METHOD OF MAKING CHAMFERED OPENINGS Russian patent published in 1997 - IPC

FIELD: plastic material working. SUBSTANCE: method comprises steps of pressing out cylindrical recess in blank, trimming said recess, pressing out chamfer with formation of rod of pressed out material. Diameter of said cylindrical recess is less than diameter of rod and diameter of said rod is less than diameter of opening to be made. At pressing out chamfer bottom portion of recess is free for material yielding. Then opening is punched and scrap is removed. In order to make second chamfer on lower part surfaces of blank at punching openings, tools in the form of punch and die mounted with increased gap are used. EFFECT: enhanced efficiency. 4 cl, 3 dwg