Fundamentals and application of tube hydro-forming

The failure modes during the hydro-forming process are analyzed, the wrinkling criterion and its affecting factors are given by the elastoplastic theory. The optimal loading paths are discussed, and the control of wrinkles are numerically simulated. The experimental results of aluminum and stainless steel tube hydro-forming conducted in the first set hydro-forming press in China are introduced. The research results show that the critical axial force for wrinkling is gradually increased with the increase of internal pressure. The loading parameter λ=1.0,i.e., the tube is in the pure shear state, can lead to the optimal loading path. This optimal loading path can avoid the occurrence of wrinkling and make the thickness unchangeable. The real loading path should be controlled close to this optimal loading path. It is pointed out that not all wrinkles are defects and the beneficial wrinkles can be used to reduce the thinning.