| 摘要 |
<p>[Problem] The purpose of the present invention is to provide a form-rolling die and form-rolling method for a compound screw that use a cylindrical material to be threaded, enable the high-precision mass production of compound screws having a right-hand thread portion and a left-hand thread portion on the same region, do not cause rolling defects such as slips, and in which blockages do not occur even in the unlikely event of shavings being generated. [Solution] A form-rolling die structure is provided with die members which are pressed against a material to be threaded and which have rigid surfaces that are relatively displaced. The die members are equipped with a plurality of independent concave portions which form a substantially parallelogram shape when viewed from the normal of a virtual surface obtained by connecting the outermost portions of each of the rigid surfaces, and which are recessed from the virtual surface. Two of the corners at the sites corresponding to the four corners of the substantially parallelogram-shape of the concave portions are rounded. The periphery of each concave portion in the cross-section along the direction of the normal is rounded along the periphery of the substantially parallelogram shape. The concave portions form a substantially truncated-pyramid shape. The sites equivalent to the ridge lines of the concave portions are rounded in cross-sectional view perpendicular to the ridge line, and bases (35) are provided in the deepest sites (34).</p> |
