Modelling of wrinkling in NC bending of thin-walled tubes with large diameters under multi-die constraints using hybrid method

Numerical control thin-walled tube bending is an advanced technology for manufacturing precision bent tube parts in aerospace, aviation and automobiles, etc. With an increase in the diameters of thin-walled Al-alloy tubes and a decrease in bending radii, accurate prediction of wrinkling instability under multi-die constraints is still one challenge and a focused issue, especially for the thin-walled Al-alloy tubes in aviation. Solely using pure analytical solution method, energy-based analytical solution method, pure explicit algorithm or implicit algorithm cannot accurately predict the wrinkling instability. In this study, the analytical bifurcation solution, analytical-numerical energy-based model and eigenvalue buckling analysis are conducted to generate different kinds of buckling modes, respectively, and a series of imperfections are defined in the shapes of these buckling modes. Second, by assigning the geometrical imperfection into the perfect mesh of the tube, a series of hybrid explicit FE models for numerical control rotary-draw-bending is established. The numerical perturbation analyses are carried out with different bifurcation modes-shapes. Thus, based on the minimum energy principle, the shape of imperfection (bifurcation path) and the magnitude of the imperfection (scaling factors) are chosen, which is corresponded to the lowest level of energy consumption. Third, a set of bending experiments is conducted on Al-alloy tube to verify the predictive capability. The predicted results are in good agreement with the experimental results.