Study Of Technique And Mechanism On Hybrid CO₂ Laser-TIG Welding

Laser-arc hybrid welding is a new welding technology, which combines the heating sources of both laser beam and the arc on the same molten pool synchronously. The hybrid welding technique holds the advantages of the laser beam and electric arc, which makes it become a new efficiency welding technique.Based on summarization of the current research on hybrid welding technique, some systematic experimental work was undertaken to study the effect of the hybrid laser–TIG welding process on the bead quality in this paper. Firstly, a paraxial CO₂laser–TIG hybrid welding system was set up by Rofin Sinar 5kW CO₂ laser and Miller TIG welding machine, and a series of bead–on–plate experiments were carried out on the 316L stainless steel sheets with 3mm thickness. The welding bead shapes were characterized by microscope. The experimental results demonstrated that the laser–TIG hybrid welding can increase penetration & width and improve the quality of weld bead formation when the optimum processing parameters were chosen.The effects of various processing parameters such as laser power, arc current and the distance between the laser beam spot and electric arc spot on the welding shape were studied in detail. It was found that under stated conditions the weld penetration depth mainly depends upon the laser power and the bead width mainly depends upon the arc power. When the laser power is above 2.5kW, there will generate a"key hole"effect in 316L plates, which will enhance the effect of the hybrid heating sources and affect the weld penetration depth greatly;On the other hand, the bead width is closely relative to laser power and the electric arc energy when the arc current is less than 150A. when the arc current is more than 150A, however, the bead width is determined by the energy of the arc only. There exists an optimal laser-arc distance (2--3mm), with which the weld bead penetration depths can be improved to 1.46--2.54 times.Based on the research results above mentioned,the relationship between the gas concentration & shielding method and the process stability of CO₂ laser-TIG (Tungsten inert gas) hybrid welding is studied in detail. In this paper, the interaction of laser beam with electric arc was studied by the plasma images,the optical photos of the cross-sectional and the bead penetration depths & widths. The results show that the gas of coaxial nozzle can compress the plasma, which increase the welding penetration depths effectively. Otherwise the expanded plasma will absorb too much laser energy and result in unstable hybrid process with distorted electric arc.Finally, following conclusions can be drawn up from above experimental results: the welding penetration depth can only be enhanced under the appropriate shielding gas method, and the effect of shielding gas methods on the interaction extent between laser plasma and arc plasma is the main factor for efficient synergetic effect. The pure torch method can not generate the efficient synergetic effects, and the hybrid protecting method by torch plus paraxial nozzle method has only a narrow parameter range for getting the efficient synergetic effects, while the hybrid protecting method by torch plus coaxial nozzle method can ensure the efficient synergetic effects under a considerable wide parameter range.