| 摘要 |
PURPOSE:To form a branch pipe whose branching pipe part has the thickness uniform along its peripheral direction, by boring a primary hole at the prescribed position of a main pipe, where a branching pipe that is formed, and heating the peripheral part of this primary hole by a high frequency induction heating with the aid of an elliptically formed heating coil. CONSTITUTION:Both ends of a main pipe 1 having a primary hole bored at a prescribed position are fixed by clamps 3, and an elliptically annular heating coil 5A is set at the outer periphery of the boring part of primary hole so that the major axis a'-c' of coil 5A is directed to the axial direction of the pipe 1. Next, a burring punch 4 is inserted to the inside of pipe 1 and is set by fixing the front tip of a rod 6 to it. Then a high frequency oscillator is turned on to flow a high frequency current through the coil 5A thereby heating a burring- forming part by a high frequency induction heating. A working load is loaded on the rod 6 which maintaining a working temperature, to form a branching pipe part 2A by burring.
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