Some effects of cutting edge preparation and geometric modifications when turning INCONEL 718™ at high cutting speeds

The geometry of the cutting edge and its preparation can play a significant role on the insert performance, directly affecting tool life, surface finish and surface integrity. This paper evaluates the performance of some inserts subjected to modifications on the edge geometric form and preparation, when turning, at high cutting speed, a nickel-based alloy, INCONEL 718(TM), hardened by solution and precipitation (44 HRc). The modifications were applied to different tool materials (Al2O3-based, Al2O3-based + SiCW and PCBN), in an attempt to improve tool performance when turning this difficult-to-machine alloy at high speed. The evaluation addressed tool wear, surface roughness and temperature at 1.5 mm away from the cutting edge, turning with finishing cutting conditions (500 m/min, cutting speed, 0.1 mm/rev feed rate and 0.35 mm depth of cut). The results show that some modifications caused significant improvements on the insert performance for all the tool materials tested. When using the best modification, tool wear, temperature and surface roughness are lower, residual stress were highly compressive while subsurface hardness did not show any significant modification. Microstructure alterations were also not observed in any surface produced at the cutting condition investigated. (C) 2004 Elsevier B.V. All rights reserved.