Press Hardening of Tubes by Hot Metal Gas forming - Validation of new materials

One field in the work of the Fraunhofer Institute for Machine Tools and Forming Technology IWU in Chemnitz is industry applied research in hot metal gas forming, combined with hot stamping in one process step.The linked process offers great potential for lightweight construction because material- and structure-lightweight technologies are combined.In this paper the results of investigations on new hot stamping steels from SSAB AB (Docol 1800 Bor and Docol 2000 Bor) are presented.Hot tensile tests recorded by the project partner (University of West Bohemia, Faculty of Mechanical Engineering) were used to create a material model for thermos-mechanical forming simulations. The provided raw data was translated into curves of the real stress and real strain of the two materials. Each of the material models consists of approximated flow curves for 7 forming temperatures and 4 strain rates. All 28 flow curve approximations were integrated in a LS-DNYA material model for hot metal gas forming simulation.Preliminary tests were carried out using a tool to permit evaluation of the forming behavior of Docol 1800 Bor and Docol 2000 Bor tubing. These tests were used to validate the material model. Using this geometry, the intention was to perform a series of tests with different furnace temperatures, maximum internal pressures and pressure development rates to evaluate the formability of Docol 1800 Bor and Docol 2000 Bor. The wall thickness, hardness and microstructure of selected components were investigated for the evaluation. The tests were carried out using the completely modernized Dunkes/AP&T HS3-1500 hydroforming press at the Fraunhofer IWU.In summary, the material modeling and the forming simulation was successfully established. The simulation results have a high correlation with the experimental data regarding the thinning.The forming of the demonstrator geometry was successful and different hardness values could be achieved depending on the furnace temperatures and the material. Strengths up to 645 HV could be measured on the component with a complete martensitic structure.