Method for hydroforming and hydroformed product
The object is to raise the yield by greatly eliminating the disposed amounts of the tube ends, prevent wrinkles due to closing the mold while applying internal pressure, cutting the plurality of steps of hydroforming and pre-processing of the tube ends, cutting the mold costs by simplifying the mold mechanism, and obtaining a hydroformed product formed with a flange along its entire length. For this reason, the present invention provides a hydroforming method which places a metal tube to a lower mold in the state with the tube ends sticking out from it and injects a pressurizing fluid into the metal tube through the inside of a seal punch and gradually presses seal punches against tube ends of the metal tube to apply a predetermined pressing force and fill the inside of the metal tube with the pressurizing fluid to apply a predetermined internal pressure, next, in the state with the internal pressure and pressing force applied, lowers the upper mold and closes the mold so as to deform the tube and end the processing in the state with the tube ends sticking out from the mold, and, further, boosting the internal pressure in the metal tube after closing the mold and ending the forming operation and a hydroformed product processed using these methods and having a flange across the entire length in the longitudinal direction.
1. A hydroforming method comprising:
placing a metal tube having tube ends in a lower mold of a mold comprising the lower mold and an upper mold in a manner such that the tube ends stick out from the lower mold,
injecting pressurized fluid into the metal tube through an inside of a seal punch while pressing seal punches against the tube ends to apply a predetermined pressing force,
filling the inside of said metal tube with a pressurized fluid to apply a predetermined internal pressure, then, while applying said internal pressure and pressing force, lowering the upper mold to close the mold, deforming the tube along with the tube ends and finishing a forming operation with said tube ends sticking out from the mold, wherein said method is characterized in that when a sectional area of a metal part of said metal tube in a cross-section vertical to an axial direction of said metal tube is S 1 [mm 2 ], a sectional area of an inside of said metal tube is S 2 [mm 2 ], a yield stress of said metal tube is YS [MPa], and said predetermined internal pressure is P 1 [MPa], a force F 1 [N] pressed by said seal punches when closing the mold satisfies formula (1):
P 1 ·S 2 +0.3 YS·S 1 ≦F 1 ≦P 1 ·S 2 +0.7 YS·S 1 (1).
2. The hydroforming method as set forth in claim 1 , characterized by, after closing the mold, further boosting the internal pressure in said metal tube and ending the forming operation.
3. The hydroforming method as set forth in claim 2 , characterized in that when a sectional area of a metal part of said metal tube in a cross-section vertical to an axial direction of said metal tube is S 1 [mm 2 ], a sectional area of a cavity of said mold is S 3 [mm 2 ], a yield stress of said metal tube is YS [MPa], and an internal pressure boosted to after closing the mold is P [MPa], a force F [N] pressed by said seal punches when boosting the internal pressure after closing the mold satisfies formula (2):
P ·( S 3 −S 1 )+0.5 YS·S 1 ≦F≦P· ( S 3 −S 1 )+1.5 YS·S 1 (2).
4. The hydroforming method as set forth in claim 2 , 1 or 3 , characterized in that when a length by which the tube ends of said metal tube stick out from said mold before said seal punches press against the tube ends is made the seal length, said seal length is 2 to 4 times a plate thickness of said metal tube.
5. The hydroforming method as set forth in claim 2 , 1 or 3 , characterized in that a Rockwell hardness of a surface of said seal punches contacting said tube ends is HRC50 or more and a surface roughness is Ra 2.0 or less.