High speed railway vehicle bogie is welded together with steel plate and tube. T joint and butt joint are the main types traditionally welded with gas metal arc welding (GMAW) method. In hybrid laser-arc welding process, laser interacts with the arc to form a stable composite welding pool, which significantly increases penetration depth. In this paper, the hybrid laser-arc welding process of S355, which is the commonly material of bogie, with 12mm thickness T joint without groove was studied. The laser optical axis and the welding wire axis were designed in different planes, and hybrid laser-arc welding parameters of the fully penetration t-joint were developed by orthogonal test. Four parameters were designed as orthogonal factors, which were welding position, laser incident angles, shielding gas flow rate, laser power. Typical defects modes and the causes were summarized, which were using as standard evaluation. The evaluation scores were obtained from the appearance and internal quality of test welds. Experiments show that welding position has the most significant influence on the forming stability of back welds; the laser incidence angle and the laser power have obvious effect on the fusion defect. The shielding gas flow rate has influence on internal and surface pore. Finishing orthogonal test, the optimized process parameters of 12mm thickness full penetration welds in T joint without groove were obtained. One-side welding with back formation was achieved soundly and stably, and the back fillet welds size was greater than a3.
Laser welding technology is widely applied in railway vehicles manufacturing, improving the appearance quality, improving the strength and reducing the weight. The outer surface of the stainless steel railway vehicle is not coated and it has high requirements on appearance quality, when the laser welding process is applied, the length of the ramping at the arc-starting position and the arc-closing position is required to ensure that there is no obvious deformation left on the outer surface. The laser welding process with different ramping length is investigated to clarify the influence of the ramping length on the deformation of the weld outer surface, to optimize the ramping length in the process. The comparison tests of different ramping lengths were carried out. The surface deformation, residual stress and tensile strength of different ramping length joints were compared, and the influence of the length of ramping on the deformation of the welding seam is analysed comprehensively. And with the increase of the length of ramping, the deformation of the welding seam decreases. There is no obvious influence on the weld arc position when we choose the ramping length from 3 - 5 mm, with the maximum deformation at the weld arc position about 100 μm.