| 摘要 |
In the present invention, die parts having rigid surfaces that are relatively displaced with respect to a thread material (B) whilst crimping the same are used to form roll a double-threaded body (D). The die parts are provided with a double-threaded-part forming region (U) in which a plurality of recesses, which have an approximately parallelogram shape when viewed from the normal direction of a virtual surface obtained by connecting the outermost surfaces of the die parts and are recessed from the virtual surface, are provided in a plurality of rows along the relative displacement direction. The die parts further include a region in which the array pitch of the recesses within the double-threaded-part forming region (U) in the relative displacement direction decreases from a side that is upstream during relative displacement to the thread material to a side that is downstream during the same. Thus, when a double-threaded body is formed, rolling defects related to cylindrical thread materials are reduced, and the mass production of highly precise double-threaded bodies is possible. |
