Study On Technologies Of Laser-arc Hybrid Welding For Structural Steel Plates

The bogie frame is one of important components for railway vehicles, the mostof which are welded box beam structures with medium and thick plates. At present,Changchun Railway Vehicles Co., Ltd. mainly adopts automatic and semi-automaticGMAW to product bogie frames. They have low production costs and mature weldingprocess, but the main problems present are: long welding preparatory work, cleanupwork before welding, such as grinding, takes plenty of time, which result in lowproductivity; multi-weld seams，large amount of heat input，complex residual stressand obvious welding deformation lead to safety hazard to some degree; what’s more,welding and grinding produce large amounts of dust and harmful gases, which canpollute the environment seriously. Laser-arc hybrid welding is an efficient andhigh-quality welding method. It use laser and arc as the dual heat sources with largedepth of penetration, low heat input, fast welding speed and gap adaptable hotspot, theproduction of framework welding problems can be effectively solved, particularly forthe welding of medium and thick plates.In this paper, by using laser-arc hybrid welding technology, different processesof welding are adopted to weld10mm,12mm and16mm thick low alloy high strengthsteel (S355J2W) butt joints and T-joints. By changing the laser power, arc current,welding speed and welding layers, the influence factors of appearance of weld andweld quality are found, and finally certain welding parameters are taken. Adoptingthree weld layers process can get an ideal weld shape and more perfect welded joints:weld penetration completely, no weld defects such as filling and undercut.Macroscopic views of the laser-arc hybrid multilayer welded joints are observed byan optical microscope, we compared the different zone characteristics, the features ofmicrostructure of the weld zone after several thermal cycles and the cause forvulnerable spot of the lower part of weld joint, which as a result of the opposite graingrowth during solidification of molten pool owing to the small size of weld. Hardnesstest on laser-arc hybrid welding joint is conducted: the hardest area is theheat-affected zone, followed by the weld zone, which are both higher than the base metal; lower part is harder than the upper part of the weld. After a side bend of180°for the joint, the tiny crack appears in some samples and the cause of crack and theposition of micro-cracks theoretically analyzed in the paper. Impact tests the basemetal and welded joint t different temperatures show that the stable impact toughnessof base metal and the impact toughness of the weld seam are lower than the basemetal, and we analyze the impact fracture morphology, and explain the reasons ofductile fracture and cleavage fracture at the mouth of the crack. In addition, we alsoanalyze the second phase particles of base metal. By fatigue test, the fatigueperformance of laser-arc hybrid welded joint is provided, and the appearance reasonsand propagation rules of crack is analyzed, combined with the fracture morphology.