2D springback and twisting after drawing of copper alloy sheets

This study deals with forming and springback of U-shaped channels made of copper alloy thin sheets. Three materials are considered: pure Cu, copper-beryllium CuBe2 and copper-iron CuFe2P alloys. All these materials are supplied under sheets of thickness around 0.1mm. Their mechanical behavior is investigated in monotonic uniaxial tension, loading-unloading sequences in tension and simple shear, in order to highlight the hardening, the evolution of the unloading slope with plastic strain and the magnitude of Bauschinger's effect. Then, drawing of U-shaped elongated parts is performed; to enhance 3D springback, a misalignment of the blank with respect to the punch, die and blank-holder is deliberately applied. The geometry after tool removal is measured by laser scanning, to quantify the magnitude of springback. The twisting parameter, defined as the ratio of the total angle variation between two extreme sections over the distance between the two same sections, is strongly dependent on the material, with a small value of 8 degrees m(-1) for CuBe2, an intermediate value of 28 degrees m(-1) for pure Cu and a high value of 45 degrees m(-1) for CuFe2P. The relationship between 2D springback and twisting is highlighted.