Contact temperature and forces in the cutting of austenitic steel

Abstract

115 Along with the cutting temperature, the character of the contact interaction largely determines the war rate of a hardalloy tool in cutting steel. Therefore, research in this area provides the theoretical basis for the development of practical measures to reduce wear. (For austenitic steel and other hard materials, this is especially important at the rear tool surface.) Previous research has focused on the contact in the cutting of austenitic steel (1); the frictional coefficient in the wear area (2); and the temperature at the tool's contact surfaces (3). In the present work, we analyze those results (together with additional experimental data) so as to obtain more reliable conclusions regarding the contact interaction. The frictional coefficients μ fr and μ re at the front surface and rear wear area, respectively, are calculated on the basis of experimental values of the normal Pγn and tangential Pγτ forces at the front surface. To this end, we extrapolate the vertical Pz and horizontal Pxy components of the cutting force to zero rear wear area. (In the subsequent calculations, the forces Pγn = Pz0 and Pγτ = Pxy0 at the front surface are assumed con� stant.) Then, after measuring Pz and Pxy with different width hre of the rear wear area, we determine the nor� mal P hn and tangential P hτ forces at the rear wear area (4) Phn = Pxy - Pxy0, Phτ = Pz - Pz0. The same data regarding the forces at the contact surfaces are used to calculate the temperatures θfr at the front surface and θre at the rear wear area on the basis of the method in (5); the temperature dependence of the steel's ther� mophysical parameters is taken into account here by means of an iterativeapproximation algorithm (3). The calculated temperature θfr at the front surface is practically independent of the width hre of the rear wear area. The initial experimental data are obtained in turn� ing 12X18H10T steel by VK6 and TT20K9 hardalloy tools: supply 0.3 mm/turn; cutting depth 1.5 mm; cut� ter parameters γ = 0°, α = 10°, ϕ = 45°. The cutting speed v is assumed to be such as to eliminate dead zones at the front surface and also intense crater for� mation: v = 45-90 m/min for VK6 alloy and v = 30- 120 m/min for TT20K9 alloy. The cuttingforce com� ponents Pz, Py, and Px are measured by a UDM�600 dynamometer with a TA�5 tension system. The