Thermophysical-Property-Based Selection of Tool Protective Coatings for Dry Machining of Steels

A method is proposed for determining the optimum cutting conditions in dry turning of carbon and stainless steels using multilayer coated tools for physical criteria such as the maximum temperature of a cutting tool or maximum heat flux. The modified thermal number describing the tool-chip behavior, is introduced. The correlation between the thermal number and the average tool-chip interface temperature and frictional heat flux is examined for both flat-faced and grooved rake configurations. Although not shown here directly, the thermal barrier effect observed for multilayer coatings with an intermediate $Al2O3$ layer increases the heat partition to the chip at substantially reduced cutting temperatures. The experimental results indicate that thermal and tribological outputs from the interface are sensitive to changes in the thermophysical properties of the workpiece and coating materials, in particular the thermal conductivity, thermal diffusivity and the heat transmission coefficient. It was proven that the described approach makes it possible to select the appropriate cutting conditions based on process constraints such as the heat transfer intensity and temperature on the tool face.