To provide a flat die for form rolling of a worm shaft in which the bend by the form rolling is small, and any step for straightening is unnecessary even when the diameter of a cylindrical part forming a straightening die adjacent to a circumferential surface form rolling part of a columnar material is different from the rolling circular diameter corresponding to the lead angle of the flat die.
A boundary line 24 at an end of a die tooth flank forming part of an upper face 71 of a flat die 7 on the side opposite to the moving direction 13 by the form rolling of a worm shaft is a continuously changing boundary line 24 matched with the moving locus formed by an end 2 of a circumferential surface form rolling part of a work 12 by the form rolling when using dies 9, 11 for straightening. A chamfering flank face 23 is formed on the upper face 71 of the flat die 7 outside the boundary line 24.
COPYRIGHT: (C)2008,JPO&INPIT
MURAI YASUHIRO
TAKIMOTO SHINYA
