Hard turning of tempered DIN 100Cr6 steel with coated and no coated CBN inserts

Recent improvements in the machine tools technology (specially the stiffness and positioning accuracy) as well as the advent of the cubic boron nitride (CBN) ceramic cutting tools made the finishing operations for machining hardened steel parts possible, using tools with defined cutting geometry in substitution to the traditional grinding operations. The advantages presented by the hard turning are sufficiently attractive for many plants, however these are still reluctant to adopt and substitute a well known and dominated process (grinding) for other one not totally understood. Aiming to expand the knowledge of the processing effects of hard turning on the finishing of the machined workpiece, as well as the effects on the tool wear life. Series of experiments with seven different types of CBN inserts had been carried out using inserts with wiper geometry, coated with TiAIN and TiN as well as with no coated ones. The cutting parameters had been specified in such a form to cover the entire field recommended by tool suppliers. The machined part was an axle of DIN 100Cr6 steel tempered to 62 HRc. All the machining operations were carried out at a Mazak-Quick-Turn using an tool holder DCLNR-164D with insert geometry ISO CNGA120408SO1020 with edge with T preparation with 0.102 mm, x 20 degrees. The tool wear control was carried out using an optic microscope Zollern Saturn and a roughness profiler Hommelwerk T8000. Following parameters were parameters were determined: VBMAX, R-a, material removal rate and the tool life determined by the Taylor's equation obtained for theoretically ideal cutting conditions. Preliminary analyses of the results compares with the literature indicating that they are significant. (c) 2006 Elsevier B.V. All rights reserved.