基于动网格的激光焊接小孔演变过程模拟
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摘要
在激光焊接过程中,激光向工件传输很高的能量密度,形成深宽比较大的焊缝,并且焊接时飞溅少、热影响区小、工件变形小、焊缝成形美观,这使得它在焊接领域的应用越来越广泛。当激光光斑上的功率密度足够大时(≥101 0 Wm2),金属在激光的照射下被迅速加热,工件表面的温度在极短的时间内上升到蒸发点,使金属材料熔化、汽化并蒸发,从而形成小孔,出现激光诱导的光致等离子体。小孔形成后,焊接过程中的能量吸收机制发生了质的改变,从小孔形成前的热传导为主的能量吸收,转变成为激光在小孔内部的多重反射吸收耦合等离子体的反韧致吸收机制。研究激光深熔焊接过程中的小孔演变具有重要的理论和实际意义,是现阶段激光焊接模拟仿真领域内主要的研究方向之一。
本研究采用软件FLUENT的动网格模型对激光焊接的小孔演变过程进行了模拟计算。首先,研究了激光焊接实际过程中的传热特点,对多种热源模型进行了介绍;研究了小孔孔壁的反射吸收在激光深熔焊接过程中对激光能量传输的作用和影响;采用几何光学近似的方法,通过光线跟踪技术,模拟了小孔内能量密度分布情况;对圆锥形小孔和抛物形小孔内平行激光束的能量密度分布进行了计算。
其次,根据激光焊接小孔演变的理论模型,计算了小孔界面在纯蒸发机制下的推移速度。将计算得到的速度经过适当的处理后作用于FLUENT中的动网格模型,使用FLUENT软件的网格重构功能,模拟了纯蒸发机制下温度场的分布和小孔的瞬时演变过程。
最后,结合光线追踪技术和动网格技术,在能量分布遵循高斯分布的平行激光作用下,模拟了ZL114和TC4的焊接小孔的演变过程,比较了激光深熔焊时这两种合金小孔演变过程的异同。
本研究基于FLUENT软件,首次采用移动网格界面跟踪技术实现了激光焊接小孔演变过程的模拟,在一定程度上,为激光焊接数值模拟系统的开发提供了小孔演变方面的理论依据和实现方法。
During the laser beam welding, a highly concentrated light energy is converted into thermal energy, so the weld seam has high depth-to-width ratio,and the process splash ,and the heat affect zone is small, as well as the weld form is nice. The laser beam welding is used more and more widely in the welding field. When the laser beam density reaches to the order of 101 0 W m2, strong evaporation occurs on the melt surface. The recoil pressure associated with energetic evaporation is sufficient to produce a deep, narrow depression in the molten material,which is called keyhole.
After the keyhole is formed, the energy-absorb-mechanism is changed qualitatively. Before the keyhole is formed, the laser beam energy is absorbed by the thermal conduction;after its formation,the energy absorption is changed into the laser beam’s multiple reflection and Fresnel absorption and inverse Bremsstranhlung absorption of the plasma in the keyhole. So, the study of the evolution of the keyhole in peneration laser welding has great theoretical and practical significance,and it is one of the most important research directions in the field of laser beam welding simulation at the present stage.
In this study, a computional simulation of the evolution of the laser welding keyhole is done, based on the software FLUENT’s dynamic mesh model.
First of all, the heat transfer characteristics are studied in the actual process of laser beam welding, and a wide range of heat source models are introduced. The effect of the multiple reflection and Fresnel absorption to the energy transfer is also studied.Then, according to geometrical optics theory, by laser tracing technology,the distribution of energy density in the keyhole is simulated. And the energy density distribution in cone-shaped and parabolic keyholes is calculated.
Secondly, according to the theoretical model of the evolution of keyhole, with the pure-evaporation-mechanism, the velocity of the keyhole surface is calculated. Then,with the dynamic mesh model and remeshing function in FLUENT software,the temperature distribution and transient evolution of keyhole are simulated .
In the end ,based on the technologies of laser tracing and dynamic mesh, laser welding keyhole’s evolution process of ZL114 and TC4 are simulated ,under the situations that the laser beam is parallel and the beam energy is flollow the Gaussian distribution function, as well as the similarities and differences between these two alloys’keyholes are compared and analysed.
Based on FLUENT, the study achieves the simulation of the evolution of keyhole by using the moving-mesh-interface-tracking technology, which provides a sound theoretical basis and implementation of keyhole evolution for the development of laser welding simulation system.
