| The automatic welding equipment is backward and the advanced and efficient welding technology is insufficient for the ship construction in our country, which has become the bottleneck restricting the development of China’s shipbuilding industry. At present, the research of high-efficient welding technology is mainly focused on the butt weld, not the fillet weld. However, the T-joint is the main joint type in the ship welding while the traditional electric arc welding can produce the defects such as serious splashing, insufficient welding foot and undercut. So in the basis of previous study in our laboratory, the laser-MAG hybrid welding is utilized in the high-efficiency welding of T-type structures. The law of fillet weld formation is studied by welding procedure, and the microstructure and mechanical properties of the welded joint are analyzed. Then the application of welding procedure is demonstrated.Firstly, it is found that the laser can attract and compress the arc, stable welding process, and reduce the spatter by the research of arc shape and weld forming in the laser-MAG hybrid welding on the plate surface. At the same time, the addition of laser increases the heat input of welding, stirs the molten pool, promotes the spreading of weld metal in the base metal, increases the penetration depth and inhibits the generation of undercut defects in high speed welding. Then by the comparison of the welding technologies of T-joint between MAG welding, double wire MAG welding and laser-MAG hybrid welding, it is found that without increasing the welding current, the hybrid welding with 1.5 kW laser can make the critical welding speed of undercut increase about 100% than single wire MAG welding. The influence of main parameters of hybrid welding on the forming quality of the fillet weld is analyzed in detail. It is found the Dla, welding current and welding torch inclination angle have remarkable influence on the undercut of baseplate of fillet weld while the wire offset is the main process parameter to effect the undercut of ribbed plate. Under the condition of this experiment, the Dla of 1～2 mm, wire offset of 2 mm, welding torch inclination angle of 45°～50°, welding current of 330～340 A and the laser power of 1.5 kW can reduce the tendency of undercut in the baseplate and ribbed plate of fillet weld, and also improve the welding speed.The observation of microstructure and the test of micro hardness show that compared with MAG welding, the microstructure of T-joint of laser-MAG hybrid welding is refined and the micro hardness is higher. The mechanical property test show that the difference of tensile strength between the two is small. But when the baseplate is stretched, the plastic deformation ability of hybrid welding joint is stronger than the MAG welding joint with undercut and the plasticity is better. The effect of the slight undercut of the baseplate on the fatigue of the ribbed plate is notable, but on the fatigue of the baseplate is little. So in the aspect of the fatigue of the plate, the T-joint of laser-MAG hybrid welding has obvious advantage. At the same time, in the aspect of impact performance, the laser -MAG hybrid welding joint also performs well and the impact work of the joint reaches 91.5% of the base metal.Finally, the improved laser-MAG hybrid automatic welding system is demonstrated and applied in shipbuilding enterprises. By integrating laser-arc hybrid welding technology, seam tracking and recognition technology and robot automatic control system into a whole, the hybrid automatic welding system obtains a good curve of the curved face and the shape of the fillet weld in the welding speed of 1-1.5 m/min. |
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