Wear performance and mechanisms of PCBN tools in boring of powder metallurgy steels

Abstract

Wear performance and mechanisms of PCBN tools with different CBN content (80% vol. and 95% vol.) and cutting edge geometry (honed edge radius, 0.05 mm chamfered edge width, and 0.10 mm chamfered edge width) in boring powder metallurgy (PM) steels had been evaluated. Post-cutting examination of the worn cutting inserts was performed using focus variation microscopy (FVM), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The advanced three-dimensional wear characterization parameters WRM, WMD, WAM, WMH, and WAA are used to measure the wear of PCBN tools. A novel characterization method of removed material (η1 = WMD/WRM) and adhered material (η2 = WMH/WAM) was used to measure the trend of tool wear in this paper. With the increasing of CBN content, the PCBN tool wear parameters WRM, WMD, and WAA were decreased; adhesion was increased by WAM and WMH parameter characterization. For the variation of cutting edge geometry, chamfered edge showed a higher tool life and better wear performance than honed edge radius. With the increasing of chamfered edge width from 0.05 to 0.10 mm, the three-dimensional wear WRM, WMD, WAM, and WMH were increased. WAA showed an opposite trend and parameters η1 and η2 showed a not convergence trend. Besides typical wear mechanisms such as diffusion, adhesion, abrasive, microchipping was observed on PCBN tool; the tool protection layer (TPL) formation and peeling and impact load could be the reasons to explain the microchipping that occurred on cutting edge. Tool life is measured by surface roughness and calculated according to the number of workpieces processed. The results showed that PCBN tool with 95% vol. CBN content and 0.10 mm chamfered edge width achieves higher tool life.