| 摘要 |
PURPOSE:To make a base material flow to a space part, as well, by pushing pressure of a punch, and to prevent the generation of a piping defect by providing the space part between the upper and lower mandrels of the inside periphery of a large diameter part in a punch descending end, of a stepped forging metallic die for bulging the large diameter part to the outside of a cylindrical base material. CONSTITUTION:When a cylindrical base material 10 is fitted and inserted into a hole 6 of a die 3, a large diameter part 10a of the base material 10 is positioned in an annular recessed part of the die 3, and a gap 5 is left and positioned in the outside peripheral side. Subsequently, when upsetting by a punch 5 is executed, an outer punch 5a of the punch 5 makes pushing pressure work on the large diameter part 10a of the base material 10, a material of the large diameter part 10a fills a gap S in the direction as indicated with an arrow A, and also, flows into a space part 18 between upper and lower mandrels 8, 9 in the direction as indicated with an arrow B. Also, a projecting part 24 is formed on the inside peripheral surface of the large diameter part, without generating a piping defect. Subsequently, the projecting part 24 is cut and removed, and a desired cylindrical stepped forgings is obtained.
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