FORMING METHOD OF PRODUCT STEPPED ON OUTSIDE CIRCUMFERENCE BY COLD FORGING

PURPOSE:To enable the pressure forming using open dies of simple construction and to improve productivity and die life by forming a projecting cylindrical part in the upper part of a circular cylindrical blank material by backward extrusion, and forming a hollow base part bulging outward in the lower part thereof by extrusion. CONSTITUTION:A method of forming a product W stepped on the outside circumference consists of three stages including the 1st and the 2nd preliminary and finish forming stages using dies 11A-11C, punches 12A-12C and knockout pins 13A-13C. A recessed surface 14 is formed on the top surface of a circular columnar blank material S and a small projecting part 15 on the bottom surface by upsetting in the 1st stage in order to make the extrusion in the 2nd stage easy. A projecting cylindrical part 2 is formed in the upper part of the formed part S1 obtained in the previous stage by backward extrusion and the downward small diameter part 3a of a solid leg part 3 on the bottom surface by backward extrusion, in the 2nd stage. A hollow base part 1 of a hexagonal shape bulging outward is formed in the lower part in the part 2 of the formed part S2 obtained in the previous stage and a leg part 3 at the bottom end by extrusion, in the 3rd stage. The dies of a simple open type are used in the 2nd and the 3rd stages to form the product under pressure without restraint.