To propose such technique in which the strength is improved while balanced as a whole in terms of an expanded member to be worked.
This invention relates to a tube hydroforming method where, in the cavity 2 of a die which is hermetically sealed, the member 3 to be worked is formed into a shape matching to the inner surface 2a of the cavity by expanding a tubular member 3 to be worked by imparting forming hydraulic pressure p to the inside of the member and closely contacting the member 3 to be worked with the inner surface 2a of the cavity. The member 3 to be worked which is preliminarily formed so that prescribed spaces 5a, 5b ... are formed in the prescribed positions between the outer surface 3a of the member 3 to be worked and the inner surface 2a of the cavity and the circumference of the cross section of the member 3 to be worked is longer than the circumference of the cross section of the cavity 2 is set in the cavity 2 and the forming liquid pressure is imparted to the inside of the member 3 to be worked.
ISOJIMA YOSHIHARU
KATO YOSHIHISA
HORI NAOKI
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