| 摘要 |
PURPOSE:To form an annular overhang part for coupling without exposing a base metal on the inside surface, by providing a through-hole on a clad material, etc., covering the inside circumferential surface of the through-hole with a covering material by means of the primary burring working, and subsequently, performing the secondary burring working. CONSTITUTION:A through-hole 6 is punched to a flange 10, etc. formed by a clad material, etc., the primary burring working is performed by pressing in a punch 8 from a covering material 2 side, and an overhand part 12 is projected and formed on the side of a base metal 4. A through-hole 14 whose inside circumferential surface has been covered with a covering material 2 is formed by cutting and removing only projecting height (h) of this annular overhang part 12. Subsequently, the secondary burring working is performed by pressing in a large diameter punch 16, and an annular overhang part 20 projected to the side of the base metal 4 is formed on the clad material 10 received by a die 18. This annular overhang part 20 is formed in a state that an inside circumferential surface 24 and a tip surface 26 of a through-hole 22 formed on its inside surface have been covered with the covering material 2. |
