Simulation of axisymmetric sheet forming tests

Improvements in engine performance result in a continuing increase in the operating temperatures of automotive exhaust systems. Presently, most exhaust components are fabricated from Type 409, a 12 wt.% chromium ferritic stainless steel. In order to meet durability requirements, some components are fabricated using ferritic stainless steels with higher chromium contents. While these alloys have improved oxidation resistance, they are generally less formable than Type 409. As a result, simulation techniques become an important tool that can be used to understand and accommodate for the formability behavior of these alloys. In any simulation technique, verification of its accuracy is first required. To accomplish this mechanical testing was used to develop the constitutive equations for four stainless steel alloys: AK STEEL® 409, AK STEEL® 304, AK STEEL® 18CrCb and NITRONIC® 30. Friction coefficients were also measured using the drawbead simulator (DBS) test. Axisymmetric simulations were carried out for two standard forming tests, the Olsen cup stretch test and Swift cup-drawing test, using SHEET-S, a two-dimensional finite element program. Experiments were performed to assess the accuracy of these simulations. The comparisons show good agreement in both the strain distributions and predicted punch-failure heights; the latter based on use of a simple failure criterion.