| 摘要 |
PROBLEM TO BE SOLVED: To provide a flat die for the form rolling of a worm shaft in which a flat part of a predetermined width for a straightening die needs not be provided on a work adjacent to a circumferential surface form rolling part of a columnar material, and applicable works are not limited, while the bend of the work by the form rolling is small, and a step for straightening is unnecessary. SOLUTION: The lead angle of a thread at a starting end of biting parts 30 of flat dies 6, 7 is set to beβ1; the lead angle of a thread at a terminating end of finishing parts 31 of the flat dies is set to beβ2, and the relationship ofβ1 <β2 is set. Threads are formed by continuously and smoothly changing the lead angle from the lead angleβ1 of the thread at the starting end of the biting parts of the flat dies to the lead angleβ2 of the thread at the terminating end of the finishing parts of the flash dies. COPYRIGHT: (C)2008,JPO&INPIT
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