Investigation of the hydroforming of spherical vessels from a new type of flat polyhedral shell

Abstract The technology of the die-less hydroforming of spherical vessels from a new type of flat polyhedral shell (combination frustum shell) is advanced and the forming process is researched by means of the elastoplastic finite-element method and experimentation. The research results show that the new technology is feasible not only in theory but also in practice. Inner concave deformation and wavy line deformation occur near to the weld seams or crest lines (the latter are the intersection lines of two petals and may be a weld seam or just a straight line formed by the bent petals). Severe deformation takes place on the horizontal weld seams, with less deformation on the vertical weld seams. High tensile stress normal to the weld seams exists on the inner surface near to the weld seams. Proper shell structure design should ensure the successful forming of the spherical shells. The number of the frustum bands and the side number of the polar blanks should be selected properly to ensure that the minimum dihedral angle is greater than 135° and the horizontal angular weld seams where severe deformation occurs should be replaced by crst lines in the roll-bent blanks.