【作者】 胥国祥；

【导师】 武传松； Suck Joo Na；

【作者基本信息】 山东大学 ， 材料加工工程， 2009， 博士

【摘要】 激光+脉冲GMAW(pulsed gas metal arc welding,GMAW-P)复合热源焊作为一种新型的优质、高效焊接技术,综合了激光焊与GMAW-P工艺的双重优点,并具有“1+1＞2”的协同效应,工业应用潜力巨大。但目前对该项新技术的研究主要集中于工艺方面,即通过试验的方法优化工艺参数,而对其过程物理机制方面的研究极少。由于相对于单种焊接工艺,复合焊工艺参数较多,其物理过程也更加复杂,仅依靠试验优化工艺将需要花费较高的人力物力,不利于复合焊的推广应用。本文利用数值模拟技术,通过建立适用的热源模型对激光+GMAW-P复合热源焊的焊缝成形和热场特征进行研究,从而为复合焊物理机制研究及工艺参数的优化提供理论依据和参考数据,具有重要的学术理论意义和工程实用价值。根据激光深熔焊焊缝形状特征,分析了激光深熔焊热源作用的特点,将小孔效应体现在热流密度沿焊件厚度方向的分布上,建立了四种适用的、恰当的激光焊旋转体积热源模型,即热流峰值指数递增-锥体热源模型、热流峰值线性递增-对数曲线旋转体热源模型、热流峰值线性递增-抛物线旋转体热源模型和热流峰值双曲线递增-双曲线旋转体热源模型。在此基础上,从宏观的传热过程出发,对复合焊中来自电弧、过热熔滴和激光束的热输入分别进行描述,提出了四种复合焊组合式体积热源模型。组合式热源模型分别将电弧热输入、熔滴热焓和激光热能描述为双椭圆热源、热流平均分布的双椭球体热源和上述四种热流峰值递增-旋转体热源,并将三部分热能集成,构成适用的复合焊组合式体积热源模型。利用建立的组合式体积热源,对不同工艺条件下复合焊接准稳态温度场进行了数值分析,并计算出复合焊焊缝形状和尺寸。计算过程中,通过适当调节热源分布参数以间接反映激光-电弧相互作用对热流分布的影响。结果表明,焊缝形状尺寸的计算结果与实验结果总体吻合较好,但熔合线的局部走向仍有一定误差。针对此问题,对建立的四种复合焊组合式体积热源进行了如下改进:根据脉冲电弧的热作用特点,将复合焊中的脉冲电弧热能视为两个分别对应于峰值与基值电流电弧的分布参数不同的双椭圆热源,并通过适当减小焊件上表面电弧作用区域沿厚度方向的导热系数以间接反映电弧间歇性作用的特点。同时,对熔滴热源和激光热源的作用区域也进行了适当的调整。利用改进后的组合式体积热源模型,对复合焊的焊缝形状尺寸重新进行数值分析,计算精度大为提高,焊缝形状尺寸与熔合线走向都与实验结果吻合良好。应用已建立的复合热源焊的组合式体积热源模型,对激光+GMAW-P复合热源焊的热场进行数值分析,定量研究不同电弧功率对激光+GMAW-P复合热源焊热影响区宽度和热循环参数等热场特征基础数据的影响规律,并与纯激光焊、单GMAW-P的情况进行了比较,为从冶金上揭示复合热源焊的特点奠定了基础。为更合理地选定热源分布参数,将光线追踪法与线热源小孔模型相结合,较详细和准确地描述了激光束在非对称小孔内的多次反射过程以及孔壁对光能的Fresnel吸收,研发出新的小孔形状尺寸算法。将小孔尺寸与激光焊体积热源分布区域相联系,提出了基于小孔模型的激光焊体积热源模式。将此热源模式应用于激光焊和复合焊焊缝成形的数值模拟。结果表明,计算结果与实验结果吻合良好。更多还原

