Numerical Simulation Of Weld Formation In Laser+GMAW-P Hybrid Welding

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.