Problem to be solved: to provide a burring processing method capable of forming a high flange height at the time of burring by forming a bottom hole at the bottom of a bottomed cylindrical shape.The berring processing method according to the present invention isThe bottom cylindrical shaped forming process S1 forming the bottomed cylindrical shapePressing the bottom surface 11 of the bottom cylindrical shapeThe pressing step S3 having a curved shape in which the center of the bottom surface 11 is convex toward the inside isA bottom hole forming step S5 forming a circular underhole on the bottom surfaceThe bar ring processing step S7 which burns the burring punch 29 into the cylindrical shape in which the lower hole is formed and burnsEquipped withUnderhole forming processOn the inner peripheral side of the cylindrical shape, a punch die 19 is disposed on the outer circumference side without placing the plate presserIt is characterized in that the outer peripheral edge portion of the bottom surface 11 is pressed against the punching die 19 by punching punch 23 disposed inside the cylindrical shape to punch the hole.Diagram
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