Temperature and wear of cutting tools in high-speed machining of Inconel 718 and Ti-6Al-6V-2Sn

The present paper deals with the high-speed machining of Inconel 718 and Ti-6Al-6V-2Sn alloys from a thermal point of view. Temperature and wear of cutting tools are investigated by means of cutting experiments and numerical analysis up to a cutting speed of around 600 m min(-1). For Inconel 718, severe wear of ceramic tools, particularly highly developed boundary notch wear, is correlated with variation of the chip formation mechanism from continuous to discontinuous, which is accompanied by large side Bow of the chip and plastic burrs of the workpiece. This indicates that the wear is developed by an abrasive process rather than by a thermally activated mechanism. A TiC-added alumina tool is superior to silicon nitride across a speed range from 250 to 500 m min(-1), where the cutting temperature exceeds 1200 degrees C. In end milling of the titanium alloy, high-speed machining up to a cutting speed of 628 m min(-1) (20 000 r.p.m.) is possible for sintered carbide tools. Measurements of cutting temperatures during intermittent turning of a titanium disk, which is modelled on milling, reveal that the feasibility of high-speed end milling depends on a transient temperature rise or 'time-lag', owing to a short cut distance of the tool edge per single revolution, the existence of the helix angle, and a temperature drop through the use of a coolant. These factors contribute to the reduction of tool temperature. Finally, a numerical model is proposed to validate the temperature measurement. (C) 1997 Elsevier Science S.A.