Radius end mill and cutting method

A radius end mill comprising:

• an end mill body which is rotatable around an axis;
• peripheral cutting edges each formed at a peripheral portion of the end mill body located close to a distal end thereof so as to extend from the distal end of the end mill body toward a terminal end thereof;
• bottom cutting edges each formed at a distal end surface of the end mill body so as to extend from the vicinity of the axis outward in the radial direction of the end mill;
• and
• corner cutting edges each formed between the peripheral cutting edge and the bottom cutting edge so as to communicate the peripheral cutting edge with the bottom cutting edge, each of the corner cutting edges being formed so as to protrude outwardly in the radial direction of the end mill body and so as to protrude from the terminal end of the end mill body toward the distal end thereof;
• wherein:
• the corner cutting edge is formed so as to curve inward in the radial direction as the corner cutting edge approaches the distal end of the end mill body from the terminal end thereof and so as to curve toward the terminal end of the end mill body after the corner cutting edge has reached the distal end of the end mill body;
• the bottom cutting edge is formed so as to communicate with the corner cutting edge and so as to be close to the terminal end of the end mill body as the bottom cutting edge approaches inwardly in the radial direction;
• the value of a rake angle α of the corner cutting edge with respect to the axis is greater than or equal to −10° and is less than or equal to 10°;
• a rake surface of the corner cutting edge and a rake surface of the bottom cutting edge each are formed as a plane, and the rake surface of the corner cutting edge is formed so as to be flush with the rake surface of the bottom cutting edge;
• the corner cutting edge is formed so as to curve by a radius of curvature (R) around a center;
• the center of the radius of curvature (R) of the corner cutting edge is located closer to the distal end of the end mill body than a contact point (G) of the peripheral cutting edge and the corner cutting edge;
• and
• when an external diameter of the end mill body is (D), the value of the curvature radius R of the corner cutting edge is greater than or equal to 0.1×(D) and is less than or equal to 0.3×(D).