Development, application and validation of a new cooling technique applied for Inconel 718® machining

Abstract

Elevated temperatures can have detrimental effects on the quality of the machined output, including loss of dimensional tolerance, surface integrity issues and reduced tool life. Traditionally, the main method to avoid these problems is the application of Cutting Fluids in Abundance (CFA). However, this technique presents sustainability challenges in the social, environmental, and economic dimensions. Researchers have been exploring alternative cooling methods that aim to reduce or eliminate reliance on these inputs. This project sought to develop and test a new cooling method for machining, focusing on the turning of Inconel 718, a high-value superalloy. Coated tungsten carbide tools were used: TiNAl and a double coating, AlCrN over TiNAl, referred to as AlCrN+. They were integrated into an adapted tool holder with internal channels for circulation of a cooling fluid. An Design of Experiment (DoE) was employed, involving three atmospheres: internally cooled tools (ICTs), dry machining (DM) and the conventional use of abundant cutting fluids (CFA). Temperature analysis, conducted using a thermocamera and the tool-part thermocouple method, identified the speed (vc) and depth of cut (ap), as well as feed (f), atmospheres (ICT, DM and CFA), in addition to coatings (TiNAL and AlCrN+) as the main input variables that affect temperature. In this case, the TiNAl coating together with the ICTs contributed significantly to the temperature reduction. However, the temperature at the interface between the chip and the tool increased with the basic machining parameters (vc, ap, f) and was significantly affected by the atmosphere, with the ICTs demonstrating excellent performance. In terms of cutting forces, roughness and tool life, this research revealed that TiNAl together with ICTs outperformed CFA, removing 27% more material and an impressive 262% more than DM. AlCrN+ together with CFA, presented superior performance, providing a 46% increase in material removal compared to ICTs and a 306% increase in relation to DM. The TiNAl coating contributed to the increase in cutting forces, while other variables were not significant. Roughness was mainly influenced by coating, with no significant differences observed between atmospheres. Analyzes of wear mechanisms showed that abrasion, adhesion, oxidation and diffusion were observed regardless of coating or atmospheric conditions. Notably, the AlCrN+ coating showed a smoother and more uniform wear pattern, with a prevalence of flank and crater wear. In summary, internally cooled tools offer an innovative and environmentally friendly solution for machining operations. They excel in their heat dissipation capabilities, outperforming the CFA in some situations and significantly outperforming the DM. However, continuous efforts are needed to improve the lack of lubricity of the lubrication system and possible leakage problems.