| 摘要 |
PROBLEM TO BE SOLVED: To reduce the number of times in the machining operations with mandrels, in manufacturing a rack-formed tubular member used for an automobile steering device or the like, in such a manner that a steel tube as the base material is pressurized in a part of the length to make the outer circumferential surface a flat plane partly, that, with a rack forming die held in contact with the flattened planar part, one or more mandrels are pushed into the steel tube, and that the inner surface of the flattened planar part is successively drawn through a plurality of drawing places. SOLUTION: The mandrel is such that both side faces in the drawing places are vertical to the face opposed to the inner face of the flattened planar part of the steel tube and that an interval between both side faces in the drawing places is the same for all mandrels to be used in the drawing places.
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