Plate forging of tailored blanks having local thickening for deep drawing of square cups

A plate forging process of tailored blanks having local thickening for the deep drawing of square cups was developed to improve the drawability. A sheet having uniform thickness was bent into a hat shape of two inclined portions, and then was compressed with a flat die under restraint of both edges to thicken the two inclined portions. The bending and compression were repeated after a right-angled rotation of the sheet for thickening in the perpendicular direction. The thickness of the rectangular ring portion equivalent to the bottom corner of the square cup was increased, particularly the thickening at the four corners of the rectangular ring undergoing large decrease in wall thickness in the deep drawing of square cups became double. The degree of thickening can be adjusted by controlling the punch stroke in the bending. By using the tailor blanks having local thickening, not only the decrease in wall thickness at the bottom corner of the square cup was prevented, but also the limiting drawing height of the cup without fracture was increased to 28.3 mm, whereas that for the uniform blank was 21.3 mm.