To prevent the buckling caused on bending and to form in a well shape even in a different shaped cross-section bending tube by using a die of installing a projection part at an initial contact place to a tube as the raw material and locally enlarging the tensile strain of the contact place of the forming die in bending the bending tube.
An upper die 11 supported with an upper holder 14a and having a projection 11a is arranged freely moving up and down making a post 8 as a guide, it is matched to a lower die 12 at the lowest point and these are closed. A bending tube 1 is formed by pressing the axial direction load 13a of a pressing rod 13 into both ends of a raw material tube supported with an upper holder 14a and a lower holder 14b, machining in a taper like, loading a pressing post 9 with a pressing load 9a in the state of loading an inside pressure 10 in the raw material tube, and bending with pressing with the upper die 11 and the lower die 12. A dimple is generated at the place of the projection 11a made in contact with the bending tube 1, with this dimple, the axial direction tensile strain is made large even nearby the point of inflection, so buckling is prevented.
IWAKURA AKITA
YOSHITOMI YUJI
TANAKA SHINJI
SATO TOSHIMI
UCHINUMA YOSHIAKI
KUROKAWA TAKEO
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