To reduce the number of work processes and improve dimensional accuracy and free change in thickness.
This method is a manufacturing method of a hollow member for manufacturing the hollow member the cross-sectional shape of which is different in the longitudinal direction. By extruding a material to be formed from a die hole 10A where the tip part of a mandrel 6 is situated, the hollow member the shape of the outer peripheral surface of which is corresponded to the shape of the inner peripheral surface of the die hole 10A and the shape of the inner peripheral surface of which is corresponded to the shape of the outer peripheral surface of the mandrel 6 is extruded. At the time of extruding that hollow member, at least either one of the cross-sectional shape of the die hole 10A or the cross-sectional shape of the tip part of the mandrel 6 which is situated in this die hole 10A is changed and, after that, after the hollow base stock after extruding, puts into a mold, by pressurizing the inside of the hollow base stock, bulge forming is executed.
KATO MASATSUGU
SUZUKI TAKAHIRO
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