| Laser +GMAW hybrid welding combines the advantages of both laser welding and GMAW welding that with great potential to realize high quality and high efficiency welding of aluminum alloy.However,the welding parameters for Laser +GMAW hybrid welding are complex that it is very difficult to optimize them.During the welding process,the fluid flow in the weld pool is closely related to the weld bead formation.Therefore,it has great theoretical value and practical value to study the dynamic behavior of the welding pool of aluminum alloy by numerical simulation.In this paper,based on the principles of heat transfer,optics and fluid dynamics and together the coupling of gas,liquid and solid phase as well as the interaction mechanism between the droplet,the keyhole and the molten pool,a 3D transient molten pool of aluminum alloy numerical analysis model of fluid flow by laser +GMAW hybrid welding is established based on software FLUENT.In this model,arc heat input is simulated as by using the double-ellipsoid heat source while laser heat input is described as the conical heat source which has adjustable peak power density and its distribution parameters could be determined by simplified keyhole model's geometrical size.Firstly,the droplet transfer process is considered as the process of flowing into the molten pool from the upper specific area of the molten pool and the periodic function of liquid metal flow velocity versus time function is used to characterize the droplet transition frequency.Secondly,the inflow of liquid metal is set as boundary velocity-inlet and the keyhole is regarded as the deformation of the molten pool caused by the laser induced reaction force in FLUENT.In order to simplify the calculation process,the main influence of keyhole on the flow pattern of molten pool was mainly taken into account.Numerical calculation of pore shape,fluid flow and temperature field in molten pool is carried out by the established three dimensional numerical model through different laser power toward laser cladding and fillet welding process and the analysis of flow characteristics of laser +GMAW hybrid welding with different joints was also been done.The results show a good agreement between the main characteristics of curved keyhole and the fluid flow pattern of hybrid welding.In the process of laser cladding,the dynamic characteristics of the hybrid welding pool are greatly affected by the arc and droplet and without eddy under the action of 2kW laser power.With the increase of laser power,laser induced reaction force was enhanced and the flow field becomes more complex.When the laser power increases to 5kW,keyhole depth becomes relatively stable while the basic flow pattern of liquid metal showed 5kW no difference with laser power 3kW.With the increase of laser power,the rate of fluid flow increases and the heat transfer mode of the hybrid welding molten pool changes into convective heat transfer gradually.In the process of fillet welding,when laser power is set to 0kW,due to molten pool in the characteristics of gravity distribution,a serious downward flow of molten pool in vertical plate is showed and the sunken is also showed in vertical plate molten pool with serious asymmetry of molten pool.When laser power is set to 2kW,laser keyhole is not produced and the flow pattern of molten pool is changed due to the addition of laser while weld pool asymmetry is improved,and the flow pattern of molten pool is basically the same as 0kW.When laser power is set to 2kW,laser keyhole is produced and the sunken is firstly showed in keyhole,fluid flow patterns tend to be complex and the asymmetry of welding pool is improved significantly at the same time.In addition,the metal accumulation in the keyhole wall is the main reason for the formation of bubbles in the welding process of the fillet hybrid welding and bubbles appear mainly at the bottom of the keyhole and then float up with buoyancy. |
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