Optimizing blank geometry for die-less hydroforming of spherical parts

Spherical metal shell constructions are widely utilized as storage containers in the chemical industry or as characteristic symbols in large urban centers. Traditional manufacturing methods for these shells typically involve deep drawing or spinning hemispherical halves, which are subsequently welded together. These conventional methods suffer from low productivity and limited economic viability due to the requirement for large dies and machinery. In contrast, spherical metal parts produced using Die-less HydroForming (DHF) offer high dimensional accuracy, reduced costs, and shortened production times compared to traditional technologies. The DHF process entails defining the blank profile, initial bending formation, sealing the blank profile by welding, and applying increasing fluid pressure to deform the outer shell. The determination of the initial blank shape is crucial as it significantly impacts product quality. Initial blanks for fabricating spherical parts using DHF can take various forms, but are primarily categorized into two development types: meridional and latitudinal. Despite extensive research on the initial blank structure for forming spherical metal products, a critical gap remains: the lack of comparative studies on the post-forming product quality of different blank types. This paper directly addresses this void, employing numerical simulation and experimental validation to comprehensively assess how these two initial blank types influence product quality, specifically by analyzing thickness variation and dimensional accuracy. Spherical metal products with a diameter of 400 mm, made from SUS304 stainless steel, were used for comparing post-forming quality. The research results indicate that latitudinal blanks achieve a dimensional accuracy deviation of 2.3%, an average thinning rate of 9%, and a shorter weld seam length, thereby reducing manufacturing time and enhancing productivity.