Tool wear/life evaluation when finish turning Inconel 718 using PCBN tooling

Following a brief review of related literature, the paper outlines experimental results following finish turning of Inconel 718 using low concentration PCBN inserts. Testing utilised a modified L36 Taguchi fractional factorial orthogonal array which evaluated the effects of tool insert shape/geometry (round, C-type), tool edge preparation (extra honed, chamfered & honed), fluid pressure (10, 100 bar), tool coating (uncoated, TiAlN+TiN), cutting speed (150, 300, 450m/min) and feed rate (0.05, 0.10, 0.20 mm/rev) at a constant depth of cut of 0.2 mm. At the lowest cutting speed (150m/min), average tool life using the round insert was approximately 5 times longer in comparison to the C-type tool, with severe grooving and built up edge (BUE) formation observed on wear scar micrographs in all experiments with the latter. As cutting speed was increased to 300m/min, the presence of grooving and BUE diminished, leading to comparable performance between the C-type and round tools. When turning at 450m/min however, several instances of catastrophic insert fracture occurred and tool life did not exceed 3.5mins, irrespective of the other parameters/conditions used. Adhesion of workpiece material on tool cutting edges was prevalent over the range of parameters tested with abrasion typically the primary mechanism causing insert wear.