Increasing the Occurring Normal Stresses in Conical Tube-Upsetting Test Using Adapted Specimen Geometries

Friction is part of almost any forming process, thus, friction modelling is mandatory for process modelling. Since frictional stresses are difficult to measure, typically laboratory experiments are used, where a dimension sensitive to frictional stresses is measured instead. The conical tube-upsetting test, an advancement of ring compression test, is such a laboratory experiment. Here, the change in geometry is measured to inversely determine friction parameters. The process parameters, such as temperatures, strain rate and contact pressure should be as close as possible to the forming process that is modelled with the laboratory experiment. Especially in hot bulk metal forming, normal stresses greater than yield stress of the work piece can occur, which has significant influence on the frictional conditions. However, previous work has shown that normal stresses in conical tube-upsetting test are lesser than the yield stress of the workpiece material, which restricts the experiments application regarding hot bulk metal forming. Thus, in this work the specimen geometry of conical tube-upsetting test is investigated by means of FE-simulations with respect to the occurring normal stresses between workpiece and die. Additionally, the influence of altered geometries regarding the sensitivity towards occurring friction is taken into account. The results suggest that especially an increased thickness of the specimen in the bottom area leads to greater normal stresses. At the same time however, the sensitivity towards friction conditions decreases.