| 摘要 |
PURPOSE:To reduce a pipe in diameter while forming a sufficiently thick shoulder part without buckling by performing diameter reduction by rotary casting after increasing the thickness of a pipe end part axially toward an internal diameter side, and then performing axial upsetting work. CONSTITUTION:A tubular material 4 heated up to about 1,250-1,150 deg.C is held by a half die 51 and intruded into a punch 61 from a pipe end, and axial upsetting work is carried out by a half die 52 and a punch 62 to form a thick part 7 on an internal diameter side at a specific distance l' from the pipe end. The blank material 4 is cast by using a tap 11 while rotated to reduce the material from the pipe end to the thick part 7 within a specific range to a specific external diameter. Then, axial upsetting work is performed by a half die 54 and punch 63 and the material 4 of the diameter-reduced parallel part elongated by said rotary casting is moved axially and an underfill part 8 is supplemented to make the shoulder part of the diameter-increased part sufficiently thick; and the reduced part is increased in diameter slightly toward the internal-diameter part slightly.
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