3D numerical study on wrinkling characteristics in NC bending of aluminum alloy thin-walled tubes with large diameters under multi-die constraints

With an increase in the diameters of aluminum alloy thin-walled tubes (AATTs) and a decrease in their bending radii, wrinkling characteristics and its prediction under multi-die constraints have become a key problem urgently to be solved for improving the forming quality in numerical control (NC) bending of AATTs with large diameters. Thus in this paper, considering the characteristics of the bending processes, based on the ABAQUS software environment, a 3D elastic-plastic finite element model and a wrinkling energy prediction model under multi-die constraints are established and their reliabilities are validated, respectively, in which, the appropriate choosing of forming parameters is achieved to guarantee no excessive thinning and flattening in the processes even if wrinkling borders on occurring. By combining the two models, variation relationships of the maximum wrinkling factor with different compressed deformation zones and forming ratios, and effects of clearances and friction between different dies and tubes on the maximum wrinkling factor are obtained, and then an investigation into the wrinkling characteristics is carried out for the processes. It is found that the larger the diameters of AATTs, the larger the wrinkling sensitive zones (WSZs), and there is a larger possibility of wrinkling in the bending segments of WSZs than in the straight ones; the larger the effects of clearances and friction between different dies and tubes on wrinkling.