| CPC B21D 53/88 (2013.01) [B21D 22/26 (2013.01); B21D 24/04 (2013.01); B21D 37/10 (2013.01)] | 16 Claims |
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1. A press forming method for an outer panel of an automobile, for press forming a metal sheet into the outer panel of the automobile, the outer panel having a character-line and a panel surface portion that is continuous on both sides of the character-line, the press forming method comprising:
providing a punch, a die facing the punch, and a blank holder facing end portions of the die, wherein
the punch includes:
a ridgeline to form the character-line;
a punch side forming surface portion to form the panel surface portion; and
a punch side elastic body supported to protrude toward the die than the punch side forming surface portion so that the punch side elastic body is able to come into contact with the metal sheet, along a character-line equivalent portion corresponding to the character-line in the metal sheet, at a position away from the character-line equivalent portion, on a side larger in tension in the press forming among portions on both sides sandwiching the character-line equivalent portion, and
the die includes:
a valley-line to form the character-line in cooperation with the ridgeline;
a die side forming surface portion to form the panel surface portion; and
a die-side elastic body supported to protrude toward the punch than the die side forming surface portion so that the die side elastic body comes into contact with and press the metal sheet, along the character-line equivalent portion, at a position away from the character-line equivalent portion, on a side smaller in tension in the press forming among portions on both sides sandwiching the character-line equivalent portion,
setting an amount of protrusion of the punch side elastic body from the punch side forming surface portion so that the punch side elastic body:
comes into contact with the metal sheet before the ridgeline of the punch contacts the metal sheet when the die is relatively moved toward the punch; and
becomes flush with the punch side forming surface portion at a bottom dead center;
setting an amount of protrusion of the die side elastic body from the die side forming surface portion so that:
the die side elastic body comes into contact with the metal sheet before the ridgeline of the punch contacts the metal sheet and the metal sheet is plastically deformed when the die is relatively moved toward the punch; and
a friction force between the die side elastic body and the metal sheet becomes equal to or larger than an absolute value of a difference between tensions acting on the portions on both sides sandwiching the character-line equivalent portion when the metal sheet is press formed, where the friction force is given by a product of:
a load of the die side elastic body pressing the metal sheet at the press forming the metal sheet; and
a friction coefficient between the die side elastic body and the metal sheet;
relatively moving the die toward the punch in a state where both end portions of the metal sheet are sandwiched between the die and the blank holder;
bringing each of the punch side elastic body and the die side elastic body into contact with the metal sheet; and
press forming the metal sheet into the outer panel of the automobile, the outer panel having the character-line formed by means of the ridgeline and the valley-line, by relatively moving the die toward the punch up to the bottom dead center with the punch side elastic body and the die side elastic body both being in contact with the metal sheet.
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