Cutting insert and processing method

A cutting insert having a surface involved in cutting, the surface being composed of a cBN-based sintered material, a diamond-based sintered material, a ceramic, a cermet, or a cemented carbide,

• the cutting insert comprising:
• a rake face;
• a flank face;
• and a cutting edge constituted of a ridgeline between the rake face and the flank face, wherein
• the cutting edge has
• a first cutting edge portion for corner processing,
• a second cutting edge portion for low cut-in pulling processing,
• a third cutting edge portion for high cut-in pulling processing,
• a fourth cutting edge portion for finished-surface processing,
• a first connection cutting edge portion that connects the first cutting edge portion and the fourth cutting edge portion,
• a second connection cutting edge portion that connects the second cutting edge portion and the fourth cutting edge portion, and
• a third connection cutting edge portion that connects the second cutting edge portion and the third cutting edge portion,
• the fourth cutting edge portion is disposed between the first cutting edge portion and the second cutting edge portion,
• the second cutting edge portion is disposed between the fourth cutting edge portion and the third cutting edge portion,
• each of the first cutting edge portion, the second cutting edge portion, and the fourth cutting edge portion has a curved shape,
• a curvature radius of the first cutting edge portion is 0.1 mm or more and 2.4 mm or less,
• a curvature radius of the second cutting edge portion is 3 mm or more,
• a curvature radius of the fourth cutting edge portion is 3 mm or more,
• the third cutting edge portion has a straight line shape, and
• each of the first connection cutting edge portion, the second connection cutting edge portion, and the third connection cutting edge portion has a curved shape,
• a curvature radius of the second cutting edge portion is smaller than a curvature radius of the fourth cutting edge portion.