Patent ID: 7194886

Claim:
A method of forging a metallic plate member, comprising steps of: providing a first die, in which a plurality of first projections are arranged in a first direction with a fixed pitch, each of the first projections being elongated in a second direction perpendicular to the first direction; providing a second die, in which a plurality of second projections are arranged in the first direction with the fixed pitch, each of the second projections being elongated in the second direction and provided with a concave portion extending in the second direction at a distal end portion thereof; providing a third die, in which a pair of third projections arranged in the second direction and elongated in the first direction so as to define a groove therebetween, each of the third projections having a flat distal end face; opposing the first die to a first face of the plate member while opposing the second die to a second face of the plate member; performing a first forging work by sandwiching the plate member with the first die and the second die in a third direction orthogonal to the first direction and the second direction, so as to generate a plastic flow of a material in the plate member into gaps defined between the first projections while generating a plastic flow of the material into the concave portion of each of the second projection; opposing the third die to the second face of the plate member, after the first forging work; and performing a second forging work, by sandwiching the plate member with the first die and the third die in the third direction, such that the flat distal end face of each of the third projections generates a plastic flow of the material into the gaps between the first projections, while a protrusion formed on the plate member by the concave portion is received by the groove, wherein a plurality of recesses formed by the first projections are partitioned by partition walls formed by the material flown into the gaps between the first projections.