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

A cutting insert, comprising:

• an upper surface;
• a lower surface;
• a side surface which is connected to the upper surface and the lower surface, and comprises a first side surface and a second side surface;
• and
• a cutting edge comprises a first flat cutting edge and a first major cutting edge in an intersection region of the first side surface and the upper surface, and a second flat cutting edge, and a second major cutting edge in an intersection region of the second side surface and the upper surface,
• wherein the first side surface comprises a first curved side surface, a first corner side surface, and a first major side surface, the second side surface comprises a second curved side surface, a second corner side surface, and a second major side surface,
• the intersection region of the second side surface and the upper surface comprises a first intersection region of the second curved side surface and the upper surface, and a second intersection region of the second corner side surface and the upper surface, and
• the first intersection region has a downward convex curve with respect to a reference plane perpendicular to a central axis of the cutting insert in a side view and wherein the downward convex curve provides a lowermost portion in the first intersection region in a side view,
• and the second intersection region comprises a first inclined cutting edge that is inclined upward with respect to the reference plane in a direction away from the downward convex curve in the side view.

A cutting insert, comprising:

• an upper surface;
• a lower surface;
• a side surface which is connected to the upper surface and the lower surface, and comprises a first side surface and a second side surface;
• and
• a cutting edge comprises a first flat cutting edge and a first major cutting edge in an intersection region of the first side surface and the upper surface, and a second flat cutting edge, and a second major cutting edge in an intersection region of the second side surface and the upper surface,
• wherein the first side surface comprises a first corner side surface, and a first major side surface, the second side surface comprises a second corner side surface, and a second major side surface,
• the intersection region of the second side surface and the upper surface comprises a first intersection region and a second intersection region, and
• the first intersection region has a downward convex curve with respect to a reference plane perpendicular to a central axis of the cutting insert in a side view and wherein the downward convex curve provides a lowermost portion in the first intersection region in a side view,
• and the second intersection region comprises a first inclined cutting edge that is inclined upward with respect to the reference plane in a direction away from the downward convex curve in the side view.