Method for the manufacture of an ornamental head lug of the single unit type for use in bicycles

Method for the manufacture of an ornamental head lug with a cut wave pattern of the single unit type for use in bicycles from a tubular ferrous blank as a starting material by an oil hydraulic bulge forming press machine in which there are provided with a first sectional die, a second sectional die, a third sectional die, a vertically reciprocating hydraulic ram, and two horizontally opposed and reciprocating rams, the bottom half of each of said sectional die is bolted onto the bed of said press machine and the top half thereof is lowered and held in position by said vertically reciprocating ram, all of said rams are driven by the oil hydraulic pressure, the improvement which comprises inserting said tubular ferrous blank into said first sectional die designed to bulge-form a single protuberant component on said blank, subjecting said blank in said first die to the combined load of a vertical compressive load of said vertical ram, an axial compressive load applied to both ends of said blank through pistons by said horizontal rams, and a high pressure oil supplied into the interior of said blank, inserting the thus bulge formed tubular blank with one protuberant component into said second sectional die designed to form two or twin parallel small protuberant components on the exterior surface of said bulge-formed blank, the parallel direction of said twin components being located perpendicularly to the axis of said tubular blank, subjecting said primary semiproduct in said sectional die to said combined bulge forming pressure to obtain a secondary product with one and twin protuberant components on said tubular blank, inserting said secondary product into a third sectional die designed to form a ornamental joggled cut wave pattern on the exterior surface of said secondary product, mechanically forcing a pair of horizontally opposed mandrels into each end of said secondary product in said third sectional die, and forming said pattern on said surface, the outer diameter of said mandrel being bigger than the bore of said secondary product by the order of 1.5 - 2.5 mm., whereby means for eliminating repulsion resulting from the high pressure oil in said tubular blank in said first and second dies and an oil seal means by the serrated shoulder on said piston are not provided.