On the existence of a thermal contact resistance at the tool-chip interface in dry cutting of AISI 1045: Formation mechanisms and influence on the cutting process

This paper questions the perfect thermal contact conditions usually assumed at the tool-chip interface in machining. Dry orthogonal cutting tests are first conducted on a AISI 1045 steel with TiN coated carbide tools. Tool-chip contact zones are analysed by SEM-EDS and sticking and sliding parts are dissociated. A formation mechanism of a Thermal Contact Resistance (TCR) is proposed from the real contact area extracted. A Finite Element (FE) model based on the Arbitrary-Lagrangian-Eulerian (ALE) approach is then employed to investigate the influence of such thermal contact conditions on the cutting process. Evolution of the main cutting outputs such as average cutting forces, average chip thickness, tool-chip contact length and thermal fields is assessed. It is demonstrated, on one side, that average cutting forces, chip thickness and tool-chip contact length are shown to be insensitive to a TCR. On the other side, heat flux transmitted to the tool, temperature distribution on the tool rake face as well as continuity of temperature across the tool-chip interface are clearly affected depending on its amplitude. This study emphasizes that the existence of a TCR at the tool-chip interface can completely modify local heat partition compared to a perfect thermal contact. The possible occurence of an imperfect contact in machining should be highly considered and modelled based on thermal exchange considerations. Local heat transfer models at the interface are still required to reach more reliable and physically based simulations.