Residual stresses and springback reduction in U-channel drawing of Al5182-O by using a servo press and a servo hydraulic cushion

The increasing use of aluminum alloys in automotive industry brings new challenges regarding formability and springback. Servo presses and servo hydraulic cushions can accurately control ram motion and blank holder force during the forming process, reducing the difficulties encountered in forming Al alloys. This study presents an experimental and numerical analysis of springback and residual stresses induced during the U-channel drawing of Al 5182-O. During the U-channel drawing, the draw-in of the sheet material into the die cavity is controlled by blank holder force. So, the material is under stretch bending condition when it slides around the die corner radius. When the material passes the die corner radius it unbends. The reverse loading resulted from the unbending process provides heterogeneous stress distribution through the sheet thickness in the wall section. The effect of post stretching, applied by the use of a servo hydraulic cushion, on reduction of residual stresses and springback at the wall is investigated. The benefit of using servo hydraulic cushion for reducing springback and residual stresses has been demonstrated experimentally. Results illustrate a significant reduction of residual stresses and springback when post stretching is applied.