To restrain the bending of a counter weight and to obtain a high precise crank shaft forged product by providing a protrusion for forming a recessed part in a burr to at least either one of an edge die.
The upper edge die 24 is provided with the protrusion 31 for forming the recessed part in the burr B3 at the deburr working time. The tensile strength in the orthogonal direction to the surface acted on the burr cut surface 32 can be reduced by cutting off the burr B3 with an edge part 26 while pushing this protrusion 31 to the burr B3. Therefore, the material flow from the forging body to the burr side is reduced, and bending of the counter weight to the axial direction can be restrained. The protrusion 31 is desirable to have the height H so as to be 0.2-0.7 times of the burr thickness T and arrange this position in the range of ≥1.0 times of the burr thickness T to ≤25 mm in the distance X between the edge part and the protrusion. Then, the normal burr thickness T is about 1-15 mm.
OHASHI MASAHIRO
OGITA TAKESHI
FUKUTOME YUKI
