CRANK SHAFT

PURPOSE:To reduce the cost of a crank shaft by forming a hole which communicates to a main shaft member which is eccentric from a shaft center at a flange part on the main shaft side, and by weld-bonding both flange parts together through a ring shaped projection which is formed concentrically to the shaft center along the outer surface of a flange part on the crank shaft side. CONSTITUTION:A flange part 12 on the main shaft side with a shaft center c is formed at one end of a cylindrical main shaft member 11, and a communicating hole 13 which has an eccentricity 'e' from the shaft center 'c' and has a shorter diameter than a bore diameter D of the main shaft member 11 is also,formed. On the other hand, a flange 6 on the crank shaft side provided an opening 17 which communicates to the inside of a crank shaft member 15 is formed at one end thereof and a ring shaped projection 20 concentric to flange 6 is protrudedly formed along an outer surface 18. Outer surfaces 14 and 18 of the members 11 and 15, respectively, which are formed by cold forging, are abutted and connected to each other by resistance welding at the ring shaped projection 20. By this method, desired eccentricity is obtained and fluid channel is secured, and some parts can commonly be used, then the number of man-hour and a cost can be reduced.