Effect Of friction on wrinkling in Nc bending of tubes with larger size factors

With size factors (SF) larger and bending factors smaller, the wrinkling in NC bending of large size tubes has become a key to be solved for improving the bending limit and forming quality. The friction parameter and size factors are the key factors to affect the wrinkling. In the present paper, a numerical-analytical method combining the energy criterion with the elastic-plastic FEA is used for the wrinkling prediction, and the method has been verified by the experimental result. And then, the effects of SF and friction on the wrinkling are revealed in the forming process and the results show: (1) The larger the size factors, the larger the maximum tangent compression stress boundary, the wrinkling possibility and the roles of the friction. (2) For the large size tubes (D/t>80), the smaller the friction of bending die, the larger the wrinkling and the earlier the most possible wrinkling time. The larger friction between mandrel or wiper die and tube, the smaller the wrinkling; the larger friction between pressure die and tube, the larger the wrinkling.