Experimental research on reconditioning transmission axles by MAG robotic welding

The current paper presents the experimental program conducted in order to determine the welding technology for shaft bond wheels, of Cr and Ni low alloyed steel, in enhanced condition. The material that makes up the shaft bond wheel is in laminated state, with a diameter of 70 mm and a high tendency to cracks when subjected to welding. During exploitation, these axles are subjected to stress and fatigue which imposes developing materials with equal resistance as well as avoiding concentrators in the joint design. The steel transmission shafts, butt welded together, contain Fe-1.7%Cr-2%Ni type with a 0.4%C, respectively Fe-0.7%Mn-1%Cr type with 0.3%C, with hardness approx. 250HB on the shaft and 350HB on the axle. The preheating and inter-pass temperature, combined with mechanical characteristics of welded joints, that have similar resistance, was performed according to SR EN 1011-2-2004, using the help of equivalent carbon computational relations. Fractometric analysis of deficiency areas extracted from parts used in exploitation, at the beneficiary exploitation site, due to defects, highlighted "fish eye" defects, fatigue cracks, that determined choosing this welding technology, namely robotic, in protective gas environment, Corgon 18 – 82%Ar and 18%CO2, using EN ISO 16834-A G694MMn3Ni1CrMo wire with a diameter of Φ1.6 mm. Welding was performed by maintaining 150°C temperature between layers, at a welding speed of 280 mm/min, power 200±10A, wire feed speed 3.7 m/min, in protective gas, Corgon 18 with a 18.22 l/min flow. The joint was designed so it will have minimum concentration areas and assure cooling of welded zones, after the joint was completely filled. After the repair we extracted samples from the joint, in order to test the weld quality and assimilate the technology. Metallographic and compositional analysis performed on specific areas highlighted improved structures in the center of the weld – zone 2, which ensures a proper tenacity of the joint and a hard coat, at the exterior, that favors the good operation of the assembly under critical fatigue conditions. Results obtained confirm and recommend implementing the developed welding technology into industrial environment.