Study Of Laser-Arc Hybrid Welding And The Magnetic Properties Of Laser Welded Super-Low Carbon Steel

Laser-arc hybrid welding is a new developing welding technology, which combines the high power density of lasers with the cheapness and high efficiency of the arc welding to achieve deeper welding penetration and good adaptability. Laser-Arc hybrid welding technology has been well developed abroad, but is still at the stage of fundamental research in our country. In this paper, we aim to the researches on the laser-arc hybrid welding arts and the interaction of laser beam with arc plasma.In our experiments, a TIG arc welding apparatus was chosen for combination with a CO2 laser, and Q235 steel sheets with 3~5mm in thickness were used as welding materials. Besides, the welding conditions at different parameters were studied systematically. The experimental results indicate that the introduced TIG arc obviously helps to increase the welding penetration and welding fusion extent. The arc current and relative position between laser beam and arc are two main influence factors in hybrid welding process. Maximum welding penetration can be gotten when arc current matches with the laser power properly. Over-high arc current will decrease the welding penetration for the absorption and shielding on laser energy by the arc. Accordingly, when laser power varies in the range of 2750W~4000W, the corresponding matched arc current ranges in 80A ~160A. Especially, the hardness of the welding seam by laser-arc hybrid welding is basically lower and more uniform than that by laser welding.In this paper, the interaction of laser beam with arc was studied, and the effect of laser beam on compressing or expanding the TIG arc was also investigated. The research results show that the compressed arc can increase the welding penetration effectively, while the expanded arc will absorbing too much laser energy and result in unstable hybrid process with distort arc. Furthermore, the absorption and shielding mechanism of laser by arc plasma was discussed. Traditionally, kinescope bracket is made of super-low carbon steel and manufactured by the use of whole punching method, which causes great waste of material. It is an effective way to reduce material waste and production cost by punching the jointed L-shape sheets. Resistance welding method has great destroy to the magnetic property of the seam, which will cause image distortion of the display when swerving, and post heat treatments are needed. In our experiments, laser welding is used to replace the resistance welding to weld the L-shape steel sheets, and the microstructure and magnetic property of the seam are compared. The results show that the magnetic property of the seam depends on the structure distortion that caused by different welding methods. As the resistance welding is concerned, the microstructure of seams exists great distortion for its large heat input, which makes the coercivity (Hc) and the remained magnetization (Mr) both increase, and thus blocks the remagnetization of the display when swerving. As far as the laser welding is concerned, the microstructure distortion of the seam is very small for much lower heat input and the grains of the seam is very close to that of the starting materials, which influences the coercivity (Hc) and the remained magnetization (Mr) little. Hence, workpieces welded by laser welding can get good display even though without any post heat treatment.