Hybrid laser-arc welding process of full penetration T joint in high speed railway vehicle bogie

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.