Friction Stir Incremental Forming of Preformed Sheets with Improving Bending Stiffness

To improve forming accuracy in friction stir incremental forming of sheet metal, embossed sheets were used for specimen. A5052-H34 aluminum alloy sheets were formed by a hemispherical tool made of high speed steel with a diameter of 6 mm. A pitch and height of embossed dots were set to 10 mm and 5 mm, respectively. The embossed sheets were formed into a frustum of conical shape with a height of 20 mm and a wall angle of 20° by friction stir incremental forming. When an embossed sheet was formed, the droop at the flange was reduced and formed height became closer to the ideal one. When the embossed direction was set to downward and the sheet was formed, the embossed dots were disappeared after forming.