Patent ID: 8657540

Claim:
A cutting insert having a polygonal plate shape comprising: a rake face having a polygonal shape with corners and a periphery; flank faces connected to the periphery of the rake face to form a peripheral border between the rake face and the flank faces; a cutting edge which is formed on the peripheral border and has a corner portion formed at one of the corners; a protruding section formed on the rake face along a bisector of the one of the corners of the rake face and apart from the corner portion of the cutting edge; and a pair of convex sections respectively formed on the rake face at both sides of the bisector so that each of said convex sections extends from the protruding section toward the cutting edge; wherein each of said convex sections has a first wall surface, a second wall surface intersecting with the first wall surface, and an intersection ridgeline between the first and second wall surfaces; each of the intersection ridgelines of the convex sections is formed to extend from a wall surface of the protruding section toward the cutting edge so that the intersection ridgelines are gradually separated from each other as they approach the corner portion of the cutting edge; the first wall surface of each convex section is formed to incline from the intersection ridgeline toward the rake face as it approaches the corner portion of the cutting edge; the second wall surface of each convex section is formed to incline from the intersection ridgeline toward the rake face as it approaches the cutting edge; the intersection ridgelines are formed to intersect with the wall surface of the protruding section at a position lower than a top portion of the protruding section; a tilt angle of the second wall surface in a cross section orthogonal to a part of the peripheral border closest to the second wall surface with respect to a direction perpendicular to the rake face is smaller than a tilt angle of the first wall surface in the cross section orthogonal to the intersection ridgelines closest to the second wall surface with respect to a direction perpendicular to the rake face the first wall surfaces are formed as an inclined flat surface; and the second wall surfaces are formed as a convex curve surface convexly curved along the intersection ridgelines; and the intersection ridgeline makes an acute angle with respect to a part of the peripheral border closest to the intersection ridgeline.