Damage Evolution in Axial Forming of External Splines and Quenching Operation of the Tubular Gear Shafts

Monoblock tubular shafts (MTS) are manufactured using seamless hollow tubes by radial and axial forming operations. The load path of such forming operations strongly influences the damage evolution in the produced parts. Heat treatment of cold formed parts has also shown to influence the damage level or the porosity in the metal. After cold forming operations, the shafts are solution annealed and then quenched in order to harden the MTS profiles. Metallographic investigations have shown the generation of newer voids along the external contour of the gears. The current work aims at clarifying the damage evolution mechanism in the cold forming and then quenching operation and its correlation with the temperature induced phase changes. Numerical simulations were used to study the triaxiality during the forming operation. The results show the presence of a positive triaxiality along the tooth flank surface and the inner contour of the hollow shafts. Metallographic investigations and electron backscatter diffraction (EBSD) are performed to determine the individual metallic phases before and after the quenching operation. Using simulation, the effect of such thermal shock on the residual stresses and the damage evolution are investigated. Characterizing the morphology of voids and non-metallic inclusions enhances the scope of the process design, which allows manufacturing of shafts with lower damage and an increased product life of the MTS profiles.