| 摘要 |
PURPOSE:To prevent the flaw generation of a product by bending a metal sheet so that the end part at opening edge side of a metal sheet approaches each other by providing the bend means of a roller, etc. CONSTITUTION:A recessed part 320 is provided on the outer die 32 and both side faces in opposition of the upper stream zone 321 are formed in V-shaped cross section as well. The main body part 332 engaging with the inner die 33 via the outer die downstream zone 322 together with a flat plate like fitting part 331 and the prescribed gap is provided on the inner die 33. The surface treated metal sheet is bent in circular arcuate shape along the center axis via the roll arranged at the upper stream of a forming machine 3 and led to the forming machine 3. In this case, the metal sheet is guided to the upperstream zone 321 of the outer die recessed part 320 and bent in the U shape inclined so as to approach each end part of the opening edge each other. The U-shaped sheet by this method is formed surely in each end part at the round pipe forming time, so the generation of the breakdown can be prevented.
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