End Mill Having A Symmetric Index Angle Arrangement For Machining Titanium

An end mill for machining titanium, having a longitudinally extending rotation axis AR and comprising:

• a shank portion, and
• a cutting portion extending from the shank portion to a cutting end face and being integrally formed with at least four cutting teeth alternated with helically shaped flutes and having a cutting portion diameter DE;
• each tooth comprising
• a rake surface,
• a relief surface,
• a cutting edge formed at an intersection of the rake and relief surfaces, and
• a relief edge spaced apart from the cutting edge and formed at an intersection of the relief surface and an adjacent surface of the flute succeeding the tooth;
• each rake surface comprising
• a rake recessed sub-surface,
• a rake cutting sub-surface positioned further than the rake recessed sub-surface from the rotation axis and raised above the rake recessed sub-surface, relative to an imaginary radial line passing through the cutting edge, and
• a rake discontinuity formed at an intersection of the rake recessed and rake cutting sub-surfaces;
• wherein each tooth comprises an actual internal cutting angle formed at an intersection of the rake cutting sub-surface and the relief surface, the actual internal cutting angle having a greater value than an imaginary internal cutting angle formed at an intersection of imaginary extension lines of the rake recessed sub-surface and the relief surface;
• wherein each tooth has a rake cutting sub-surface length dimension LD, measured from the rake discontinuity thereof to the cutting edge thereof, fulfilling the condition 0.01RT<LD<0.05RT, wherein RT is the tooth's radius dimension, measured in a straight line from the rotation axis to the cutting edge;
• wherein each tooth has a radial rake angle within a range of 6° to −6°;
• wherein each flute has a helix angle H which fulfills the condition 30°<H<50°;
• wherein, in a plane perpendicular to the rotation axis AR, each flute comprises a convexly shaped ejecting portion and a concavely shaped bending portion connecting the ejecting portion and the rake recessed sub-surface;
• wherein the ejecting portion has an ejection height E which is measurable between an apex of the ejecting portion to an imaginary straight line extending from a nadir of the adjacent bending portion to the adjacent relief edge, the ejection height E having a magnitude fulfilling the condition 0.010DE<E<0.031DE;
• and
• wherein, at the cutting end face, index angles of the flutes are in a symmetric index angle arrangement.