凸起角作为匙孔稳定性的表征量。增大填材与匙孔之间的距离以及提高焊接速度,都可以减小匙孔前壁的最大凸起角,提高匙孔的稳定性。
[Abstract]:At present, laser wire filling welding technology is widely used in aviation, aerospace, automotive and other fields.It is mainly used to improve the adaptability of butt clearance, to improve the composition of weld alloy and to control the microstructure and properties of weld zone.Generally speaking, the weld surface of laser filler wire welding is smoother and more uniform than laser self-fusion welding.Because the size of laser spot is very small, the alignment accuracy and directivity of laser filler wire welding are strict.During the welding process, the wire will reflect the incident laser to a certain extent, which will affect the utilization rate of laser energy, and even cause the fluctuation of laser energy in the welding process, especially when welding aluminum alloy with high reflectivity.In the process of laser filling wire welding, the material melted is basically sent along the front of the keyhole wall, which directly affects the stability of the keyhole.In order to improve the stability of the welding process, this paper focuses on the study of the influence of the filler on the dynamic behavior of the keyhole and the molten pool, and develops a new feeding method to improve the stability of the welding process.In this paper, the influence of filler material on the dynamic behavior of molten pool and keyhole during conventional laser wire filling process is systematically studied. Based on this, a new method of laser liquid filling is proposed, which includes the physical characteristics and welding properties of the surface of molten pool and keyhole.The effect of liquid filling method on the stability of laser welding of aluminum alloy is clarified and verified.At the same time, based on the finite element simulation method, the mechanism of the influence of different feeding positions on the keyhole shape and the flow behavior of molten pool is explained.Firstly, based on the advanced X-ray transmission system to monitor the internal dynamic behavior of the molten pool in real time, the influence of the filling material on the flow behavior and keyhole morphology of the molten pool during conventional laser wire filling welding is studied.It is proved that the filling of the molten material along the edge of the keyhole has a great impact on the keyhole, which hinders the rapid escape of internal metal vapor, resulting in necking and closing in the lower part of the keyhole, and more bubbles are induced at the bottom of the keyhole.The flow inside the pool is also more complex, creating two swirls behind the keyhole.Under the condition of high speed welding, the fluctuation degree of the bottom of the keyhole is reduced, the number of bubbles is reduced, the flow path inside the molten pool becomes simple, and the vortex behind the molten pool disappears.The flow from the bottom of the keyhole to the top of the weld pool increases along the bottom of the keyhole and decreases the porosity of the weld.In view of the problems existing in conventional laser wire filling welding, a new method of laser liquid filling welding is put forward: the micro arc is used to melt the filler in advance, and the liquid material flows slowly into the molten pool along the front edge of the molten pool.Laser energy is used only to establish the molten pool and keyhole.According to the state of arc melting filler, the filling material can be divided into two filling modes: half melt state and full melting state.The results show that laser liquid filling welding increases the size of the weld pool, the distance between the filler and the keyhole, avoids the direct impact of the filler on the keyhole, and reduces the porosity of aluminum alloy weld.Even under the condition of 15 m/min high speed welding, laser liquid filling welding can stabilize the filling material and obtain good weld formation.The maximum centroid deviation of the adaptive optical fiber can reach 1.0 mm.In order to further reveal the influence mechanism of feed position on molten pool and keyhole, a three-dimensional transient laser welding thermal-flow coupling model was established, and the dynamic morphology of feed position of feed material to keyhole was clarified.The maximum protruding angle of the front wall of the keyhole is proposed as the token of the stability of the keyhole.The maximum protruding angle of the front wall of the keyhole can be reduced and the stability of the keyhole can be improved by increasing the distance between the filling material and the keyhole and increasing the welding speed.
【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】：2016
【分类号】：TG457.14

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