Research On The Interaction Mechanism And Process Of YAG Laser+pulse Twin-MIG Hybrid Welding

YAG laser+pulse twin-MIG arc hybrid welding is a new joining technologybased on laser welding and tandem welding, which is the development of laser+archybrid welding. Currently, hybrid welding researches mainly focus on the applicationsof welding procedure and simulation of laser+single arc hybrid welding, but less onlaser+twin-arc hybrid welding.In addition to interactions of laser and arcs, there is also complex co-actionbetween the two arcs in YAG laser+pulse twin-MIG arc hybrid welding process. Asdirect heat sources, laser and arc have significance to welding process. Wire-wiredistance, angle between the wires, power supply mode and laser spot location all caninfluence thermal field, force field, magnetic field and coupling mechanism betweenthe heat sources, and then affect droplet transfer, weld appearance and microstructure.So sophisticated understanding of interactions between laser and arc can offerguidance for further practical research of YAG laser+pulse twin-MIG arc hybridwelding technology. In the paper, characteristic of welding technology and theinteraction mechanism between laser and arcs are investigated in the YAG laser+pulse twin-MIG arc hybrid welding of Q235mild steel.1. The welding technology of YAG laser+pulse twin-MIG arc hybrid welding isinvestigated using self-built welding system. The results indicate that: in YAG laser+pulse twin-MIG arc hybrid welding, flow mode of molten pool is altered after theinput of YAG laser, compared with twin-MIG welding, the flow mode of hybridmolten pool is helpful to force high-temperature liquid metal flow downward, andweld penetration increase accordingly. Because of much metal vapor and high densityelectron, laser spot location can offer a stable cathode spot for arcs. It is helpful toprevent the formation of undercut on the weld surface and make the weld formingcontinuous. The microstructure in weld center and heat affected zone produced byYAG laser+pulse twin-MIG arc hybrid welding is basically the same as that oftwin-arc welding. Proeutectoid ferrite along the grain boundary is less and smaller inhybrid welding.2. The arc behavior, droplet transfer, electrical signal and arc spectrum signal ofYAG laser+pulse twin-MIG arc hybrid welding process are recorded by high-speedcamera, DAQ card and spectrograph synchronously. The results indicate that thehybrid arcs are attracted to the laser-heated spot and the cross-section of hybrid arc column is constricted obviously. Voltage needed for arc ignition and combustiondecrease and stability of hybrid welding is prominent, especially in high-speedwelding. When laser-arc distance and arc-arc distance is optimal, electron in laserplasma is in equilibrium under the action of Lorentz force and electromagnetic force.Electrons evenly distributed at both side of the laser plasma to offer stable cathodespot. Internal equilibrium of laser plasma is broken because of short distance or laserdeviation, which lead to unstable of cathode spot. Laser plasma and arc plasmaseparate with each other and serve no purpose whatsoever in large distance. Droplettransfer frequency of hybrid welding reduces under the coactions of laser heat effect,reactive force offered by high temperature plasma and surface tension, which makesthe gravity of hybrid droplet is about2times than that of twin-arc droplet. Comparedwith twin-arc hybrid welding, droplet transfer frequency of hybrid welding decreasesby10~20%。3. Study on spatial distribution of radiation intensity, electron temperature anddensity of hybrid plasma indicate spectrum radiation, electron temperature and densitydistribution of hybrid plasma increase at the concentrated zone of hybrid arc columnbut there is no evident difference in the area far from concentrated zone. Electrontemperature near laser plasma increases with laser power but decreases with wire-wiredistance. Hybrid plasma of YAG laser+pulse twin-MIG arc hybrid welding is in alocal thermal equilibrium condition.4. Largest Lyapunov exponent (LLE) of current data in YAG laser+pulsetwin-MIG arc hybrid welding is calculated in term of non-linear theory. The resultsindicate YAG laser+pulse twin-MIG arc hybrid welding is a complex chaotic process.LLE is closely related to stability of welding process: the more stable the weldingprocess, the smaller LLE and its standard deviation. The smallest LLE can beacquired when welding technology is optimum. LLE can serve as evaluation index ofstability of.YAG laser+pulse twin-MIG arc hybrid welding process.