Forged crankshaft and method for manufacturing the forged crankshaft

Patent metadata

Field	Value
Publication number	US-9731341-B2
Application number	US-201314647472-A
Country	US
Kind code	B2
Filing date	Dec 9, 2013
Priority date	Dec 12, 2012
Publication date	Aug 15, 2017
Grant date	Aug 15, 2017

Abstract

A forged crankshaft ( 1 ) includes a carbon steel containing S, wherein in a portion corresponding to a machined outer circumferential surface of a shaft part such as journals (J), crank pins (P), a front part (Fr), and a flange (Fl), a ratio x/y of an area rate x of sulfide in a position (X) corresponding to a parting surface of a die for finish forging to an area rate y of sulfide in a position (Y) corresponding to a bottom of a die impression of the die for finish forging is equal to or lower than 1.5. The forged crankshaft ( 1 ) can avoid an occurrence of machined surface cracks on the journals (J) and the crank pins (P) after the outer circumferential surface is machined.

First claim

What is claimed is:

1. A forged crankshaft, comprising:
a carbon steel containing sulfide,
wherein in a portion corresponding to a machined outer circumferential surface of a shaft part, a ratio x/y of an area rate x of sulfide in a position corresponding to a parting surface of a die for finish forging to an area rate y of sulfide in a position corresponding to a bottom of a die impression of the die for finish forging is equal to or lower than 1.5.

2. The forged crankshaft according to claim 1 comprising the carbon steel containing C of 0.30% to 0.60% by mass and S of 0.01% to 0.30% by mass.

3. The forged crankshaft according to claim 1 being a forged crankshaft for a multiple cylinder engine.

4. A method for manufacturing the forged crankshaft according to claim 3 , comprising the successive steps of:
a first preforming step for forming a preform blank having a crankshaft shape, the preform blank formed to include: 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 having a smaller amount of eccentricity in an eccentric direction perpendicular to the axial direction than an amount of eccentricity of the 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;
a second preforming step for forming a blank for finish forging by using a forming apparatus, the forming apparatus including stationary journal dies, movable journal dies, and crank pin dies:
the stationary journal dies disposed at locations corresponding to a location of one of the rough journal portions of the preform blank, and the stationary journal dies configured to hold and retain the rough journal portion therebetween in the eccentric direction perpendicular to the axial direction, while being in contact with side surfaces of corresponding ones of the rough crank arm portions, the corresponding ones of the rough crank arm portions connecting with the rough journal portion;
the movable journal dies disposed at locations corresponding to locations of the rough journal portions excluding the rough journal portion to be held by the stationary journal dies, and the movable journal dies configured to hold and retain the rough journal portions therebetween in the eccentric direction perpendicular to the axial direction, and configured to move axially toward the stationary journal dies, while being in contact with side surfaces of corresponding ones of the rough crank arm portions, the corresponding ones of the rough crank arm portions each connecting with a corresponding one of the rough journal portions; and
the crank pin dies disposed at locations corresponding to locations of the rough crank pin portions, and the crank pin dies configured to be brought into contact with the respective rough crank pin portions at inner sides thereof, and configured to move axially toward the stationary journal dies and in the eccentric direction perpendicular to the axial direction while being in contact with side surfaces of corresponding ones of the rough crank arm portions, the corresponding ones of the rough crank arm portions each connecting with a corresponding one of the rough crank pin portions,
in the second preforming step where the rough journal portions are held and retained by the stationary journal dies and the movable journal dies, the rough crank pin portions are contacted by the crank pin dies, the movable journal dies are moved axially, and the crank pin dies are moved axially and in the eccentric 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 eccentric direction so as to increase the amount of eccentricity thereof to the amount of eccentricity of the crank pins of the forged crankshaft; and
a finish forging step for finish forging the blank for finish forging by using a pair of upper and lower dies to form a finished blank in which a final shape of the forged crankshaft is formed.

Assignees

• Nippon Steel & Sumitomo Metal Corp

Inventors

• Tahira Hiroaki
• Kim Kisung
• Okubo Junichi

Classifications

• F16C2204/64

  Medium carbon steel, i.e. carbon content from 0.4 to 0,8 wt% · CPC title

• F16C2220/46

  by forging · CPC title

• F16C3/08

  made in one piece (features relating to lubrication F16C3/14, to cooling F16C3/16) · CPC title

• B21J5/12

  Forming profiles on internal or external surfaces (making screw-thread by forging, pressing, or hammering B21K) · CPC title

• B21J5/025

  Closed die forging · CPC title