Apparatus for forming a blank for finish forging for a forged crankshaft for a three-cylinder engine and method for manufacturing a forged crankshaft for a three-cylinder engine using the same

An apparatus for forming a blank for finish forging for a forged crankshaft for a three-cylinder engine, the apparatus configured to form, in a process of manufacturing the forged crankshaft, the blank for finish forging to be subjected to finish forging by which a final shape of the forged crankshaft is obtained,

• the apparatus configured to form the blank for finish forging from a preform blank, the preform blank including the following elements spaced along an axial direction:
• rough journal portions having an axial length equal to an axial length of journals of the forged crankshaft;
• rough crank pin portions having an axial length equal to an axial length of crank pins of the forged crankshaft;
• and rough crank arm portions having an axial thickness greater than an axial thickness of crank arms of the forged crankshaft, wherein the rough crank pin portions are separated from each other by corresponding rough journal portions and rough crank arm portions
• the rough crank pin portions of the preform blank having a smaller amount of eccentricity in a direction perpendicular to an axial direction than an amount of eccentricity of the crank pins of the forged crankshaft,
• the apparatus, comprising:
• a reference crank pin die disposed at a location of one rough crank pin portion among the rough crank pin portions located at a center of the preform blank, the reference crank pin die configured to be brought into contact with such one rough crank pin portion, the reference crank pin die configured to move in the direction perpendicular to the axial direction, but be constrained from moving axially, while being in contact with side surfaces of rough crank arm portions through which the rough crank arm portions connect with such one rough crank pin portion;
• movable crank pin dies disposed at locations of the corresponding rough crank pin portions at opposite sides of the reference crank pin die on the preform blank and excluding the rough crank pin portion being in contact with the reference crank pin die, the movable crank pin dies configured to be brought into contact with such rough crank pin portions, the movable crank pin dies configured to move axially toward the reference crank pin die and in the direction perpendicular to the axial direction, while being in contact with side surfaces of the rough crank arm portions through which the rough crank arm portions connect with such rough crank pin portions;
• and
• journal dies disposed at locations of the corresponding rough journal portions, the journal dies configured to hold and retain such rough journal portions therebetween in the direction perpendicular to the axial direction, the journal dies configured to move axially toward the reference crank pin die while being in contact with side surfaces of the rough crank arm portions through which the rough crank arm portions connect with such rough journal portions,
• wherein, in a state where the rough journal portions are held and retained by the journal dies, and the rough crank pin portions are contacted by the reference crank pin die and the movable crank pin dies, the journal dies are configured to be moved axially, the movable crank pin dies are configured to be moved axially and in the direction perpendicular to the axial direction, and the reference crank pin die is configured to be moved in the direction perpendicular to the axial direction, thereby compressing the rough crank arm portions in the axial direction so as to reduce the thickness thereof to the thickness of the crank arms of the forged crankshaft, and pressing the rough crank pin portions in the direction perpendicular to the axial direction so as to increase the amount of eccentricity thereof to the amount of eccentricity of the crank pins of the forged crankshaft.