Marginal-restraint mandrel-free spinning process for thin-walled ellipsoidal heads

Metal sheet spinning is an advanced near-net forming technology for the manufacture of thin-walled ellipsoidal heads. The exact control of dimensional accuracy, however, is a considerable problem for spinning thin-walled parts with large diameter-to-thickness ratios. In this work, a marginal-restraint mandrel-free spinning process with two passes is proposed for the fabrication of thin-walled ellipsoidal heads without wrinkling. A finite element model is established and verified to study the influences of spinning parameters on the dimensional precision of thin-walled ellipsoidal heads. It is found that the spinning parameters considerably influence the deviations of wall thickness and contour characteristics. A small forming angle or small roller fillet radius during the first pass spinning, as well as the small angle between passes or high feed ratio during the second pass spinning, can improve the wall thickness precision. Meanwhile, as the forming angle or feed ratio is increased during the first pass spinning, the contour precision initially increases and then decreases. During the second pass spinning, the contour precision can be improved at a small angle between passes, whereas it deteriorates at a larger roller installation angle. The optimized spinning parameters are obtained and verified by experiments.