Bending method

A bending method that feeds a workpiece material made of metal between rollers and bends the workpiece material while rolling the workpiece material with the rollers,

• the workpiece material having an elongated shape, and a first thickness portion and a second thickness portion connected to each other and forming a setting angle of 90 degrees, the bending method comprising the steps of:
• before bending, making a shape of the workpiece material a straight line or a bend with a bend radius dimension larger than a target bend radius dimension;
• before bending, setting a thickness dimension of a cross section of the first thickness portion along a bend radius direction so as to increase from an inner side toward an outer side in the bend radius direction, and setting a thickness dimension on an outer peripheral side of the first thickness portion to be a dimension M and a thickness dimension on an inner peripheral side of the first thickness portion to be a dimension m, the dimension m being also a target thickness dimension in a cross section along the bend radius direction of the first thickness portion after bending;
• before bending, setting a thickness dimension of a cross section of the second thickness portion to be a constant dimension N;
• wherein M equals to m(R/r), and N equals to n(R/r) where n is a target thickness dimension of a cross section of the second thickness portion after bending, R is an outer radius dimension of the first thickness portion after bending, and r is an inner radius dimension of the first thickness portion after bending, and
• feeding the workpiece material, with the dimensions set before bending, between the rollers and bending the workpiece material while rolling the workpiece material with the rollers.