Numerical-experimental analysis of thin magnesium alloy stripes subjected to stretch-bending

The present work aims at studying the combined effect of tangential bending and stretching stress (quite common in the stamping process, e.g. in the pinch or die shoulder regions) on thin magnesium (Mg) sheets when working at elevated temperature. An experimental/numerical approach was adopted using specific equipment able to heat the sheet only in the bending region and to stretch the sheet after the wiping process. Stretch-bending tests were aimed at understanding the process parameters really affecting the stretch-bending process at elevated temperature using the design of experiment (DOE) technique. In particular the temperature, the punch speed, the bending radius and the rolling direction were considered in the screening analysis. Beside the maximum stretching load, also the springback phenomenon was measured, in order to quantify the amount of plastic strain in the bending section when changing the process parameters. The finite element (FE) analysis was focused on the process parameters which resulted to play a key role: the bending radius and the temperature. Plastic strain distributions in the bending area and the critical condition occurrence in the stretching step were evaluated using 2D fully coupled thermo-mechanical models.