| 摘要 |
PURPOSE:To execute punching with high yield by reducing the quantity of punch chips, by placing a rough forging of a metallic base material on a hole base whose hole diameter is variable, punching a hole by a punch whose diameter is smaller than a desired diameter, and after that, forming a prescribed hole diameter, expanding the hole by a conical punch. CONSTITUTION:A rough forging 5 being a metallic base material is placed on a hole base 1 which makes a diameter of a hole 11 variable, and a hole is punched by a punch whose diameter is smaller than that of the hole to be drilled. Subsequently, the hole punched in the rough forging 5 is expanded by use of a conical punch 3. In this case, the bottom part of the cone, namely, the maximum diameter of the punch 3 is made to conform with the diameter of a hole to be punched finally, and as the punch 3 advances, the diameter of the hole 11 of the hole base 1 is expanded gradually. In this way, the prescribed hole diametr as shown in the figure is obtained. |
