Analytical modeling of wall thinning during corner filling in structural tube hydroforming

In a tube hydroforming process, an internal pressure is used to expand a circular tube into one with non-circular sections. Friction at the material/die interface plays an important role in determining the distribution of the thickness during deformation. In this paper, an analytical model is developed to determine the variation in the stresses and strains along the tube wall as the internal pressure increases to expand the circular tube into a square cross-section. Based on the analytical model, a parametric study is conducted on the effects of the coefficient of friction and the material properties on the distribution of cross-section thickness in the hydroformed tubes. Such parametric study is useful in establishing guidelines for designing the structural tube hydroforming process. It also helps in the search for limits of the process capabilities. One of the strengths of analytical modeling is that it gives more insights into the mechanism through which friction affects the deformation during tube hydroforming.