本文選題：鋁合金　切入點：激光液態(tài)填充焊　出處：《哈爾濱工業(yè)大學(xué)》2016年博士論文

【摘要】：目前,激光填絲焊技術(shù)廣泛應(yīng)用于航空、航天、汽車等領(lǐng)域。主要用于提高對接間隙的適應(yīng)性,改善焊縫合金成分,調(diào)控焊縫區(qū)組織性能。一般來說,激光填絲焊的焊縫表面比激光自熔焊更光滑、均勻。由于激光光斑尺寸很小,激光填絲焊過程對光絲的對中精度與方向性要求較為嚴格。焊絲在送入過程中,會對入射激光有一定的反射,影響了激光能量的利用率,甚至造成焊接過程中激光能量的波動,焊接高反射率的鋁合金時,這一影響尤為嚴重。激光填絲焊過程熔化的填材基本是沿匙孔壁前沿送入,直接影響了匙孔的穩(wěn)定性。為此,本文針對鋁合金材料的激光填絲焊技術(shù),重點開展填材對匙孔與熔池動態(tài)行為的影響規(guī)律研究,開發(fā)新的填材送入方法以改善焊接過程的穩(wěn)定性。論文系統(tǒng)研究了常規(guī)激光填絲焊過程填材對熔池、匙孔動態(tài)行為的影響規(guī)律,在此基礎(chǔ)上提出了激光液態(tài)填充新方法,從熔池與匙孔表面的物理特性及焊接性能等方面,闡明并驗證了液態(tài)填充方法對鋁合金激光焊接過程穩(wěn)定性的改善作用。同時,基于有限元模擬方法,闡明了填材不同送進位置對匙孔形態(tài)、熔池流動行為的影響機制。首先,基于先進的X射線透射系統(tǒng)實時監(jiān)測熔池內(nèi)部動態(tài)行為,研究了常規(guī)激光填絲焊過程填材對熔池流動行為、匙孔形態(tài)的影響規(guī)律,證明了熔化的填材沿匙孔邊緣填充對匙孔有較大沖擊作用,阻礙了內(nèi)部金屬蒸汽的快速逸出,在匙孔下部產(chǎn)生縮頸、閉合現(xiàn)象,匙孔底部誘發(fā)較多氣泡;熔池內(nèi)部的流動也更加復(fù)雜,在匙孔后方產(chǎn)生兩個漩渦。高速焊接條件下,有利于降低匙孔底部的波動程度,減少了氣泡的產(chǎn)生數(shù)量,熔池內(nèi)部的流動軌跡變得簡單,熔池后方的漩渦消失,由匙孔底部沿匙孔壁向熔池頂部流動的趨勢增強,而且降低了焊縫氣孔率。針對常規(guī)激光填絲焊存在的問題,提出了激光液態(tài)填充焊新方法:采用微小電弧預(yù)先熔化填材,讓填材以液態(tài)形式沿熔池前方邊緣緩慢流入熔池,激光能量僅僅用于建立熔池與匙孔。根據(jù)電弧熔化填材的狀態(tài),將填材分為了半熔態(tài)、全熔態(tài)兩種填充模式。結(jié)果表明,激光液態(tài)填充焊增大了熔池尺寸、填材與匙孔的距離,避免了填材對匙孔的直接沖擊,降低了鋁合金焊縫氣孔率。即使在15 m/min的高速焊接條件下,激光液態(tài)填充焊也能穩(wěn)定熔化填材,獲得很好的焊縫成形�？梢赃m應(yīng)的最大光絲對中偏移可達1.0 mm。為進一步揭示填材送入位置對熔池、匙孔內(nèi)部的影響機制,建立了填材送入過程的三維瞬態(tài)激光焊接熱-流耦合模型,闡明了填材送進位置對匙孔動態(tài)形貌、熔池流動行為的影響規(guī)律,提出匙孔前壁的最大凸起角作為匙孔穩(wěn)定性的表征量。增大填材與匙孔之間的距離以及提高焊接速度,都可以減小匙孔前壁的最大凸起角,提高匙孔的穩(wěn)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.
【學(xué)位授予單位】：哈爾濱工業(yè)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG457.14

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本文編號：1718684