Experimental and numerical prediction of springback and side wall curl in U-bendings of anisotropic sheet metals

Springback is a common phenomenon in sheet metal forming, caused by the elastic redistribution of the internal stresses during unloading. It has been recognised that springback is essential for the design of tools used in sheet metal forming operations. A finite element (FE) program has been used to analyse the sheet metals axisymmetric U-bending process. The underlying formulation is based on Lagrangian elastoplastic materials model. Normal anisotropic material behaviour has been considered. A contact algorithm for arbitrarily shaped rigid tools has been realised by means of penalty approach. The interaction of sliding surfaces is modelled with a modified Coulomb friction law. This paper describes a robust method of predicting springback and side wall curls in 2D operations under plane strain stretching, bending and unbending deformations. Also the effect of tool geometry and blankholder force on the final shape after springback are discussed. The accuracy of the model is verified by comparison with FE of MARC package and experimental results.