Spinning method for forming pipe end

摘要

When the necked portion is formed at the end of the pipe material by the spinning method, working rollers are restricted so as to return immediately before the pipe end instead of being allowed to axially move beyond the end of the working object pipe. The diameter reduction amount of the pipe end is set smaller than that of the most diameter reduced portion connecting to the pipe end. A protruding portion of so-called bellmouth shape is formed at the working end, thereby preventing generation of fractures originated from the working end of the base portion or the welded portion and generation of wrinkles during the spinning.