An Analytical Study of Allowable Pressure in Hydroforming of Metal Bellows

There are many industrial applications, such as in aerospace, nuclear and petrochemical industries, that involve using metal bellows. Tube hydroforming is the major process by which the metal bellows are produced. Although many parameters may affect the final product, the fluid pressure can be regarded as the most important parameter in hydroforming a metal bellows. Low pressure may result in some defects such as wrinkling. On the other hand a high pressure may lead to a highly thinning and even rupture. In the previous researches, no theoretical criterion has been proposed to predict the allowable forming pressure. In this paper, an analytical equation is proposed for determining the allowable pressure, based on thin-walled cylindrical vessels. Neglecting the elastic deformation, Swift equation along with von-misses yield criterion was used to model tube deformation. The analytically computed pressure compared with the existing experimental results and a close agreement was observed. This evidently shows the validity of the propose model.