| 摘要 |
<p>A punch 1 includes a forming land portion 2 formed in parallel with a punch axis 7, a forming R-portion 3 having an arc-shaped cross-section and formed continuously with the forming land portion 2 on a tip end side with respect to the forming land portion 2, and a recess portion 5 formed on a base end side with respect to the forming land portion 2 and having a diameter smaller than a diameter of the forming land portion 2. A Rockwell hardness HRF of the blank 20 is within a range of 65 to 105. The curvature radius R of the forming R-portion 3 of the punch 1 is set to be larger than the thickness L of a cylindrical peripheral wall portion 21 of the forged product 25. The length B of the forming land portion 2 of the punch 1 is set within a range of 0.05 to 0.15 mm. The recess width C of the recess portion 5 with respect to the forming land portion 2 of the punch 1 is set within a range of 0.15 to 1.0 mm.</p> |
