| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for fabrication of a shaft having a bulge part wherein the compressive force needed for making bulge in the middle of a metal shaft with larger diameter than that of the shaft is reduced as much as possible. SOLUTION: A work, which is held by a pair of rotating holders at a suitable interval D0 (initial grip interval), is rotated around the shaft and bent by stronger stress than the proof stress. The work between the rotating holders are repeatedly bent and bent back so as to reduce the yield stress of the work. Thereafter, the work is rotated, bent and pressed by the compression by drawing the both of the rotating holders nearer to each other, so that protrusions formed inside of the bending part of the work between the rotating holders may be built up all round the work to form a required enlarged part. Thereafter, the work is straightened by making the shaft axis of the rotating holders straight, and by stopping the compression and rotation, the required bulge part is formed at any location of the middle of the work.
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