Control strategy of twist springback for aluminium alloy hybrid thin-walled tube under mandrel-rotary draw bending

The focus of this work is to investigate the control strategy of twist springback of an industrial aluminium alloy extruded tube after mandrel-rotary draw bending, which is a complex nonlinear physical process with coupling multi-factor interactive effects. A particularly pronounced twist springback characteristic of an AA6060-T4 hybrid thin-walled bent tube was observed. It leads to difficulty at the assembly stage due to the inaccurate geometry of product. For an accurate modelling of material behaviours, a non-quadratic anisotropic yield criterion integrated with combined isotropic and kinematic hardening model was adopted to describe the strain-stress behaviours including anisotropy, Bauschinger effects and permanent softening. The corresponding mechanical tests, e.g., enhanced forward-reverse simple shear tests, were performed to identify the material parameters. By using the improved and validated finite element model, two process control strategies related to the mandrel nose placement and the axial push assistant loading are proposed for the assessment of the control efficiency. The simulation results indicate that the mandrel nose placement mainly affects the longitudinal angular springback but not twist deformation in the circumferential sections. The angular springback angle firstly increases and then decreases after several tests of forward mandrel nose placement. The other control strategy, additional axial push assistant loading with high boost, is able to reduce twist deformation, but the compensation of angular springback is not attained and even a slight increase is observed. It also leads to the rise of the of wrinkle tendency in the intrados sidewall. Finally, the wipe die rake is put forward to reduce the wrinkle tendency due to the high boost applied for twist control.