Wrinkling and instability analysis of thin-wall cylindrical parts in viscous medium outer pressure necking

Due to the influence of stability of cylindrical parts, necking process is subject to wrinkling and instability, and it is difficult to form parts with large necking scales. In this paper, a novel method of forming thin-wall special-shaped curved surface cylindrical parts with large diameter variation is proposed by using viscous medium outer pressure necking process. The wrinkling and instability processes of specimen with constrained and free ends are analyzed by experiments and finite element method, and the variation principles of geometrical shapes and stresses are studied. Results show that fixing the end conditions can improve the stress distribution of instable and wrinkling specimen and is benefitial to the elimination of wrinkles. Under the condition of high viscous medium pressure, the part with diametrical reduction of 15% can be formed directly.