Patent ID: 7335615

Claim:
A method of machining a workpiece comprising the steps of: providing a workpiece; providing a ceramic cutting insert formed from the consolidation of a starting powder mixture and having a rake surface and a flank surface wherein the rake surface and the flank surface intersect to form a cutting edge and the ceramic cutting insert having a substrate that comprises between about 15 volume percent and about 35 volume percent of a boron carbide phase and at least about 50 volume percent alumina, the substrate further contains the residue from one or more sintering aids present in the starting powder mixture in an amount between about 0.5 volume percent and about 5 volume percent of the starting powder mixture and being selected from the group comprising yttrium oxide, ytterbium oxide, yttrium aluminum garnet, lanthanum oxide, chromium oxide, and other rare earth oxides, and has a fracture toughness (K IC , 18.5 Kg Load E&C) greater than or equal to about 4.5 MPa·m 0.5 ; causing relative rotational movement between the workpiece and the ceramic cutting insert wherein the surface speed of the relative rotational movement is equal to or greater than about 457 surface meters per minute; and bringing the ceramic cutting insert and the workpiece into contact with each other so as to remove material from the workpiece.