Conceptual tribo-energetic analysis of cutting tool protective coating delamination in dry cutting of hard-to-cut aero engine alloys

Abstract

Machining in dry mode is characterized by intense thermo-mechanical loading. The coupling between the thermal and the mechanical loads may lead to tool failure, especially when machining the so-called hard-to-cut alloys. Within such environments the efficiency of heat removal plays an important role in preserving the structural integrity of the tool. Efficient heat removal in dry machining depends solely on the intrinsic thermal proper- ties of the tool for uncoated tools and on the effective properties of the tool-coating combinations for coated tools. Thermal loads may also accelerate wear of the tool. As such, a relationship between the wear and the intrinsic thermal properties of the tool is worthy of investigation. This paper investigates such a relationship. Here we team numerical simulations to SEM-imagery to map the thermal conductivity within the tool zone of action of a coated carbide tool. The results indicate that, depending on the temperature rise, the tool-tip might undergo a severe drop in thermal conduction. This drop may locally restrict the ability of the tool material to dissipate the applied thermal load. This may nucleate thermally congested clusters within the tool-tip where the material completely loses the ability to transport heat. Thermal congestion renders an energeti- cally active zone where the thermal energy available may be used to activate wear through different mechanisms. It is also found that the immediate layer under the surface of the tool tip is important to enhance the ability of the tool material to dissipate the thermal loads. The results also highlight the importance of matching the temperature dependant properties of the different coating layers in order to enhance delamination resistance.