To provide a hydroforming method by which a bulged part, which is high in the formed height and excellent in flatness, is stably obtained when manufacturing a product having the bulged part on the midway of a tubular body by hydroforming.
During the process of performing hydroforming by using a die in which a lower die 1 having a bulging hole 3 is combined with an upper die 2 and a counter punch 4, to which energizing force is applied, is arranged in the bulging hole 3 by using a punch, the surface roughness of which is equal to or smaller than the surface roughness of the inner wall face of the bulging hole including a round part as the counter punch 4, a material is freely made to flow along the inner wall surface of the bulging hole 3 of the die and the surface of the counter punch 4, when bringing the material into flow deformation by adding internal pressure and shaft pushing force 6. By making the material flow on the surface of the counter punch free, the desired forming height and the flatness are easily obtained without being biased to one part nor concentrating strain on one part of the bulged part 7.
OTSUKA MASAHITO
MORIKAWA SHIGERU
Okada Manri
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