Press forming method and plate material expansion device used in said method

A press forming method comprising:

• an expansion step of a preceding process;
• and
• a forming step of a following process;
• wherein:
• the expansion step is a step in which at least partial expanding of an end portion of a plate material is performed so as to obtain a blank material having the end portion and a dimension suitable for the forming step, and to feed the blank material into the forming step;
• the forming step is a step in which the blank material fed from the expansion step is formed by constraining a predetermined part of the end portion thereof;
• the expansion step includes:
• a stretching step of pressurizing and stretching the end portion of the plate material with a stretching processing tool;
• and a smoothing step of flattening the end portion of the plate material which is deformed into a nonplanar shape in the stretching step;
• a bending step of bending a tip end portion of the plate material before the stretching step is performed, and
• the stretching step is performed while a curved portion of the tip end portion of the plate material bent in the bending step is hooked on a holding processing tool.

A press forming method comprising:

• an expansion step of a preceding process;
• and
• a forming step of a following process;
• wherein:
• the expansion step is a step in which at least partial expanding of an end portion of a plate material is performed so as to obtain a blank material having the end portion and a dimension suitable for the forming step, and to feed the blank material into the forming step;
• and
• the forming step is a step in which the blank material fed from the expansion step is formed by constraining a predetermined part of the end portion thereof;
• the expansion step includes:
• a stretching step of pressurizing and stretching the end portion of the plate material with a stretching processing tool;
• and a smoothing step of flattening the end portion of the plate material which is deformed into a nonplanar shape in the stretching step;
• the stretching step is a step that is gradually performed by performing a plurality of stretching processings in which a width of the end portion of the plate material to be stretched each time is different;
• and
• the stretching step is a step that is performed in a state where the end portion of the plate material is constrained by a bead part of a member having the bead part formed thereon.

The A press forming method comprising:

• an expansion step of a preceding process;
• and
• a forming step of a following process;
• wherein:
• the expansion step is a step in which at least partial expanding of an end portion of a plate material is performed so as to obtain a blank material having the end portion and a dimension suitable for the forming step, and to feed the blank material into the forming step;
• and
• the forming step is a step in which the blank material fed from the expansion step is formed by constraining a predetermined part of the end portion thereof;
• the expansion step includes:
• a stretching step of pressurizing and stretching the end portion of the plate material with a stretching processing tool;
• and a smoothing step of flattening the end portion of the plate material which is deformed into a nonplanar shape in the stretching step;
• the stretching step is a step that is gradually performed by performing a plurality of stretching processings in which a width of the end portion of the plate material to be stretched each time is different;
• a bending step of bending a tip end portion of the plate material before the stretching step is performed, and
• the stretching step is performed while a curved portion of the tip end portion of the plate material bent in the bending step is hooked on a holding processing tool.