Cutting insert and indexable rotary cutting tool

1. A plate-shaped cutting insert that is detachably mounted in a front end portion of a tool main body that is rotated around a central axis, the cutting insert comprising:

a rake face;

a flank surface; and

a cutting edge that is formed along an intersection ridge between the rake face and the flank surface,

wherein the cutting edge includes

a bottom cutting edge that is positioned at a front end in a central axis direction and forms a convex arc shape, and

an outer peripheral cutting edge that is aligned with a radial-direction outer end of the bottom cutting edge and forms a convex arc shape of which a curvature radius is larger than that of the bottom cutting edge,

wherein an angle formed between a tangent line to a boundary point between the bottom cutting edge and the outer peripheral cutting edge and the central axis is less than 45°,

wherein a curvature radius R 1 of the bottom cutting edge is 0.3 to 10 mm, and

wherein a ratio (R 2 /R 1 ) of a curvature radius R 2 of the outer peripheral cutting edge to the curvature radius R 1 of the bottom cutting edge is 3.6 to 333.

2. The cutting insert according to claim 1 ,

wherein, when a maximum diameter of a rotation trajectory obtained when the cutting edge is rotated around the central axis is an edge diameter D, a ratio (R 1 /D) of the curvature radius R 1 of the bottom cutting edge to the edge diameter D is 0.025 to 0.1.

3. The cutting insert according to claim 1 ,

wherein, when a maximum diameter of a rotation trajectory obtained when the cutting edge is rotated around the central axis is an edge diameter D, a ratio (R 2 /D) of the curvature radius R 2 of the outer peripheral cutting edge to the edge diameter D is 1.1 to 3.5.

4. The cutting insert according to claim 1 ,

wherein a rake face of the bottom cutting edge and a rake face of the outer peripheral cutting edge are formed on the same plane.

5. The cutting insert according to claim 1 ,

wherein the cutting edge includes a linear edge that is positioned at a base end in the central axis direction and extends to be parallel to the central axis.

6. The cutting insert according to claim 5 ,

wherein the cutting edge includes a connection edge that connects the outer peripheral cutting edge and the linear edge to each other and forms a convex arc shape of which a curvature radius is smaller than that of the outer peripheral cutting edge.

7. The cutting insert according to claim 1 ,

wherein the cutting insert is formed in a front-and-rear inverse symmetric shape centered on the central axis and includes a pair of the cutting edges.

8. An indexable rotary cutting tool, comprising:

a tool main body that is rotated around a central axis;

an attaching seat that is formed in a front end portion of the tool main body in a central axis direction; and

a cutting insert that is detachably mounted in the attaching seat and includes a cutting edge,

wherein, as the cutting insert, the cutting insert according to claim 1 is used.

9. A tool main body rotated around a central axis, comprising:

an attaching seat formed in a front end portion of the tool main body in a central axis direction,

wherein a cutting insert is detachably mounted in the attaching seat and includes a cutting edge, and

wherein, as the cutting insert, the cutting insert according to claim 1 is used.