Computational and experimental modeling of stretch forming operations

Selected results from a study of the stretch forming process are reported. Sheet materials with a wide range of mechanical properties have been tested, including a carbon steel, 70/30 brass, 18/8 stainless steel, and an Al--Mg alloy. A comprehensive comparison of numerical simulations with experimental results shows quantitative agreement for important process factors such as strain distributions and punch force. The parameter variation study demonstrates considerable influence of the material parameters and the friction coefficient on the results. The strain distributions are found to be most sensitive to parameter variations. The experiments were performed with a cylindrical punch and a firmly clamped blank. The sheet was lubricated with various oils. Strains were measured with an etched grid. The numerical calculations were based on a finite element procedure developed for simulation of arbitrarily shaped 3-D forming operations. The emphasis was put on the proper description of large strain and large rotation plasticity. Relatively simple hardening and friction models used appear to be satisfactory and require reasonable computational time. The elastic--plastic description, with Hill's anisotropic model, was used. This allowed for elastic effects, unloading, and multistage process. Graphs. 22 ref.--AA(UK/US).