
A plurality of first projections 113a are provided in a first side wall portion 111a of a grooved section 111 formed by bending part of a sheet-like workpiece to have a U-shaped cross-section, which projections extend away from a connecting portion (top) 111c. Since the first side wall portion 111a deforms to widen a groove width of the grooved section 111 due to spring-back, a tip end of the first projection 113a is first brought into contact with the inner wall 110a. Therefore, a reaction forc...











