PURPOSE: To enable the undeformed band length after forming to be formed effectively short with less forming force by so forming the material to be formed that the material to be formed and a lower die do not contact except the end part of the material to be formed and the contact part of the lower mold from the start of forming until completion.
CONSTITUTION: In the foregoing one point contact forming, the dies of the construction in which not only the material to be formed 8 makes contact with a lower die 6 with its end part 9 at all times during forming but also the end part 9 may be closely contacted to an upper die 5 even at the extreme limit of C-forming (undeformed band 14 length lF=O) is required. To this end, the offset amount F of the curvature centers OU, OL of the upper and lower dies are so selected that the angles ψ, θ of the case when it is assumed that the material 8 made close contact with the die 5 become ψ-θ>0. At the same time there is a need for arranging the dies in such a manner that the material 8 and die 6 do not contact at the parts other than the end part 9 and contact point 10 from the start of forming until completion. Because of this, the upper and lower die curvature radii RU, RL, offset amount F, die 6 length, etc. are correctly selected. Here, RL≥RU is easier to execute but RL< RU is equally well.