| 摘要 |
PROBLEM TO BE SOLVED: To prevent buckling or corner wrinkles at a swollen part when the ratio of radius of a corner part of the swollen part and the pipe diameter is small and even a processing condition is severe by varying the increased volume of liquid pressure against the increased volume of the shaft pressing stroke to be low in an early stage of the shaft pressing, high in a middle stage, and low again in a final stage, so that it reaches the final pressure. SOLUTION: At an early stage for pressing a shaft from the processing start till a given point, increased volume of fluid pressure is reduced against increased volume of a stroke of shaft pressing. In a stroke of a shaft pressing early stage where the swollen height of a metallic pipe is within a range of 1/4-3/4 of the swollen part diameter, a liquid pressure P1 is 50-90% of a given fluid pressure. At a middle stage of shaft pressing where the swollen height of the metallic pipe is within a range of 1/2-3/2 of the swollen part 5 diameter, a liquid pressure P2 is 150% or more of the liquid pressure. At the final stage of shaft pressing, a final pressure P3 is used while the liquid pressure is lowered, so that a corner part of the swollen part is enfolded along a corner part of a mold 2.
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