Numerical Analysis Of Double-Wire GMAW And Laser+Double-Wire GMAW Hybrid Welding

GMAW (Gas Metal Arc Welding) is one widely applied arc welding method withhigh productivity, good welding quality, low production cost, easy to realizeautomation and intellectualization. Based on computational fluid dynamics softwareFLUENT, the welding process of double-wire GMAW (DW-GMAW) andlaser+double-wire GMAW hybrid (LDW-GMAW) including metal transfer and arcbehavior is numerical analysed in this thesis. Meanwhile, the electrical signal,high-speed photography and spectral measurement are utilized and the simulatedresults are verified, the reliability and accuracy of the simulated results are proved.The achievement improves the understanding for the effect of welding parameters onmetal transfer and arc behavior and provides theoretical guidance and reference forformulating welding technology.Firstly, the welding process of single-wire GMAW (SW-GMAW) is numericalanalyzed. The critical transion current is obtained when the globular transfer modechanges to the spray transfer mode. For the simulation of metal transfer, it is dividedto with thermal analysis and without one. The comparison shows that the simulatedresults are good when the thermal analysis is considered. The results show that withthe surface tension coefficient increasing, the volume of detached droplet increasesobviously and the length of liquid between the inlet of wire and detached dropletdecreases. As dynamic viscosity increases, the length of liquid increases but thevolume changes little. Combined the electric potential distribution and electricalsignal and high-speed photography in the welding experiment, it shows that when thedroplet detaches the welding wire, the current don’t flow the detached droplet.Secondly, the welding process of DW-GMAW is numerical analyzed. For metaltransfer, due to the electromagnetic force between two arcs in DW-GMAW, it is foundthat a droplet transfers axially in SW-GMAW, but non-axially in DW-GMAW. Forwelding arc, For SW-GMAW, the current density at the workpiece can be describedby Gaussian assumption. For DW-GMAW, the distribution of current density isrelated to the interwire distance. When the interwire distance is small enough, thecurrent density at the workpiece can be described by Gaussian assumption. InDW-GMAW, the influence of welding current, interwire distance, shielding gas flow,equal and unequal current on the arc behavior are studied. It is found that with thewelding current increasing, the arc inclined degree, the maximum arc temperature and the peak of heat flux on the base metal surface increase, and the distribution of heatflux changes from double-peak to one-peak. While the interwire distance is largeenough, the Gaussian assumption for the current density should be modified. With theinterwire distance increasing, the arc shape changes from single-arc to double-arc andthe distribution of current density on the base metal surface changes from one-peak todouble-peak. The peak of current density increases firstly and then decreases. Whenthe interwire distance reaches to the extent, the peak of current density remainsunchanged basically. Moreover, the peak of heat flux and pressure decreases firstlyand then increases. When the gas flow increases, the peak of pressure increases andthat the maximum arc temperature increases firstly and then decreases. There isoptimum gas flow for the welding. Compared equal current with unequal current, thepeak value is basically the same for equal current and the peak value is different andthe larger peak appears on the side of the welding arc carrying higher current forunequal current.Finally, the arc behavior in LDW-GMAW is numerical analyzed based on thethree-dimension mathematical model. It is found that compared to DW-GMAW, thearcs are attracted and compressed by the laser. Adding laser, the pressure decreasesand the arcs energy become more concentrated. The peak of heat flux with laser istwice of that without laser. It benefits to the welding at high speed and obtain highpenetration avoiding undercut and dump. The influence of laser power, laserdefocusing distance and laser-arc separation on arc behavior in LDW-GMAW isstudied. The results show that as laser power increases, the arc inclined degree and thepeak of heat flux increases. With the laser-arc separation increasing from positivevalue to negative one, the heat flux increases firstly and then decreases. The peak ofheat flux appears when the defocusing distance is0mm. Due to the limited radius oflaser plasma, when the distance between laser and arc is large enough, it leads to theinteraction between laser and arcs weakened and even disappeared. Therefore, inorder to maximize the effect of the laser on arcs, the laser-arc separation should bereasonably chosen.