The effects of forming conditions on wrinkling in the neck of stainless-steel pipes were investigated by experiments and three-dimensional finite element simulations. The materials used in this study are pipes used for automotive exhaust parts. When the axial or radial forming pitch of the rollers is large, the outside of the pipe is subjected to considerable compressive stress in the peripheral direction by the contact with the rollers. Simultaneously, the inside of the pipe is subjected to considerable tensile stress in the peripheral direction. Thus, the pipe is subjected to excessive localized forming, which causes the curvature to become uneven in the peripheral direction, thereby resulting in wrinkling. The number of contact points with the rollers was determined. It was shown that the optimum forming conditions could be easily determined to achieve short forming times and high dimensional accuracy.
