| The YAG laser+MAG arc hybrid welding technology, not only make full use of the advantages of normal YAG laser welding and normal MAG arc welding, but also overcome the disadvantages of them. In recent years, YAG laser+MAG arc hybrid welding researches are focused on the application of high-power laser, which is several kilowatts or even tens of kilowatts. However, due to the low conversion efficiency of electric energy-laser power, and the shielding effect of laser-induced plasma is enhanced with the increase of laser power, the application of high-power laser will result in the increase of energy consumption and welding cost. Therefore, to develop the research on low-power YAG laser+MAG arc hybrid welding technology (laser power<500W), which is helpful to increase the welding efficiency and save the energy, has important theoretical and practical significance. In the paper, the hybrid welding technology, the behavior of hybrid arc and the interaction mechanism between laser and arc are investigated in the low-power YAG laser+MAG arc hybrid welding process.1. The hybrid welding technology of low-power YAG laser+MAG arc hybrid welding is investigated. The results indicate that:in hybrid welding process, the input of lower-power YAG laser is helpful to prevent the formation of undercut on the top surface of weld and make the forming at the back surface of weld continuous; For the joint of hybrid welding, the surface of weld is smooth and continuous, the deformation of joint is reduced, the tensile strength of joint is increased and the crystal grain of weld is smaller; Comparing with MAG welding, for Q235B mild steel and 0Cr18Ni9Ti stainless steel, the hybrid welding penetration depth increase of 50% and 55%respectively, the hybrid welding speed increase of 55% and 43% respectively, and the hybrid welding heat input decrease of 32% and 21%respectively.2. The arc behavior, the stability of welding process and the droplet transfer of low-power YAG laser+MAG hybrid welding process are investigated by the high speed camera. The results indicate that:the hybrid arc is attracted to the laser-heated spot and the cross-section of hybrid arc column is constricted obviously; The stabilities of hybrid arc ignition and combustion in hybrid welding process are prominent; The frequency of droplet transfer in hybrid welding process decreases. The hybrid welding current unchanges, but the hybrid welding voltage decreases. On the base of arc behavior analysis, for the contracted area of hybrid arc column, the emission spectrum is investigated by the spectrometer. The distributions of electron temperature and electron density at the contracted area of hybrid arc column, deducing respectively from the Boltzmann plot method and Stark broadening mechanism, are analyzed. The results indicate that:comparing with MAG welding, the electron temperature and density at the contracted area of hybrid arc column increase, and reach the maximum value of 1.56×104K and 1.61×1017cm-3 respectively at the position 0.9mm above laser-heated spot.3. The mechanism of low-power YAG laser accelerating the contracted area of hybrid arc column to reach the state of local thermodynamic quasi-equilibrium is investigated with the analysis of behavior of hybrid arc, distributions of electron temperature and electron density, change of hybrid welding voltage. The hybrid arc column is contracted by the effect of low-power YAG laser; Large quantity of metallic vapour induced by the YAG laser collides into the contracted area of hybrid arc column and is ionized intensively by hybrid arc; The influence of the inverse bremsstrahlung absorption effect of plasma on YAG laser at the contracted area of hybrid arc column increases. These three factors make the electron temperature increase, and also make the electric field intensity of arc decrease. Therefore, for the contracted area of hybrid arc column, the input of low-power YAG laser make the kinetic energy of thermal motion of electron increase, and also make the potential energy of arc electric field obtained by electron decrease, thus, the conditions of the contracted area of hybrid arc column are much closed to the state of local thermodynamic quasi-equilibrium. And the feasibility of applying this mechanism to the forecasts of hybrid welding penetration is verified.4. The penetration depths of low-power YAG laser welding, low-power YAG laser+arc hybrid welding under the additional electric field are investigated. The results indicate that:for Q235B mild steel, the welding penetration depth increase of 26% and 15%respectively; for AZ3 1B magnesium alloy, the welding penetration depth increase of 30% and 20%respectively. On this base, for normal laser+arc hybrid welding, a model of the influence of arc electric field on laser is set up, and the mechanism of arc electric field increasing hybrid welding penetration depth is analyzed. On the one hand, the charged particles inside the keyhole and the charged particles above the keyhole aditus move under the effect of arc electric field. Then, an impact force and a reaction force emerge inside the keyhole and at the aditus of keyhole. The forces make the molten metal at the keyhole bottom to be pushed to the wall of keyhole. Then, the laser can be transmitted downward the keyhole bottom much easily. The welding penetration depth increases due to the increase of melting efficiency of laser. On the other hand, the directional movement of the charged particles under the effect of arc electric field makes the shielding effect of plasma above the keyhole to be weakened. The welding penetration depth increases due to the increase of absorption efficiency of laser by keyhole.Key Words:YAG Laser+MAG Hybrid Welding; Spectrum; Electron Density and Temperature; Local Thermodynamic Quasi-Equilibrium; Arc Electric Field... |
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