Billet for cold forging, method of manufacturing billet for cold forging, method of continuously cold-forging billet, method of cold-forging

A method of manufacturing a billet for cold forging, wherein the steps of quenching a blank unloaded from a heating furnace to form a fine martensitic structure in a surface thereof, and then annealing the blank to convert the martensitic structure of the surface into a fine spherodized structure comprising ferrite and cementite.

A method of cold-forging a crankshaft from a billet formed by continuous cold forging, wherein the first step of extruding the billet to form a multi-stepped shaft having at least two steps and contiguous to a main body, the second step of upsetting and drawing the formed work piece to simultaneously increase the diameter of the main body and reduce the diameter of at least a portion of the multi-stepped shaft, the third step of upsetting and drawing the formed work piece to simultaneously rough the main body to an asymmetrical shape and reduce the diameter of at least a portion of the multi-stepped shaft, the fourth step of pressing an asymmetrical boundary of the main body to simultaneously finish the main body and form a central hole axially centrally in the main body, and the fifth step of forming a pin hole in the main body at a predetermined position and removing an outer circumferential portion of the main body thereby to shape the main body.

A method of cold-forging a disk-shaped part with a shaft from a multi-stepped intermediate blank through a plurality of forging steps, characterized by forming an asymmetrical disk having left and right portions of different volumes with respect to an axial center of said intermediate blank.

A method of cold-forming a crankshaft, wherein continuously cold-forming a blank mad of carbon steel, which is composed of 0.46-0.48 wt % of C (carbon), 0.14 or less of Si (silicon), 0.55-0.65 wt % of Mn (manganese), 0.015 wt % or less of P (phosphorus), 0.015 wt % or less of S (sulfur), 0.15 wt % or less of Cu (copper), 0.20 wt % or less of Ni (nickel), 0.35 wt % or less of Cr (chromium), and a remainder of Fe (iron) and impurities, thereby to produce a crankshaft, and thereafter aging the crankshaft.

A method of cold-forging a crankshaft, wherein the first spherodizing annealing step of spherodizing a blank made of a carbon steel which is composed of 0.46-0.48 wt % of C (carbon), 0.14 or less of Si (silicon), 0.55-0.65 wt % of Mn (manganese), 0.015 wt % or less of P (phosphorus), 0.015 wt % or less of S (sulfur), 0.15 wt % or less of Cu (copper), 0.20 wt % or less of Ni (nickel), 0.35 wt % or less of Cr (chromium), and a remainder of Fe (iron) and impurities, the drawing step of drawing the blank at a predetermined sectional area reduction ratio after the first spherodizing annealing step, the second spherodizing annealing step of promoting the dispersion of an internal carbide of an increased spherodizing ratio after the drawing step thereby to produce a billet, continuously cold-forming the billet into a crankshaft, and thereafter aging the crankshaft.

A method of cold-forging a disk-shaped part with a shaft, characterized by holding the shaft of the cold-forged disk-shaped part with a lower support base of a forming die, lowering an upper die assembly to hold the disk of the disk-shaped part between the lower support base and an upper support base and lower the disk-shaped part by a predetermined stroke, punching a hole in a predetermined region of the disk with a punch of a lower die assembly, and thereafter lowering the upper die assembly to cause an upper die to remove an outer circumferential portion of the disk.