Manufacturing Technology 2019, 19(2):254-260 | DOI: 10.21062/ujep/279.2019/a/1213-2489/MT/19/2/254

The Change of Tool Life in a Wide Range of Cutting Speeds in Hard Turning

János Kundrák, Zoltán Pálmai

Institute of Manufacturing Science, University of Miskolc, Miskolc-Egyetemváros, Hungary

Tool life changes according to a curve presenting two extreme values depending on the cutting speed. Besides the well-known Taylor formula, several other functions describe tool life, mainly for the 3rd speed range beginning with a tool-life maximum. In earlier studies the authors suggested a tool-life function valid for the whole speed range. Here the machinability of hardened steel is being investigated in a wide range of cutting speeds. The intention of this study is to work out a method for the physical interpretation of tool degradation defining the tool life. For this purpose the nonlinear differential equation of wear rate is applied. During the experimental work the tool life was measured when boring a 100Cr6 hardened workpiece of 75 mm diameterin the speed range vc=10…120 m/min with a feed rate of f=0.075 mm/rev, depth of cut ap=0.1 mm, γr=-5° and the life criterion Wcr=0.4 mm. The results proved the supposition that at a speed smaller than the tool-life maximum it is abrasion and adhesion that causes the tool deterioration, while above this speed, the thermo-activated degradation process plays an increasingly large role as speed increases. Calculating from the results of the cutting examination, the activating energy of the degradation process is Q=136±29 KJ/mol, on the basis of which it is likely that the degradation of the tool material occurs through the recrystallization of the surface layer from cubic into hexagonal, causing the surface layer to wear out more rapidly.

Keywords: Hard turning, PCBN tool, Tool-life function, Wear equation

Grants and funding:

Project no. NKFI-125117, National Research, Development and Innovation Fund of Hungary, financed under the K_17 funding scheme.
EFOP-3.6.1-16-00011 “Younger and Renewing University – Innovative Knowledge City – institutional development of the University of Miskolc aiming at intelligent specialization” project implemented in the framework of the Szechenyi 2020 program. The realization of this project is supported by the European Union, co-financed by the European Social Fund.

Published: April 1, 2019  Show citation