Deformation behavior of convolute thin-walled AA6061-T6 rectangular tubes manufactured by the free bending forming technology

During manufacturing thin-walled tubes using free bending forming (FBF) technology, defects such as wrinkling, cracking, and cross-section distortion are easy to exist due to various forming parameters' direct and indirect influence, which seriously influences the forming quality of the rectangular tubes. Thus, in this study, the finite element (FE) modeling of thin-walled AA6061-T6 rectangular tubes manufactured by FBF technology was accomplished and verified through experimentation. Moreover, the influence of different parameters on the deformation behavior of the rectangular tubes was systematically investigated using FE modeling. The results showed that the maximum thickness changing rate and the cross-section distortion appeared once the bending die moved to the maximum eccentricity (U_max). Besides, with the increase of yield strength-Young's modulus ratio (σ_s/E), thickness (t₀), fillet radius (R_f), clearance (Δc), friction coefficient (f), and chamfer radius of the guider (R_c), the thickness changing rate and the cross-section distortion decrease, while the bending radius enlarges simultaneously when the parameters are set within reasonable limits. Unlike the above parameters, with the improvement of the axial feeding speed (V_f), the thickness changing rate declines while the fluctuation of bending radius is not significant. Under the joint action of the axial force P_L, the structural characterization of the rectangular tube and the dies of constraints, the thinning of the outer wall and the web distortion are inhibited, and the variation amplitude of them is much smaller than that of thickening of the inner wall and flange distortion during the free bending process.