ROLL FORMING DEVICE OF BELLOWS

PURPOSE:To improve the accuracy of a shape, etc., by setting the maximum outside diameter of an inner die and the minimum inside diameter of an outer die so that the press-contact part becomes linear and also a product can be drawn out by noncontact. CONSTITUTION:The maximum outside diameter of an inner die 11 functioning as a forming roll is set to 90-97% of the minimum inside diameter a1 of a product 10a so that a gap 12 becomes 3-10% of the minimum inside diameter a1 of the product 10a. The minimum inside diameter of an outer die 13 is set to 103- 110% with respect to the maximum outside diameter a2 of the product 10a so that a gap 14 becomes 3-10% of the maximum outside diameter a2. As a result, as for a press-contact part 15, an angle alpha from the center of the inner mold 11 becomes a linear contact state of 20-30 deg., and a material lead-in of a cylindrical base material 10 is executed gradually in a wide range. Accordingly, a selection of a material and setting of forming conditions are relaxed, the forming accuracy is improved, and also high reliability is obtained.