Forming of thin-walled hollow spheres using sacrificial polymer mandrels

This paper introduces a novel type of mandrels (sacrificial polymer mandrels) that is expected to enlarge the tube forming window of very slender preforms by diminishing the risk of wrinkling and plastic instability. The overall feasibility of the concept is demonstrated by means of a pre-industrial test case consisting of single-stage nosing of hollow spheres for gas storage applications.Numerical modelling based on independently determined mechanical properties of the materials and executed on an innovative extension of the finite element flow formulation for metal–polymer cold forming applications is performed with the purpose of identifying the most important process parameters and understanding their influence in the overall formability.Results show the adequacy of using sacrificial polymer mandrels for the small-batch and low-cost production of thin-walled hollow spheres and, because the novel type of mandrels can easily be extended to other tube forming operations, it effectively contributes to transferable technological knowledge.