Patent ID: 7631425

Claim:
A method for manufacturing a rocker arm, comprising the steps of: obtaining a bent workpiece with prepared apertures, wherein the bent work piece includes a pair of side walls disposed in parallel with each other, and connecting walls for connecting the side walls, the pair of side walls each having a prepared aperture formed by driving an aperture forming punch into each side wall; and forming a roller supporting shaft fixing aperture by inserting sizing punches respectively into each prepared aperture, wherein each sizing punch has a tapered push enlarging portion at a tip end portion, a basal end side of the push enlarging portion being larger than each prepared aperture in diameter, and a tip end side of the push enlarging portion being smaller than each prepared aperture in diameter, whereby the push enlarging portion causes plastic flow of an inner peripheral portion of each prepared aperture in a sheared region of each prepared aperture so that the plastically flowed portion moves to an inner peripheral surface of each prepared aperture in a fractured region of each prepared aperture to finish the inner peripheral surface of each prepared aperture to thereby obtain roller supporting shaft fixing apertures, whereby the tapered push enlarging portion of each sizing punch respectively passes completely through each prepared aperture to form a finished smooth surface on the inner peripheral surface of each prepared aperture.