| 摘要 |
PURPOSE:To perform a burring work of high working degree by bulging an annular heating area at a distance from a primary hole by a burring punch before burring a heating area in the vicinity of a hole edge part by said punch. CONSTITUTION:A heating jig 15 formed by providing a cooling ring 12 to a heating coil 4A consisting of concentrically installed inside coil 4a and outside coil 4b, is disposed in the vicinity of the peripheral edge part of a primary hole 1a of pipe material 1. Next, an annular area 9b at a distance from the hole 1a, is heated by high frequency induction heating by means of the outside coil 4b while restricting the heating area by cooling water; and a burring punch 3 is raised by a working force 5A through a rod 10, to bulge the heating area in hot state. In the same manner, an area 9a in the vicinity of hole 1a is heated by the inside coil 4a to hot burr the area 9a by drawing out the punch 3 with the aid of a working force 5B. In this way, a hot burring of large burring height can be performed.
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