| 摘要 |
PURPOSE:To prevent the formation of a thin thickness part by forming a rack tooth with flowing a metal material in the space between a hollow rod and auxiliary member, by performing a forging by inserting the auxiliary member with nearly flat both faces into the inner part of the hollow rod. CONSTITUTION:The auxiliary member 32 forming vertically flat faces 32a, 32b is inserted into the hole 30 of the hollow blank stock 34 having the hole 30 at the shaft core part. The external shape of the part excepting the flat faces 32a, 32b of the auxiliary member 32 is about equal to the inner diameter of the hole 30 of the blank stock 34, the both 32, 34 are integrated by a brazing, press-fitting, shrinkage fitting, etc., and gaps C1, C2 are formed vertically between both thereof. A forging is them performed in warm, hot, etc., by the lower die 38 having a tooth profile part 36 and the upper die 42 having the recessed part 40 in the shape about conforming to the outer peripheral face of the blank stock 34. In this case, the plastic flow becomes better and no thin thickness part is caused on the hollow rod because of the gaps C1, C2 existing between the hollow rod 34 and auxiliary member 32. No center part of a rack tooth 16 is made thinner than both end sides as well.
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