激光穿孔点焊接瞬态过程数值分析
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摘要
考虑工件表面等离子体作用,建立了小孔和熔池传热与传质耦合的穿孔点焊数值分析模型.采用随小孔形状变化的自适应热源模型,热源形态依小孔形状变化而实时改变.模型考虑了蒸发现象所引起的质量转换和能量损失,利用焓–孔介质法处理焊接过程动量损耗.主要考虑液态金属蒸发所带来的反冲压力、表面张力和液体静压力并通过流体体积方程计算小孔壁面.结果表明,小孔形成直至穿孔过程都可能产生向上和向下的飞溅、焊瘤和余高.激光的瑞利散射、工件表面等离子体的热效应,激光束反射和等离子体膨胀作用,使得工件上/下的焊缝宽度比中间略大.模拟计算值与试验结果比较,二者在形状和尺寸基本吻合.
Considering plasma effect on the surface of the workpiece, a numerical simulation model of keyhole and weld pool coupled with heat and mass transfer was established.The adaptive heat source model was used with the change of shape of keyhole in real time. Mass transfering and energy lossing caused by evaporation was considered in the model,and the momentum sinking due to solidification was dealt with enthalpy-porosity technique. The keyhole wall was calculatedby fluid volume equation, mainly considering recoil pressure induced by the metal evaporation, surface tension and hydrostatic pressure. The results demonstrated that, spatters are shaped such as weld flash and reinforcement after keyhole formation and perforation. The upper and lower welding width is slightly larger than the middle induced by raleigh scattering of laser, reflection and expansion of plasma. The calculated values were basically consistent with the experimental results in shape and size of the weld.
Considering plasma effect on the surface of the workpiece, a numerical simulation model of keyhole and weld pool coupled with heat and mass transfer was established.The adaptive heat source model was used with the change of shape of keyhole in real time. Mass transfering and energy lossing caused by evaporation was considered in the model,and the momentum sinking due to solidification was dealt with enthalpy-porosity technique. The keyhole wall was calculatedby fluid volume equation, mainly considering recoil pressure induced by the metal evaporation, surface tension and hydrostatic pressure. The results demonstrated that, spatters are shaped such as weld flash and reinforcement after keyhole formation and perforation. The upper and lower welding width is slightly larger than the middle induced by raleigh scattering of laser, reflection and expansion of plasma. The calculated values were basically consistent with the experimental results in shape and size of the weld.
引文
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[2]Zhou J,Tsai H L.Investigation of mixing and diffusion processes in hybrid spot laser-MIG keyhole welding[J].Journal of Physics D:Applied Physics,2009,42:1-15.
[3]庞盛永,陈立亮,殷亚军,等.激光焊接瞬态小孔与运动熔池行为模拟[J].焊接学报,2010,31(2):71-73.Pang Shengyong,Chen Liliang,Yin Yajun,et al.Simulations of transient keyhole and dynamic melt pool behaviors during laser welding[J].Transactions of the China Welding Institution,2010,31(2):71-73.
[4]汪任凭,雷永平,史耀武,等.激光深熔焊中匙孔形成过程的动态模拟[J].焊接学报,2010,31(11):38-40.Wang Renping,Lei Yonglei,Shi Yaowu,et al.Numerical simula-tion of keyhole formation process in laser deep penetration welding[J].Transactions of the China Welding Institution,2010,31(11):38-40.
[5]Matsunawa A,Mizutani M,Katayama S,et al.Porosity formation mechanism and its prevention in laser welding[J].Welding International,2003,17(6):431-437.
[6]Mickael C,Muriel C,Philippe L M,et al.A new approach to compute multi-reflections of laser beam in a keyhole for heat transfer and fluid flow modelling in laser welding[J].Journal of Physics D:Applied Physics,2013,46:1-14.
[7]Zhao H Y,Niu W D,Zhang B,et al.Modelling of keyhole dynamics and porosity formation considering the adaptive keyhole shape and three-phase coupling during deep-penetration laser welding[J].Journal of Physics D:Applied Physics,2011,44:1-13.
[8]Rai R,Burgardt P,Milewski J O,et al.Heat transfer and fluid flow during electron beam welding of 21Cr-6Ni-9Mn steel and Ti6Al4V alloy[J].Journal of Physics D:Applied Physics,2009,42:1-12.
[9]张屹,刘西霞,史如坤,等.基于Level-Set方法的小孔及熔池动态形成数值模拟[J].焊接学报,2016,37(4):29-34.Zhang Yi,Liu Xixia,Shi Rukun,et al.Numerical simulation of deep-penetration laser welding based on level-set method[J].Transactions of the China Welding Institution,2016,37(4):29-34.
[10]李岩,冯妍卉,张欣欣,等.考虑小孔演变的等离子弧焊接动态热源模型及验证[J].金属学报,2013,49(7):804-810.Li Yan,Feng Yanhui,Zhang Xinxin,et al.A dynamic heat source model with respect to keyhole evolution in plasma arc welding[J].Acta Metallurgica Sinica,2013,49(7):804-810.
[11]李天庆.等离子弧热-力作用随熔池穿孔动态演变过程的数值分析[D].济南:山东大学,2014.
[12]张涛,武传松,陈茂爱,等.穿孔等离子弧焊接熔池流动和传热过程的数值模拟[J].金属学报,2012,48(9):1025-1032.Zhang Tao,Wu Chuansong,Chen Maoai,et al.Modelling fluid flow and heat transfer phenomena in keyholing stage of plasma arc welding[J].Acta Metallurgica Sinica,2012,48(9):1025-1032.
[13]Siegman A E.Defining,measuring,and optimizing laser beam quality[J].SPIE,1990,1224:2-13.
[14]胥国祥,张卫卫,刘朋,等.激光+GMAW复合热源焊熔池流体流动的数值分析[J].金属学报,2015,51(6):713-723.Xu Guoxiang,Zhang Weiwei,Liu Peng,et al.Numerical analysis of fluid flow in Laser+GMAW hybrid welding[J].Acta Metallurgica Sinica,2015,51(6):713-723.