Investigating spring back phenomena in double curved sheet metals forming

Spring back is one of the main reasons for geometrical inaccuracy of stamping products. Many successful attempts have been done to calculate the amount of spring back of sheet metals, but most of them belong to the simple cases such as single curved U or V bending. In this paper an analytical formulation based on the moment–curvature relationships considering sheet thickness changes is presented for predicting spring-back in double curved sheet metal forming process. In this formulation displacement of neutral surface is also considered. The accuracy of the formulations is verified by comparisons with finite element and experimental results. The effects of some geometrical parameters such as thickness and curvatures radius on the spring back behavior of sheet metal have been investigated. Different sheet metals have been examined for modeling and experiments including SPCC steel sheets, commercial pure titanium sheets and cartridge brass sheets.