| 摘要 |
According to the present invention, in the first process, a pipe end of a long pipe is bent with a radius of curvature which is larger than a minimum radius of curvature to form a large R portion. That is to say, bending with a large radius of curvature (R) is performed to form a large R portion in a region in which cracking or excessive reduction of plate thickness of the bend outer-side portion, or buckling of the bend inner-side portion does not occur. Subsequently, in the second process, the pipe is bent with a small radius of curvature form a small R portion by pressing a pipe-end portion of the pipe from a pipe-end direction while fixedly holding the bend side wall of the pipe. In this way, it is possible to obtain an R-minimum elbow configuration irrespective of magnitude of an amount of elongation of material and further without special equipment or mechanisms, by minor modification of present equipment. |
