Patent ID: 8051696

Claim:
A method of press forming an aluminum alloy sheet into a formed product panel having an arcuate ridge line and at least two curved faces surrounding the ridge, using a press device comprising a die, a blank holder at an outer periphery of the die, a first punch having an arcuate ridge line part for shaping the arcuate ridge line of the panel, and a substantially annular second punch surrounding the first punch, wherein the second punch is movable relative to the first punch in the direction toward and away from the die independently of the movement of the first punch toward and away from the die, and wherein the arcuate ridge line is curved in the direction toward and away from the die, the method comprising the steps of: positioning an aluminum alloy sheet between the die, on one side of the aluminum alloy sheet, and the first and second punches on another side of the aluminum alloy sheet; holding an outer peripheral part of an aluminum alloy sheet between the die and the blank holder; positioning the second punch at a position advanced toward the die relative to the first punch; causing at least one of the die and the first punch to be relatively moved toward one another toward a dead bottom point, beginning at a time when the second punch is at the position advanced toward the die relative to the first punch, whereby the aluminum alloy sheet is engaged between the die and the advanced second punch before the arcuate ridge line is formed between the die and the first punch; and thereafter continuing to move at least one of the die and the first punch toward one another to the dead bottom point, to form the formed product panel having the arcuate ridge line, wherein at the dead bottom point, the second punch is shifted away from the position advanced toward the die relative to the first punch.