Cutting insert and indexable rotary cutting tool

1. A cutting insert, comprising:

a first end surface and a second end surface facing opposite to each other;

a peripheral side surface extending between the first end surface and the second end surface; and

a cutting edge formed at an intersecting ridge portion between the first end surface and the peripheral side surface, the cutting edge being formed so that the first end surface functions as a rake face and a part of the peripheral side surface functions as a flank, wherein

a portion of the peripheral side surface adjacent to at least a part of the cutting edge includes at least a first flank portion adjacent to the cutting edge, a second flank portion, a third flank portion, and a fourth flank portion, which are arranged in this order from a side of the first end surface toward a side of the second end surface, wherein

the first flank portion has a slope angle that gradually varies along the cutting edge, and a width that is constant or substantially constant in an area along the cutting edge from the side of the first end surface toward the side of the second end surface;

the slope angle of the first flank portion has a minimum value that falls in a range of not less than 2.0° and not more than 6.0°, and the slope angle of the first flank portion has a maximum value that falls in a range of not less than 10.5° and not more than 14.5°;

the second flank portion connects the first flank portion and the third flank portion, the second flank portion has a slope angle resulting in the second flank portion being angled toward a central axis (A) in a direction from the first flank portion toward the third flank portion;

a slope angle of the third flank portion falls in a range of not less than 0.0° and not more than 11.0°; and

the fourth flank portion has a slope angle greater than the third flank portion.

2. The cutting insert according to claim 1 , wherein

the width of the first flank portion falls in a range of not less than 0.1 mm and not more than 0.6 mm.

3. The cutting insert according to claim 1 , wherein

an inscribed circle (IC) is settable in the first end surface when the cutting insert is viewed from a side opposite to the first end surface; and

a ratio of the diameter of the inscribed circle relative to the thickness of the cutting insert is not less than 1.5 and not more than 2.2.

4. The cutting insert according to claim 1 , wherein

the second end surface is formed so as to function as a seating surface when the cutting insert is mounted to a tool body; and

the second end surface is provided with at least three projections.

5. The cutting insert according to claim 1 , wherein

the cutting edge includes a major cutting edge, an minor cutting edge, and a corner cutting edge connecting the major cutting edge and the minor cutting edge; and

the first flank portion is adjacent to at least the major cutting edge.

6. The cutting insert according to claim 5 , wherein

the major cutting edge is formed so as to gradually approach the second end surface with an increasing distance from the corner cutting edge.

7. The cutting insert according to claim 5 , wherein

the first flank portion is formed so that the slope angle gradually increases with an increasing distance from the corner cutting edge along the major cutting edge.

8. The cutting insert ( 1 ) according to claim 1 , wherein

an outline shape of the cutting insert is substantially triangular when the cutting insert is viewed from a side opposite to the first end surface, and the cutting insert includes the three cutting edges.

9. An indexable rotary cutting tool comprising a tool body having at least one insert mounting seat at a leading end portion, with a cutting insert being detachably mounted on the insert mounting seat, wherein

the cutting insert is a cutting insert according to claim 1 ;

the cutting insert is mounted on the insert mounting seat with an axial rake falling in a range of not less than 6° and not more than 14° and a radial rake falling in a range of not less than −8° and not more than 0°; and

a relief angle of the first flank portion of the cutting insert mounted on the insert mounting seat is not less than 5° and not more than 13°.

10. The indexable rotary cutting tool according to claim 9 , wherein:

the insert mounting seat has first and second side wall surfaces;

neither the first nor second flank portions of the peripheral side surface are in abutment with the first and second sidewalls; and

only the third flank portions of the peripheral side surface are in abutment with the sidewall surface of the insert mounting seat.

11. The cutting insert according to claim 1 , wherein only the third flank portion comprises an abutment surface configured to abut a side wall of an insert mounting seat.

12. The cutting insert according to claim 1 , wherein each of the slope angles of the first to fourth flank portions is defined on a first plane (P 3 ) that is set in parallel to the central axis (A) and forms a right angle with respect to the cutting edge,

wherein, each of the slope angles of the first to fourth flank portions is defined with respect to a second plane (P 4 ), which passes through an intersecting portion between the cutting edge and the first plane, is perpendicular to the first plane, and is parallel to the central axis,

wherein, the second plane only intersects the cutting insert at the cutting edge.

13. A cutting insert, comprising:

a first end surface and a second end surface facing opposite to each other;

a peripheral side surface extending between the first end surface and the second end surface; and

a cutting edge formed at an intersecting ridge portion between the first end surface and the peripheral side surface, the cutting edge being formed so that the first end surface functions as a rake face and a part of the peripheral side surface functions as a flank, wherein

a portion of the peripheral side surface adjacent to at least a part of the cutting edge includes at least a first flank portion adjacent to the cutting edge, a second flank portion, a third flank portion, and a fourth flank portion, which are arranged in this order from a side of the first end surface toward a side of the second end surface, wherein

the first flank portion has a slope angle that gradually varies along the cutting edge, and a width that is constant or substantially constant in an area along the cutting edge from the side of the first end surface toward the side of the second end surface;

the slope angle of the first flank portion has a minimum value that falls in a range of not less than 2.0° and not more than 6.0°, and the slope angle of the first flank portion has a maximum value that falls in a range of not less than 10.5° and not more than 14.5°;

the second flank portion connects the first flank portion and the third flank portion;

a slope angle of the third flank portion falls in a range of not less than 0.0° and not more than 11.0°; and

the fourth flank portion has a slope angle greater than the third flank portion;

wherein, each of the slope angles of the first to fourth flank portions is defined on a first plane (P 3 ) that is set in parallel to a central axis (A) and forms a right angle with respect to the cutting edge,

wherein, each of the slope angles of the first to fourth flank portions is defined with respect to a second plane (P 4 ), which passes through the intersecting portion between the cutting edge and the first plane, is perpendicular to the first plane, and is parallel to the central axis A, and

wherein, the second plane only intersects the cutting insert at the cutting edge.

14. The cutting insert according to claim 13 , wherein

the width of the first flank portion falls in a range of not less than 0.1 mm and not more than 0.6 mm.

15. The cutting insert according to claim 13 , wherein

an inscribed circle (IC) is settable in the first end surface when the cutting insert is viewed from a side opposite to the first end surface; and

a ratio of the diameter of the inscribed circle relative to the thickness of the cutting insert is not less than 1.5 and not more than 2.2.

16. The cutting insert according to claim 13 , wherein

the second end surface is formed so as to function as a seating surface when the cutting insert is mounted to a tool body; and

the second end surface is provided with at least three projections.

17. The cutting insert according to claim 13 , wherein

the cutting edge includes a major cutting edge, an minor cutting edge, and a corner cutting edge connecting the major cutting edge and the minor cutting edge; and

the first flank portion is adjacent to at least the major cutting edge.

18. The cutting insert according to claim 17 , wherein

the major cutting edge is formed so as to gradually approach the second end surface with an increasing distance from the corner cutting edge.

19. The cutting insert according to claim 17 , wherein

the first flank portion is formed so that the slope angle gradually increases with an increasing distance from the corner cutting edge along the major cutting edge.

20. The cutting insert according to claim 13 , wherein

an outline shape of the cutting insert is substantially triangular when the cutting insert is viewed from a side opposite to the first end surface, and the cutting insert includes the three cutting edges.