Cutting insert, cutting tool, and method for manufacturing machined product

1. A cutting insert comprising:

a top surface comprising a corner portion and a pair of side portions each adjacent to the corner portion;

a bottom surface;

a side surface located between the top surface and the bottom surface; and

a corner cutting edge disposed at the corner portion; wherein

the top surface comprises

a first rake surface located along the corner cutting edge,

a raised portion located farther to an inner side than the first rake surface and projecting in an upward direction, and

a second rake surface located between the corner cutting edge and the raised portion and recessed with respect to the first rake surface, and

a rake angle at a first region of the second rake surface corresponding to a center of the corner cutting edge is greater than a rake angle at a second region of the second rake surface located beside the first region.

2. The cutting insert according to claim 1 , wherein a rake angle at the second rake surface decreases from the first region toward end regions of the second region corresponding to both end portions of the corner cutting edge.

3. The cutting insert according to claim 1 , wherein, of a width of the corner cutting edge and a width of the second rake surface in a direction orthogonal to a bisecting line of the corner cutting edge in a top view, the width of the corner cutting edge is greater than the width of the second rake surface.

4. The cutting insert according to claim 3 , further comprising:

a minor cutting edge disposed on a side portion of the pair of side portions of the top surface; wherein

an end portion of the second rake surface is located on the top surface and on an inner side of a boundary portion between the corner cutting edge and the minor cutting edge in a direction orthogonal to the cutting edge in a top view.

5. The cutting insert according to claim 1 , wherein a portion of an outer peripheral edge of the second rake surface facing the corner cutting edge has a convex curved shape projecting toward the corner cutting edge in a top view.

6. The cutting insert according to claim 5 , wherein the portion of the outer peripheral edge of the second rake surface facing the corner cutting edge has an arc shape in a top view.

7. The cutting insert according to claim 1 , wherein, in a cross-section orthogonal to the corner cutting edge and including a bisecting line of the corner cutting edge, a bottom portion of the second rake surface has a concave curved shape.

8. The cutting insert according to claim 1 , wherein a height from the bottom surface of a lower end of the second rake surface increases toward positions corresponding to both end portions of the corner cutting edge from a position corresponding to a center of the corner cutting edge.

9. The cutting insert according to claim 1 , wherein a rake angle at the first rake surface is constant from a position corresponding to a center of the corner cutting edge to positions corresponding to both end portions of the corner cutting edge.

10. A cutting tool comprising:

a holder comprising an insert pocket on a leading end thereof; and

the cutting insert according to claim 1 , mounted on the insert pocket with the corner cutting edge protruding from the leading end of the holder.

11. A method for manufacturing a machined product, the method comprising:

rotating a work material;

bringing the corner cutting edge of the cutting tool according to claim 10 into contact with the work material that is rotating; and

separating the cutting tool from the work material that is rotating.