| 摘要 |
PROBLEM TO BE SOLVED: To provide upset parts which are suitable for mass production and inexpensive. SOLUTION: A stock 10 of a desired length is headed to form parts of a desired shape, a forming hole 13 with the inside diameter being identical over the whole length is formed in one end of the parts, and the parts are plastically deformed to form a tapered hole 14 in the headed part in which the diameter on the end face side is smaller than the inside diameter of the parts. The tapered hole in which the inner part is wider and the end face side is narrower does not need be formed by cutting, and a series of working steps are reduced to only the heading step, and the working steps are simplified. When these parts are mass-produced, the parts are formed only by the heading, the set-up time required therefor is reduced, and the manufacturing cost of the parts is also reduced. In addition, the parts are formed only by the heading, and hence no cutting chips are produced, and the material is not wasted.
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