Method of manufacturing connecting rod

Abstract

An integral cast-iron connecting rod blank having a smaller-diameter end, a shank, and a larger-diameter end with a crank opening is set on an inclined base, and the tip end of a laser beam applying device is positioned in the larger-diameter end. While a YAG laser beam from the laser beam applying device is being applied to diametrically opposite inner central wall regions of the larger-diameter end, the laser beam applying device is moved to form notches transversely in the respective inner central wall regions. Two spreading elements are placed in the crank opening, and then a tapered wedge is inserted downwardly between the spreading elements. A downward impact point load is applied to a load bearing surface of the wedge thereby to apply spreading forces to the larger-diameter end. A crack starting radially outwardly from the notches is developed in the larger-diameter end, dividing the larger-diameter end into a saddle and a cap. Mating surfaces of the saddle and the cap have interfitting surface irregularities which prevent the saddle and the cap from being combined in wrong orientations. Before the larger-diameter end is split open, the crank opening is finished for roundness while the larger-diameter end is being subjected to the same load as a fastening load by which the saddle and the cap will be fastened by bolts.