TOOL WEAR MECHANISM IN CONTINUOUS CUTTING OF HARDENED TOOL STEELS

Precision hard turning provides an alternative to grinding in some fin ishing applications. Rapid tool wear, however, remains an impediment t o the process being economically viable. This experimental study inves tigates microstructural aspects of cubic boron nitride (CBN) tool wear in finish hard turning. Results indicate the followig: (1) carbide si zes of the workpiece have significant effects on tool wear; (2) the fl ank wear rate can be correlated with mean carbide diameter of the work piece; (3) the wear resistance increases monotonically with decreasing CBN grain size: (4) in finish turning with low CBN content tools, the governing wear mechanism is fine scale attrition by microfracture and fatigue. A powder metallurgy M50 bar hard turned using an ultrafine C BN grain tool shows flank wear less than 45 mu m VBmax after 6.2 km cu tting distance; this wear rate equals 3.1 mu m/km, over an order of ma gnitude lower than when machining conventional M50 under identical con ditions. The surface finish is better than 80 nm R-a. (C) 1997 U.S. Go vernment. Published by Elsevier Science S.A.