Cutting insert with a linear and a concave cutting edge portion

1. A cutting insert, comprising:

a top face;

a bottom face, wherein a central axis of the cutting insert extends through the top face and the bottom face;

a plurality of side walls extending between the top face and the bottom face;

a peripheral cutting edge defined at the juncture of each side wall and the top face, each cutting edge including a linear cutting edge portion and a concave cutting edge portion, wherein the concave cutting edge portion is a curved edge that curves inwardly in a plane that is perpendicular to a plane containing the central axis; and

a radiused corner portion connecting two adjacent cutting edges, wherein each linear cutting edge portion extends from one radiused corner portion to the concave cutting edge portion and each concave cutting edge portion extends from the linear cutting edge portion to another radiused corner portion.

2. The cutting insert of claim 1 , wherein each side wall includes a flat side wall portion adjacent the linear cutting edge portion.

3. The cutting insert of claim 2 , wherein each side wall further includes a concave side wall portion adjacent the concave cutting edge portion.

4. The cutting insert of claim 3 , wherein the concave side wall portion has a radius that is substantially the same as a radius of the concave cutting edge portion.

5. The cutting insert of claim 3 , further including a rounded corner side wall adjacent each radiused corner portion, wherein the rounded corner side wall connects the concave side wall portion of one side wall with a flat side wall portion of the adjacent side wall.

6. The cutting insert of claim 1 , wherein the concave cutting edge portion has a greater length than the linear cutting edge portion.

7. The cutting insert of claim 1 , wherein the concave cutting edge portion has a length in the range of about 1 mm to about 30 mm.

8. The cutting insert of claim 1 , wherein the linear cutting edge portion has a length in the range of about 0.1 mm to about 12 mm.

9. The cutting insert of claim 1 , wherein the concave cutting edge portion has a radius in the range of about 1 mm to about 100 mm.

10. The cutting insert of claim 1 , wherein the top face includes a chip breaking groove formed therein and extending alongside the cutting edges, the chip-breaking groove including a descending wall which inclines downwardly from the cutting edges to a bottom area of the chip breaking groove and a back wall which inclines upwardly from the bottom area of the chip breaking groove.

11. The cutting insert of claim 10 , wherein the back wall of the chip breaking groove extends upwardly to a raised central top surface of the top face of the cutting insert.

12. The cutting insert of claim 11 , wherein the raised central top surface defines a mounting opening that extends axially through the cutting insert.

13. The cutting insert of claim 1 , wherein the linear cutting edge portion and the concave cutting edge portion each include top portions that are contained in the same plane.

14. A cutting insert, comprising:

an indexable, polygonal insert body having a top face, an opposing bottom seating surface and a plurality of side walls extending between the top face and the bottom seating surface;

a peripheral cutting edge defined at the intersection of each side wall and the top face, each cutting edge including a linear cutting edge portion and a concave cutting edge portion that has a greater length than the linear cutting edge portion, wherein the concave cutting edge portion is a curved edge that curves inwardly in a plane that is perpendicular to a plane containing a central axis of the cutting insert that extends through the top face and the bottom seating surface; and

the insert body further includes a radiused corner portion connecting two adjacent cutting edges, wherein each linear cutting edge portion extends from one radiused corner portion to the concave cutting edge portion and the concave cutting edge portion extends from the linear cutting edge portion to another radiused corner portion.

15. The cutting insert of claim 14 , wherein each side wall includes a flat side wall portion adjacent the straight cutting edge portion and a concave side wall portion adjacent the concave cutting edge portion.

16. The cutting insert of claim 14 , wherein the linear cutting edge portion and the concave cutting edge portion each include top portions that are contained in the same plane.

17. A drilling tool, comprising:

a tool body having an axial rearward end having a shank portion and an axial forward end that defines an insert pocket; and

a cutting insert structured and arranged to be removably received in the insert pocket of the tool body, the cutting insert comprising:

a top face;

a bottom seating surface, wherein a central axis of the cutting insert passes through the top face and the bottom seating surface;

a plurality of side walls extending between the top face and the bottom seating surface;

a peripheral cutting edge defined at the juncture of each side wall and the top face, each cutting edge including a linear cutting edge portion and a concave cutting edge portion, wherein the concave cutting edge portion is a curved edge that curves inwardly in a plane that is perpendicular to a plane containing the central axis; and

a radiused corner portion connecting two adjacent cutting edges, wherein each linear cutting edge portion extends from one radiused corner portion to the concave cutting edge portion and each concave cutting edge portion extends from the linear cutting edge portion to another radiused corner portion.

18. The drilling tool of claim 17 , wherein each side wall includes a flat side wall portion adjacent the straight cutting edge portion and a concave side wall portion adjacent the concave cutting edge portion.

19. The drilling tool of claim 17 , wherein the linear cutting edge portion and the concave cutting edge portion each include top portions that are contained in the same plane.