Abstract: A method of manufacturing a die forged crankshaft to be mounted in a two or more cylinder reciprocating apparatus includes: an upsetting step that includes upsetting a billet having a constant cross-sectional area along an entire length thereof to form a blank having an enlarged cross-sectional area at a region between a portion to be formed into a leading crank arm of the crankshaft and a portion to be formed into a trailing crank arm thereof; a die forging step that includes die forging the blank formed in the upsetting step to form a forged blank having a shape of the crankshaft with a flash; and a trimming step that includes trimming the flash from the forged blank formed in the die forging step. This makes it possible to improve the material utilization and to use a billet having a cross-sectional size as small as possible.

Abstract: In a forming apparatus, journal dies hold and retain rough journal portions of a preform blank therebetween, and reference crank pin die and movable crank pin dies contact rough crank pin portions thereof. In this state, the journal dies and the movable crank pin dies are moved axially toward the reference crank pin die and the reference crank pin die and the movable crank pin dies are moved perpendicular to an axial direction. With this, rough crank arm portions are axially compressed to reduce their thickness to that of crank arms of a forged crankshaft, and the rough crank pin portions are pressed perpendicular to the axial direction to increase an amount of eccentricity to that of the forged crankshaft crank pins. Consequently, it is possible to form a blank for finish forging having a shape generally in agreement with a shape of the forged crankshaft for a three-cylinder engine.

Abstract: In a forming apparatus, stationary journal dies (10U, 10B) and movable journal dies (11U, 11B) each hold and retain rough journal portions (J?) of a preform blank (4) therebetween, and crank pin dies (12) contacts rough crank pin portions (P?) thereof, and in this state, the movable journal dies (11U, 11B) are moved axially toward the stationary journal dies (10U, 10B) and the crank pin dies (12) are moved in the same axial direction and in an eccentric direction. Rough crank arm portions (A?) are axially compressed to reduce their thickness to that of crank arms of a forged crankshaft, and the rough crank pin portions (P?) are pressed in the eccentric direction to increase eccentricity to that of the crank pins of the forged crankshaft. Consequently, it is possible to form a blank for finish forging having a shape generally in agreement with the shape of the forged crankshaft.

Abstract: In a forming apparatus, stationary journal dies (10U, 10B) and movable journal dies (11U, 11B) each hold and retain rough journal portions (J?) of a preform blank (4) therebetween, and crank pin dies (12) contacts rough crank pin portions (P?) thereof, and in this state, the movable journal dies (11U, 11B) are moved axially toward the stationary journal dies (10U, 10B) and the crank pin dies (12) are moved in the same axial direction and in an eccentric direction. Rough crank arm portions (A?) are axially compressed to reduce their thickness to that of crank arms of a forged crankshaft, and the rough crank pin portions (P?) are pressed in the eccentric direction to increase eccentricity to that of the crank pins of the forged crankshaft. Consequently, it is possible to form a blank for finish forging having a shape generally in agreement with the shape of the forged crankshaft.

Abstract: A method of manufacturing a die forged crankshaft to be mounted in a two or more cylinder reciprocating apparatus includes: an upsetting step that includes upsetting a billet having a constant cross-sectional area along an entire length thereof to form a blank having an enlarged cross-sectional area at a region between a portion to be formed into a leading crank arm of the crankshaft and a portion to be formed into a trailing crank arm thereof; a die forging step that includes die forging the blank formed in the upsetting step to form a forged blank having a shape of the crankshaft with a flash; and a trimming step that includes trimming the flash from the forged blank formed in the die forging step. This makes it possible to improve the material utilization and to use a billet having a cross-sectional size as small as possible.