【Abstract】 As a new-style high-quality and high-efficiency joining technique,laser+pulsed GMAW(GMAW-P) hybrid welding combines the benefits of both laser beam welding (LBW) and GMAW-P and has the synergistic effect of "1+1>2".Thus,it is of significant potential in industrial applications.Up to now,however,most of studies on hybrid welding have just focused on the parameter optimization by experiments,and there is a lack of fundamental investigations involving its physical mechanism.Since hybrid welding involves more welding parameters compared with single welding process,its physical process is more complicated.So,determining the process parameters only by experiments requires vast amounts of manpower and material resources,thereby hindering its further spreading.In this study,using the numerical simulation technique,the weld formation and thermal field characteristics in laser+GMAW-P hybrid welding are investigated through developing the adaptive heat source model,thus providing the theoretical basis and reference data for study of heat transfer mechanism and welding parameter optimization,which is of great theoretical significance and practical value.After considering the geometry characteristics of weld cross section and analyzing the thermal action features in deep-penetration laser welding,four adaptive and suitable rotary volumetric heat sources for deep-penetration laser welding are developed,i.e.power peak density exponentially increasing-conic heat source,power peak density linearly increasing-logarithmic curve rotated body heat source,power peak density linearly increasing-parabolic curve rotated body heat source and power peak density hyperbolically increasing-hyperbolic curve rotated body heat source, which describe the keyhole effect though considering the heat flux distribution along the workpiece thickness direction.Based on this,from the point of view in macro heat transfer,the heat inputs from arc,overheated droplets and laser are described, respectively,and then four kinds of novel combined heat source models are built for laser+GMAW-P hybrid welding,which treat arc heat,droplet heat content and laser energy as a double-elliptic planar heat source,a double ellipsoid volumetric heat source with uniform power density and the four rotary volumetric heat sources mentioned above,respectively.The three parts of heat inputs are combined together to establish the combined volumetric heat source,which is suitable for hybrid welding.The quasi-steady temperature fields in hybrid welding for various welding conditions are analyzed numerically with the developed combined volumetric heat sources,and the weld shapes and dimensions are also calculated.In the calculations, the effect of the interaction between laser and arc on the heat flux distribution is considered indirectly though adjusting the distribution parameters of heat sources.The results show that the calculated weld geometries and dimensions agree well with the experimental data in the mass,but the predicted results of local fusion line loci have a discrepancy with the measured ones.Considering this problem,the following improvement of the developed four heat source models is made.Based on the thermal action characteristic of pulsed arc in laser+GMAW-P hybrid welding,the heat input of pulsed arc is regarded as two double elliptic planar heat sources with different distribution parameters corresponding to the peak and background arcs,respectively, and the intermittence of pulsed arc action is taken into account indirectly by using an appropriately lowered thermal conductivity along the workpiece thickness direction in the active domain of arc on the weldment top surface.Meanwhile,the action zones of heat sources for droplet heat content and laser heat are adjusted appropriately.Then, the weld shapes and sizes in hybrid welding are simulated again with the improved combined heat source models,both having a fair agreement with the experimental results,which indicates that the calculation accuracy of the combined volumetric heat source models are enhanced largely after their improvement.The developed combined heat source model is also employed to conduct the numerical analysis of thermal field in laser+GMAW-P hybrid welding.The influence of arc power on the characteristic parameters of thermal field,including width of heat affected zone(HAZ) and thermal cycle parameters,is quantitatively studied,and is compared with the calculated results of LBW and GMAW-P,which lays the foundation for revealing the characteristics of laser+GMAW-P hybrid welding in terms of metallurgy.In order to select the heat source distribution parameters more reasonably, through combining the ray tracing method with the keyhole model based on the line heat source to describe the multiple reflections of laser beam in the unsymmetrical keyhole and Fresnel absorption of laser energy by keyhole wall detailedly and correctly,a new method for calculating the keyhole shape and size is developed. Correlating the keyhole dimensions to the distribution domain of the volumetric heat source for laser welding,the volumetric heat source mode for laser welding based on the keyhole model is put forward.The weld formations in LBW and hybrid welding are simulated using the mode,and the calculated results are in good agreement with the experimentally determined data.更多还原