本研究采用软件FLUENT的动网格模型对激光焊接的小孔演变过程进行了模拟计算。首先,研究了激光焊接实际过程中的传热特点,对多种热源模型进行了介绍;研究了小孔孔壁的反射吸收在激光深熔焊接过程中对激光能量传输的作用和影响;采用几何光学近似的方法,通过光线跟踪技术,模拟了小孔内能量密度分布情况;对圆锥形小孔和抛物形小孔内平行激光束的能量密度分布进行了计算。
其次,根据激光焊接小孔演变的理论模型,计算了小孔界面在纯蒸发机制下的推移速度。将计算得到的速度经过适当的处理后作用于FLUENT中的动网格模型,使用FLUENT软件的网格重构功能,模拟了纯蒸发机制下温度场的分布和小孔的瞬时演变过程。
最后,结合光线追踪技术和动网格技术,在能量分布遵循高斯分布的平行激光作用下,模拟了ZL114和TC4的焊接小孔的演变过程,比较了激光深熔焊时这两种合金小孔演变过程的异同。
本研究基于FLUENT软件,首次采用移动网格界面跟踪技术实现了激光焊接小孔演变过程的模拟,在一定程度上,为激光焊接数值模拟系统的开发提供了小孔演变方面的理论依据和实现方法。
During the laser beam welding, a highly concentrated light energy is converted into thermal energy, so the weld seam has high depth-to-width ratio,and the process splash ,and the heat affect zone is small, as well as the weld form is nice. The laser beam welding is used more and more widely in the welding field. When the laser beam density reaches to the order of 101 0 W m2, strong evaporation occurs on the melt surface. The recoil pressure associated with energetic evaporation is sufficient to produce a deep, narrow depression in the molten material,which is called keyhole.
After the keyhole is formed, the energy-absorb-mechanism is changed qualitatively. Before the keyhole is formed, the laser beam energy is absorbed by the thermal conduction;after its formation,the energy absorption is changed into the laser beam’s multiple reflection and Fresnel absorption and inverse Bremsstranhlung absorption of the plasma in the keyhole. So, the study of the evolution of the keyhole in peneration laser welding has great theoretical and practical significance,and it is one of the most important research directions in the field of laser beam welding simulation at the present stage.
In this study, a computional simulation of the evolution of the laser welding keyhole is done, based on the software FLUENT’s dynamic mesh model.
First of all, the heat transfer characteristics are studied in the actual process of laser beam welding, and a wide range of heat source models are introduced. The effect of the multiple reflection and Fresnel absorption to the energy transfer is also studied.Then, according to geometrical optics theory, by laser tracing technology,the distribution of energy density in the keyhole is simulated. And the energy density distribution in cone-shaped and parabolic keyholes is calculated.
Secondly, according to the theoretical model of the evolution of keyhole, with the pure-evaporation-mechanism, the velocity of the keyhole surface is calculated. Then,with the dynamic mesh model and remeshing function in FLUENT software,the temperature distribution and transient evolution of keyhole are simulated .
In the end ,based on the technologies of laser tracing and dynamic mesh, laser welding keyhole’s evolution process of ZL114 and TC4 are simulated ,under the situations that the laser beam is parallel and the beam energy is flollow the Gaussian distribution function, as well as the similarities and differences between these two alloys’keyholes are compared and analysed.
Based on FLUENT, the study achieves the simulation of the evolution of keyhole by using the moving-mesh-interface-tracking technology, which provides a sound theoretical basis and implementation of keyhole evolution for the development of laser welding simulation system.
引文
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[35]肖兵,邓小珍.基于FLUENT的铝合金搅拌摩擦焊流动场模拟[J].南昌工程学院学报,2006,25(5):52~55
[36]张亚斌.基于FLUENT的铝合金电子束深熔焊三维流场数值模拟:[硕士学位论文].哈尔滨:哈尔滨工业大学,2007
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[2] D.R.osenthal,Davis.M,Kapadia.P. Some Aspecrt of the Fluid Dynamics of laser welding[J]. Journal of Fluid Mechanics,1983,126(7):123-146
[3] D.T.Swift-Hook,A.E.F.Gick. Penetration welding with laser[J]. Welding Journal, 1973,52(11):492～499
[4] J.G.Andrew,D.R.Atthey. Hydrodynamic limit to penetration of a material by a high power beam[J]. J.Phys.D:Appl.Phys,1976,9(12):2181～2194
