| 摘要 |
PROBLEM TO BE SOLVED: To realize remarkable weight reduction in a technique, which forms a rack bar for a steering mechanism of a vehicle from a stock tube by plastic working, compared with conventional working techniques. SOLUTION: Before conducting a form rolling step of making rack teeth with metal dies, the wall thickness of a portion that becomes the axial part of a rack bar is decreased as follows: when the original wall thickness of the stock tube is t<SB>0</SB>, the diameter of a portion 10-1 that becomes a tooth profile of a rack bar is reduced, and the wall thickness of the portion 10-1 is maintained or slightly increased to an increased wall thickness t<SB>1</SB>; and the wall thickness of a portion 10-2 that becomes the shaft part of the rack bar is decreased to a decreased wall thickness t<SB>2</SB>, for example to one half of that of the stock tube. By the decrease in the wall thickness, the length of a blank is extended to L<SB>1</SB>from L<SB>0</SB>, which is the original length of the stock tube. Thereafter, tooth-profile forging is conducted using metal dies, so that a tooth profile 11 is formed. COPYRIGHT: (C)2008,JPO&INPIT
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