| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a screw shaft with superior yield, and to provide a screw shaft for electric power steering. <P>SOLUTION: Form rolling is performed in a range that is longer than the sum of the required screw lengths of two products 2, 2 only to an axial center part of a columnar material 1 having a length substantially equal to the sum of the axial lengths of the two products 2, 2, and the columnar material applied with the form rolling is split at a position corresponding to the axial length of each of the two products. By one splitting step, the two products 2 each having a complete screw part 7' at an axial end thereof are formed, so that processing costs can be suppressed, and the yield can be improved. Further, by setting the range of a form rolling part 3 to be twice as long as a form rolling dice and substantially equal in length to the required screw length for the two products, the required screw length for the two products can be obtained at the complete screw part 7 excluding incomplete screw parts 6 formed at portions where the form rolling dice at both ends of the form rolling part does not pass. <P>COPYRIGHT: (C)2012,JPO&INPIT |