[5] A.K.Kelmax. Heat model for laser welding[J]. Journal of Applied Physics,1978,51(2):941～947
[6] J.Mazumder,W.Steen. Heat transfer model for CW laser materials processing[J]. Journal of Laser Welding,1980,52(2):941～947
[7] J.M.Dowden,M.Davis,P.Kapadia. Molten region temperature distribution in laser welding[J]. J.Phys.D:Appl.Phys,1985,18(10):1987～1994
[8] N.Postacioglu,P.Kapadia,J.Dowden. Theoretical model of thermocapillary flows in laser welding[J]. J.Phys.D:Appl.Phys,1991,24(1):15～20
[9] Ichiko.O,Hamada.N,Soga.H. Development of the simulation Mode for 15KW CO2 Laser Materials Processing[J]. Laser Adcanced Materials Processing Science and Application(LAMP’87),Osaka,Japan,1987:31~36
[10] WEIPS,SHIAN M D. Three-dimensiona Analytical Temperature Field around the Welding Cavity production by a Moving Distributed High-intensity Beam[J]. ASME Journal of Heat Transfer,1993,15:848~856
[11] WEIPS,HOCY,SHIANMD,et all. Three-dimensiona Analytical Temperature Field and its Application to Solidification Characteristics in High-of Low-power-density beam Welding[J]. Int J.Heat mass Transfer,1997,40(10):2283~2292
[12] C.Lampa,A.kaplan,J.Powell,et all. An analytical thermadynamic model of laser welding[J]. J.Phys. D:Appl.Phys.,1997,Vol.30(3):1293~1299
[13] Sonti N,AmateauM F. Finite-elementmodeling ofheat flow in deep-penetration laser welds in aluminum alloys[J]. Numerical Heat Transfer,PartA,1989,16:351~378
[14]徐九华,罗玉梅,张靖周.高能束流小孔焊接模式传导过程的数值模拟[J].中国激光,2000,27(2):174~178
[15]张瑞华,片山聖二,内藤恭章等.基于旋转GUASS曲面体热源模型的激光焊接热过程的数值模拟[J].电焊机,2007,27(5):51~54
[16]蔡志鹏.焊接数值模拟中分段移动热源模型的建立及应用[J].中国机械工程学报,2002,13:208~210
[17] Bruno Martin,Alexandre Loredo,Michel Pilloz,et all. Characterisation of cw Nd:YAG laser keyhole dynamics[J]. Optics &Laser Technology,2001,33:201~207
[18] Wuzhu Chen,Xudong Zhang,Lei Jia. Peneration monitoring and control of CO2 laser welding with coaxial visual sensing system[J]. In:Proc. of SPIE:Lasers in Material Procesing and Manufacturing,2004,5629:129~140
[19]张旭东,陈武柱,刘春等. CO2激光焊接的同轴检测与熔透控制[J].焊接学报,2004,25(24):1~4
[20] Y.Arata,H.Maruo,I.Miyamoto,et all. Dynamic Behavior of Laser Welding and Cutting[C] , Proc.7th Int. Conf. On Electron and Ion Beam Science and Technology,1976,7:111~128
[21] Y.Arata,I.Miyamoto. Laser Welding. Technocrat,1978,11(5):33~42
[22] Y.Arata,N.Abe and T.Oda. Fundamental Phenomena in High Power CO2 Laser Welding(Report I)[J]. Transactions of JWRI,1985,14(1):5~11
[23] Y.Arata,N.Abe and T.Oda. Fundamental Phenomena in High Power CO2 Laser Welding(Report II)[J]. Transactions of JWRI,1985,14(2):17~22
[24] A.Matsunawa,J.D.Kim,et all. Dynamics of keyhole and molten pool in laser welding[J]. Journal of Laser Applications,1998,10(6):247~254
[25] Xiangzhong Jin,Lijun Li and Yi Zhang. A study on Fresnel absorption and reflections in the keyhole in deep penetration laser welding[J]. J.Phys.D:Appl. Phys.,35:2304~2310
[26]张屹.基于“三明治”新方法的激光深熔焊接小孔效应的模拟研究:[博士学位论文].长沙:湖南大学,2005
[27] P.Solana , J.Ocana. Mathematical model for penetration laser welding as a free-boundary problem[J]. J.Phys.D:Appl.Phy.,1997,30(9):1300~1313
[28] J.Kroos,U.Gratzke,C.Tix,et all. On the shape and location of the keyhole in penetration laser welding[J]. J.Phys.D:Appl.Phys,1993,26(3):481～486
[29]熊建钢.深熔激光焊接小孔和熔池形状数学模型及工艺参数ANN优化设计:[博士学位论文].武汉:华中科技大学图书馆,2001
[30]熊建钢,胡强,李志远等.深熔激光焊接数学模型研究现状[J].中国机械工程,2003,14(9):803-807
[31]王智勇,初新俊,陈虹等.激光深熔焊接抛物面小孔模型[J].焊接学报,2006,27(2):1~5
[32]金湘中.激光深熔焊接小孔效应的理论和试验研究:[博士学位论文].长沙:湖南大学,2002
[33]朱立奎,雷永平,史耀武. FLUENT在焊接模拟中的应用[J].电焊机,2007,37(8):13~19
[34]王宏,史耀武,巩水利等.激光深熔焊过程中保护区特征尺寸的数值模拟[J].中国激光,2006,3(3):417~422
[35]肖兵,邓小珍.基于FLUENT的铝合金搅拌摩擦焊流动场模拟[J].南昌工程学院学报,2006,25(5):52~55
[36]张亚斌.基于FLUENT的铝合金电子束深熔焊三维流场数值模拟:[硕士学位论文].哈尔滨:哈尔滨工业大学,2007
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