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 thinwalled 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 thinwalled 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 spining,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.

Effects of spinning parameters on microstructures of ellipsoidal heads during marginal-restraint mandrel-free spinning

Marginal-restraint mandrel-free spinning is an advanced technology for manufacturing ellipsoidal heads with large diameter-thickness ratios.The effects of spinning parameters on the forming accuracy of ellipsoidal heads have been studied,and optimized spinning parameters have been obtained.The microstructure evolution of a workpiece is usually very complicated in the spinning process.In this work,the influence of spinning parameters on the microstructures of two-pass spun ellipsoidal heads is studied.It is found that the forming angle and feed rate of the first pass,angle between passes,and feed rate of the second pass significantly affect the microstructures.Meanwhile,the evolution rule of the microstructures near the inner and outer surfaces of the spun parts is almost consistent.A large forming angle,large angle between passes,or large feed rate of the second pass are beneficial to obtain uniform microstructures.A small or large feed rate of the first pass reduces the microstructure uniformity.To improve the microstructure uniformity between the inner and outer surfaces,the optimized spinning parameters are determined.