An apparatus for manufacturing a forged crankshaft includes a pair of upper and lower dies and a first tool. The pair of dies deforms first excess portions and thereby thickens both side portions of a rough crank arm, in a region near a rough pin adjacent thereto. The first tool is fitted in an open space made in the pair of dies, and is capable of coming into contact with a rough-journal-facing surface of the rough crank arm, except the side portions in the region near the adjacent rough pin. The first pair of dies and the first tool have first guides to guide the first tool from a retracting position to a contacting position. The first guides include a first guide disposed on at least one of an upper surface and a lower surface of the first tool.

An apparatus for manufacturing a forged crankshaft includes a pair of upper and lower dies and a first tool. The pair of dies deforms first excess portions and thereby thickens both side portions of a rough crank arm, in a region near a rough pin adjacent thereto. The first tool is fitted in an open space made in the pair of dies, and is capable of coming into contact with a rough-journal-facing surface of the rough crank arm, except the side portions in the region near the adjacent rough pin. The first pair of dies and the first tool have first guides to guide the first tool from a retracting position to a contacting position. The first guides include a first guide disposed on at least one of an upper surface and a lower surface of the first tool.

A method of manufacturing a crankshaft includes the steps of: (1) forming a crankshaft blank via a first half and a second half; (2) measuring a plurality of surface variations between a predetermined surface in a first region and a corresponding predetermined surface in a second region of the crankshaft blank; (3) calculating centering offset data based on the plurality of surface variations; (4) machining a pair center holes based on the centering offset data; (5) machining a counterweight and a journal relative to the pair of center holes to produce a partially machined crankshaft; (5) milling and grinding the partially machined crankshaft to produce a finished machined crankshaft; and (6) rotating the finished machined crankshaft typically on the outermost main journals in a final balancing machine and then modifying the counterweights to eliminate undesirable vibration generated during the rotation and engine operation.

A method of manufacturing a crankshaft includes the steps of: (1) forming a crankshaft blank via a first half and a second half; (2) measuring a plurality of surface variations between a predetermined surface in a first region and a corresponding predetermined surface in a second region of the crankshaft blank; (3) calculating centering offset data based on the plurality of surface variations; (4) machining a pair center holes based on the centering offset data; (5) machining a counterweight and a journal relative to the pair of center holes to produce a partially machined crankshaft; (5) milling and grinding the partially machined crankshaft to produce a finished machined crankshaft; and (6) rotating the finished machined crankshaft typically on the outermost main journals in a final balancing machine and then modifying the counterweights to eliminate undesirable vibration generated during the rotation and engine operation.

A production method includes a preforming process, a forming process and a finish forging process. In the preforming process, an intermediate preform is formed from a billet. In the forming process, while each of a plurality of rough journals of the intermediate preform is held and pressed vertically by a pair of holding dies, rough pins are decentered in directions perpendicular to the pressing direction by the holding dies and an axial direction of the intermediate preform, and the intermediate preform is pressed in the axial direction of the intermediate preform. In the finish forging process, a final preform is placed such that the directions in which the rough pins are decentered are parallel to a horizontal direction, and the thus placed final preform is pressed vertically by a pair of pressing dies. The production method reduces the risk of occurrence of seams on a forged crankshaft.

A production method includes a preforming process, a forming process and a finish forging process. In the preforming process, an intermediate preform is formed from a billet. In the forming process, while each of a plurality of rough journals of the intermediate preform is held and pressed vertically by a pair of holding dies, rough pins are decentered in directions perpendicular to the pressing direction by the holding dies and an axial direction of the intermediate preform, and the intermediate preform is pressed in the axial direction of the intermediate preform. In the finish forging process, a final preform is placed such that the directions in which the rough pins are decentered are parallel to a horizontal direction, and the thus placed final preform is pressed vertically by a pair of pressing dies. The production method reduces the risk of occurrence of seams on a forged crankshaft.

A production method includes a preforming process, a forming process and a finish forging process. In the preforming process, an intermediate preform is formed from a billet. In the forming process, while each of a plurality of rough journals of the intermediate preform is held and pressed vertically by a pair of holding dies, rough pins are decentered in directions perpendicular to the pressing direction by the holding dies and an axial direction of the intermediate preform, and the intermediate preform is pressed in the axial direction of the intermediate preform. In the finish forging process, a final preform is placed such that the directions in which the rough pins are decentered are parallel to a horizontal direction, and the thus placed final preform is pressed vertically by a pair of pressing dies. The production method reduces the risk of occurrence of seams on a forged crankshaft.

A production method includes a preforming process, a forming process and a finish forging process. In the preforming process, an intermediate preform is formed from a billet. In the forming process, while each of a plurality of rough journals of the intermediate preform is held and pressed vertically by a pair of holding dies, rough pins are decentered in directions perpendicular to the pressing direction by the holding dies and an axial direction of the intermediate preform, and the intermediate preform is pressed in the axial direction of the intermediate preform. In the finish forging process, a final preform is placed such that the directions in which the rough pins are decentered are parallel to a horizontal direction, and the thus placed final preform is pressed vertically by a pair of pressing dies. The production method reduces the risk of occurrence of seams on a forged crankshaft.

A cutter performs milling on a crankshaft blank having a journal and a counterweight coupled to the journal. The cutter includes an annular main body part, a first chip, and a second chip. The annular main body part is centered on a predetermined axis center. The first chip is attached to a circumferential surface of the main body part and is used to cut an external circumferential surface of the journal. The second chip is attached to the circumferential surface of the main body part and is used to cut a groove on the external circumferential surface of the journal.

A cutter performs milling on a crankshaft blank having a journal and a counterweight coupled to the journal. The cutter includes an annular main body part, a first chip, and a second chip. The annular main body part is centered on a predetermined axis center. The first chip is attached to a circumferential surface of the main body part and is used to cut an external circumferential surface of the journal. The second chip is attached to the circumferential surface of the main body part and is used to cut a groove on the external circumferential surface of the journal.