PTL 1 describes an example of the above-described cutting insert according to the related art. The cutting insert disclosed in PTL 1 includes a substrate having a seat at a corner thereof, the seat being recessed from the top surface of the substrate. A superhard sintered body is bonded to the seat, and a cutting edge, a rake face, and a chip breaker are formed in the superhard sintered body.
In the cutting insert according to PTL 1, a relatively large negative rake face is formed along edges of the top surface of the substrate and the superhard sintered body. A flat land, which functions as a rake face, is formed in the superhard sintered body by removing a corner of the superhard sintered body along a ridge line that function as a cutting edge at a position such that the negative rake face somewhat remains. A chip breaker is formed by cutting the superhard sintered body obliquely upward from an end of the land.
The chip breaker includes a projection that projects from the position of the negative rake face toward a tip end of an arc edge such that the amount of projection is at a maximum at the center thereof and a breaker wall that extends obliquely upward from the rake face toward a top edge of the projection. The breaker wall includes two surfaces that are connected to each other at an angle.