Cutting insert, cutting tool, and method of manufacturing machined product using the same

A cutting insert, comprising:

• a polygonal shaped upper surface;
• a lower surface being identical in shape to the upper surface;
• a side surface connected to each of the upper surface and the lower surface;
• and
• an upper cutting edge located at an intersection of the upper surface and the side surface, wherein
• the upper surface comprises first and second corners adjacent to each other, and a rake surface continuous with the upper cutting edge,
• the upper cutting edge comprises, sequentially from the first corner to the second corner, a corner cutting edge, a minor cutting edge inclined as separating from the corner cutting edge at a first inclination angle on a basis of a vertical plane perpendicular to a central axis extending between the upper and lower surfaces, and a major cutting edge inclined as separating from the minor cutting edge at a second inclination angle on the basis of the vertical plane so as to become more closer to the lower surface than the minor cutting edge, and
• the rake surface comprises a minor rake surface being continuous with the minor cutting edge and inclined as going inward at a first rake angle on the basis of the vertical plane so as to approach the lower surface, and a major rake surface being continuous with the major cutting edge and inclined as going inward at a second rake angle on the basis of the vertical plane so as to approach the lower surface, wherein the first rake angle of the minor rake surface is larger at an end portion thereof located closer to the second corner than that at an end portion thereof located closer to the first corner, and the second rake angle of the major rake surface is larger at an end portion thereof located closer to the first corner than that at an end portion thereof located closer to the second corner.