A multi-diameter tubular body is cold-forged by forming a large-diameter hole portion in a formed body having a preliminary hole through subjection of the preliminary hole to deep hole forming and by punching out the bottom surface of the large-diameter hole portion to thereby form a small-diameter hole portion. Since a punch having a central protrusion on its forward end surface is used, an internal flaw is generated by dead metal in the inner circumferential surface of a depression, formed by the protrusion, in the bottom surface of the large-diameter hole portion. An outside diameter of a protrusion of a deep hole forming punch is rendered smaller than an inside diameter of the small-diameter hole portion to be formed later by punching out the bottom surface of the large-diameter hole portion. As a result, the internal flaw is removed when the small-diameter hole portion is formed.

A piercing die, a holding body, and a piercing punch are used to form a pressed component having a plate-shaped base portion and a tubular boss portion extending from the base portion. The piercing die has a receiving portion, an outer shape-forming portion, and a die-side cutting edge. The piercing punch has an inner shape-forming portion, a punch-side cutting edge, and a straight portion. In a process of forming a pressed component, the piercing punch is pressed against a preform which is formed from a blank and which has a preliminary boss portion so as to cause part of the preliminary boss portion to flow toward the outer shape-forming portion, and so as to then cut off another part of the preliminary boss portion to form a boss portion.

A piercing die, a holding body, and a piercing punch are used to form a pressed component having a plate-shaped base portion and a tubular boss portion extending from the base portion. The piercing die has a receiving portion, an outer shape-forming portion, and a die-side cutting edge. The piercing punch has an inner shape-forming portion, a punch-side cutting edge, and a straight portion. In a process of forming a pressed component, the piercing punch is pressed against a preform which is formed from a blank and which has a preliminary boss portion so as to cause part of the preliminary boss portion to flow toward the outer shape-forming portion, and so as to then cut off another part of the preliminary boss portion to form a boss portion.

An annular reference surface is formed around a through-hole of an eye portion. A distal-end-side curved portion is formed at a first corner portion, on an outer side of the annular reference surface. The thickness of the distal-end-side curved portion is reduced in a range of a length from the first flat surface toward the distal end surface. A hole-side curved portion whose thickness is reduced toward an inner surface of the through-hole is formed at a second corner portion, on an inner side of the annular reference surface. The length of the hole-side curved portion is less than the length of the distal-end-side curved portion. The hole-side curved portion is curved with a greater curvature than that of the distal-end-side curved portion.

A method of manufacturing a light rotor shaft for eco-friendly vehicles is provided which includes cutting a pipe material in a specified length to provide a pipe blank and forming the pipe blank to provide a first form having the first segment on a first side. The method further includes, forming a second form having the second segment by inserting and rotating a first side of a mandrel into the first side of the first form and concurrently hammer-forging the second side of the first form to form the second segment. The rotor shaft includes a third segment formed by inserting and rotating the second side of the mandrel into the first side of the second form to form the third segment.

A method of manufacturing a light rotor shaft for eco-friendly vehicles is provided which includes cutting a pipe material in a specified length to provide a pipe blank and forming the pipe blank to provide a first form having the first segment on a first side. The method further includes, forming a second form having the second segment by inserting and rotating a first side of a mandrel into the first side of the first form and concurrently hammer-forging the second side of the first form to form the second segment. The rotor shaft includes a third segment formed by inserting and rotating the second side of the mandrel into the first side of the second form to form the third segment.

A hollow forging process for main shaft of large wind turbine generator, wherein, comprising the following steps as: the first step of cutting off the dead head and the bottom of an ingot; the second step of upsetting and punching a hole; the third step of drawing-out; and the fourth step of local upsetting, drawing-out and shaping-up. In the fourth step, the forged piece is shaped up by local upsetting and drawing-out through a turnplate. The hollow forging process for main shaft created by the invention can save the costs for enterprise to purchase large equipment and makes it possible to forge the main shaft of large wind turbine generator with a free forging oil press with a smaller size.

A system and method of making a forged part. A flange may be forged between first and second ends of the part by actuating an upset punch against a second end of the tube that is disposed opposite the first end. The flange may extend away from an axis along which an upset punch is actuated.

A system and method of making a forged part. A flange may be forged between first and second ends of the part by actuating an upset punch against a second end of the tube that is disposed opposite the first end. The flange may extend away from an axis along which an upset punch is actuated.

A method of manufacturing a light rotor shaft for eco-friendly vehicles is provided which includes cutting a pipe material in a specified length to provide a pipe blank and forming the pipe blank to provide a first form having the first segment on a first side. The method further includes, forming a second form having the second segment by inserting and rotating a first side of a mandrel into the first side of the first form and concurrently hammer-forging the second side of the first form to form the second segment. The rotor shaft includes a third segment formed by inserting and rotating the second side of the mandrel into the first side of the second form to form the third segment.