METHOD FOR MANUFACTURING WASHER CAP FOR PEM NUT

The present invention is based on a multi-stage forging method by multiple punches (20) and a dies (25). A method for manufacturing a washer cap in which one end is protruding by a circular groove (13) in the axial direction, and the other end consists of a head part (11), which is expanded toward the radial direction of the circular groove, comprises: (a) a primary processing step for manufacturing a primary molded product (31) by curve-molding an edge part of a cut material; (b) a secondary processing step for manufacturing a secondary molded product (32), in which the head part is primary-molded, by expanding the other edge part toward the radial direction while a curve-molded part of the primary molded product is molded preliminarily; (c) a tertiary processing step for manufacturing a tertiary molded product (33) by forming a combining groove (14) on a circumference of the head part preliminarily while a concave groove (12) in the axial direction is formed preliminarily to the center of the other end of the secondary molded product; (d) a forth processing step for manufacturing a forth molded product (34) by molding the concave groove of the tertiary molded product as a circular groove; and (e) a fifth processing step for manufacturing a fifth molded product (35) of a final size standard by a overall finishing process of the forth molded product. Accordingly, the method for manufacturing a washer cap, which is assembled in a pem nut, is capable of securing a superiority of mechanical properties, which are properties of a cold forging, by introducing a precision multi-stage forging while promoting a productivity enhance, an equalization of a product quality, costs reduction etc.