A new approach to evaluate bending forces for deep-drawing operations of a TRIP700 +EBT steel sheet

In this work, a new approach was developed to determine the bending, unbending and friction forces involved in deep-drawing processes of metallic sheets based on a sheet drawing-bending test. The procedure used both the experimental and deduced behavior of sheets in bending and unbending processes under tension. To obtain experimental data, a new apparatus was built to measure the reactions forces in the bending tool. These tests were applied to a TRIP700 +EBT steel sheet in diverse pure shear deformation states, with two different lubricants. The effect of the back tension and the state of the material were also studied by bending and unbending processes using tensile tests under diverse pure-shear conditions. Deduced forces, like bending and unbending forces, were determined by introducing these experimental data into an expressly created numerical method. The obtained results allowed us to state that the TRIP700 +EBT steels sheet displayed evolutional mechanical behavior since the induced martensite phase transformation effect depended on the deformation mode and intensity, had good formability and a low friction coefficient with steel tools, which was almost constant and independent of the pressure in the bending tool.