| 摘要 |
PROBLEM TO BE SOLVED: To manufacture a metal tube having a characteristic equivalent to a general roll forming method by a die forming method by controlling the deterioration of a mechanical characteristic owing to shearing strain and bending strain. SOLUTION: In a forming die for manufacturing a welded metal tube by which a metal strip S is formed into an open tube shape, a forming through hole whose inside diameter becomes small from the inlet side toward the outlet side of the metal strip S is formed, and the cross sectional profile of the forming through hole from the inlet side to the smallest diameter part 11 is composed of an arc-like curved surface 12 having the center C on the surface orthogonal to the central axis of the die passing the smallest diameter part 11. The cross sectional profile of the part from the middle between the inlet side and the smallest diameter part 11 to the smallest diameter part 12 is also allowed to be formed into the arc-like curved surface 12. When the radius of curvature of the arc-like curved surface I2, the plate thickness of the metal strip S, Young' s modulus and a yield stress are respectively expressed by R, t, E andσe, the radius R of curvature is preferably set to t.E/50σe or above.
|
