Thermal behavior analysis of coated cutting tool using analytical solutions

Abstract

Nowadays, almost all cutting tools are coated due to improvements in manufacturing processes. The two main reasons are: (1) coatings allow a cut with less friction and less wear resulting in longer tool life and (2) thermal barrier effect, since the contact between workpiece–tool–chip occurs in the coating and not in the tool material (substrate). This paper analyzes, the thermal effect of the coating without considering the tribological effect. The thermal behavior with three types of coating: cobalt (Co), titanium nitride (TiN), and aluminum oxide ($\hbox {Al}_2 \hbox {O}_3$) on a ISO K10 carbide insert of 3 mm thickness was investigated. This paper investigates the behavior of inserts with coatings of thickness of 1, 2, 5, 10, and $20\,\upmu$m in a one-dimensional transient thermal model proposed for a material composed of two layers. A constant heat flux simulates the heat generated in the tool–piece–chip interface for coated and non-coated inserts. The solution of the diffusion equation is obtained using the Green function method. The effect of the coating can then be calculated by analyzing the evolution of the temperature at the cutting interface in contact with the heat flux and the evolution of the temperature at the coating–substrate interface. It can be concluded that coatings have thermal barrier effect, although for coatings of $2\,\upmu$m thickness, this influence is very small and produces temperature reduction of up to 14%. For thicknesses greater than $5 \upmu$m, the effect becomes considerable depending on the coating–substrate pair. In the case of TiN carbide, the temperature reduction is 26, 34, and 41% for the thicknesses of 5, 10, and $20\, \upmu$m, respectively.