Laser-TIG (tungsten inert gas) hybrid welding process is applied to produce stable back beads in the first layer during one-side multilayer welding. To explain why stable back beads can be formed, a comparison is conducted between single TIG and laser-TIG hybrid welding. Results indicate that during laser action the arc column is enhanced and deflected to the keyhole, which changes the spatial distribution of plasma by strong attraction. The keyhole plasma possesses extreme electric conductivity. After laser action, the enhanced arc is restituted, the low energy density arc acts on the molten pool, and the bottom of the molten pool is solidified to prevent its collapse. The heat and force are redistributed over the top of molten pool under the alternative action of the enhanced arc and original arc. In this case the thermal distribution and mechanical situation in the molten pool must be more balanced and reasonable, and the back bead appearance is continuous, stable and uniform. This process gives high quality and efficient root welding of the thick plate.
A series of laser-tungsten inert gas hybrid welding with filler wire experiments were performed on the TA15 titanium alloys to investigate the effect of welding parameters, such as the distance between the axis of the laser beam and the tip of the tungsten electrode (Dla), the defocused distance of the laser beam, and its CO2 concentration in the shielding gas, on the weld appearance and dimension. The mechanism of the weld formation was then analyzed. The results demonstrated that by adjusting space position between the heat sources and protecting the shielding gas content, the undercut defect could be suppressed effectively in the hybrid welding process. With the increase in the Dla, defocused distance, and CO2 concentration, the width of the top weld presented an increasing trend, while the width and reinforcement of the backside showed a decreasing trend. The ridgelike appearance may be effectively suppressed if the Dla, defocused distance of the laser beam, and CO2 concentration in the argon shielding gas were more than 2 mm, 4 mm, and 2%, respectively, because the Dla, defocused distance, and CO2-determined energy concentration, surface tension, and Marangoni convection determine the molten metal flow direction.
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