Integral hydro-bulge forming of pressure vessel heads

Abstract

A new process has been proposed to form pressure vessel heads by hydro-bulging circular flat plates as an alternative to traditional processes. This new process is especially intended for the manufacture of pressure vessel heads of very large diameter that may not be possible to form by traditional processes, and also for products of various sizes or very small production batches. A pressure vessel head usually includes two parts: a central elliptical plate and a circular skirt. The skirt may be formed by traditional processes (press forming), whilst the central elliptical plate may be formed by hydro-bulge forming, the vessel head being manufactured by welding these two parts together. Experiments have been carried out to investigate this process, and it has proven feasible to hydroform the central elliptical plates in pairs with a fixed boundary. The explicit non-linear FE code LS-DYNA3D is used to simulate two different process schemes: free hydro-bulge forming and hydro-bulge forming with a fixed boundary. The wrinkling occurring during free hydro-bulge forming is predicted and analyzed. The simulation of the model with a fixed boundary gives results in good agreement with experimental results, thus this process is proven feasible. The simulation also shows that a thickness-enhanced ring boundary can improve product quality.