Abstract: A method prevents a cylindrical body from buckling in externally curling edges of both side portions by pressing curling dies in an axial direction after molding the cylindrical body having a drop portion whose outer diameter is small and two side portions whose outer diameter is large by enlarging a cylindrical material made of aluminum alloy by electromagnetic molding. In curling the edges of the side portions, a buckling preventing die restrains an outer periphery of the drop portion of the cylindrical body. Because the buckling preventing die receives the axial compression force of the curling dies, it can prevent the cylindrical body from buckling and deforming. The buckling preventing die is what a split die disposed on the side of an outer periphery of the cylindrical material in the electromagnetic molding is used as.

Abstract: There is provided a method for preventing a cylindrical body from buckling in externally curling edges of both side portions by pressing by curling dies in an axial direction after molding the cylindrical body having a drop portion whose outer diameter is small and the both side portions whose outer diameter is large by enlarging a cylindrical material made of aluminum alloy by electromagnetic molding. In curling the edges of the both side portions, a buckling preventing die restrains an outer periphery of the drop portion of the cylindrical body. Because the buckling preventing die receives the axial compression force of the curling dies, it can prevent the cylindrical body from buckling and deforming. The buckling preventing die is what a split die disposed on the side of an outer periphery of the cylindrical material in the electromagnetic molding is used as it is.

Abstract: Disclosed is a method of making a rim having hollow flanges formed on its opposite annular edges. It comprises the steps of: cutting an elongated metal band of a fixed width to provide metal strips of a predetermined length; rolling a selected metal strip into a ring; welding the opposite ends of the ring; curling each annular edge of the ring outward; and roll-forming the main annular part to define a well along the center line of the main annular part. The method further comprises the steps of: bending the opposite bead areas toward the center well; closing the gap between each curl edge and the counter bead area; and unbending the opposite bead areas into the final rim shape.