| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing bolts by which timewise and financial load required to manufacture the bolts is reduced by making it possible to manufacture the bolts with necessary mechanical properties without applying any heat treatment. Ž<P>SOLUTION: In a shaft-like workpiece WK cut into a prescribed length, a head T of the bolt is preformed in the upper end part of the workpiece WK with a die 10 for manufacturing the bolts, also the diameter is reduced by contracting the under part of the head T and an under head part N is preformed. Next, in the workpiece WK, the outside diameter of the under head part N is further contracted with the die 20 for manufacturing the bolt and the head T is further preformed in the state where the expansion of the outside diameter of the under head part N is controlled. Furthermore, in the workpiece WK, the outside diameter of the under head part N is further contracted with the die 30 for manufacturing the bolts and the head T is finally formed in the state where the enlargement of the outside diameter is controlled. In this way, the forming of the head T is performed in the state where the Bauschinger effect is suppressed. A male thread part is reshaped in the preformed under head part N by form rolling or cutting. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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