Abstract
Inconel 718 is a superalloy, considered one of the least machinable materials. Tools must withstand a high level of temperatures and pressures in a very localized area, the abrasiveness of the hard carbides contained in the Inconel 718 microstructure and the adhesion tendency during its machining. Mechanical properties along with the low thermal conductivity become an important issue for the tool wear. The finishing operations for Inconel 718 are usually performed after solution heat treatment and age hardening of the material to give the superalloy a higher level of hardness. Carbide tools, cutting fluid (at normal or high pressures) and low cutting speed are the main recommendations for finish turning of Inconel 718. However, dry machining is preferable to the use of cutting fluids, because of its lower environmental impact and cost. Previous research has concluded that the elimination of cutting fluid in these processes is feasible when using hard carbide tools. Recent development of new PCBN (Polycrystalline Cubic Boron Nitride) grades for cutting tools with higher tenacity has allowed the application of these tool grades in the finishing operations of Inconel 718. This work studies the performance of commercial PCBN tools from four different tool manufacturers as well as an additional grade with equivalent performance during finish turning of Inconel 718 under dry conditions. Wear tests were carried out with different cutting conditions, determining the evolution of machining forces, surface roughness and tool wear. It is concluded that it is not industrially viable the high-speed finishing of Inconel 718 in a dry environment.
Highlights
In the context of heat-resistant alloys, there has been a noticeable upward trend over recent decades to employ nickel-based superalloys for manufacturing critical components under extreme service conditions
Recent development of new PCBN (Polycrystalline Cubic Boron Nitride) grades for cutting tools with higher tenacity has allowed the application of these tool grades in the finishing operations of Inconel 718
This work studies the performance of commercial PCBN tools from four different tool manufacturers as well as an additional grade with equivalent performance during finish turning of Inconel 718 under dry conditions
Summary
In the context of heat-resistant alloys, there has been a noticeable upward trend over recent decades to employ nickel-based superalloys for manufacturing critical components under extreme service conditions. Inconel 718 has become one of the most suitable candidates due to its unique properties at very high temperatures, such as high mechanical and thermal strength, formidable resistance to corrosion, and elevated creep resistance. It can be extensively found in gas turbines of jet engines or in steam turbines of nuclear plants (for example, blades, disks, bolts and valves) [1]. Its excellent mechanical and thermal properties at high temperature, coupled with a high work hardening tendency, poor thermal conductivity, chemical reactivity with tool materials, and the abrasive particles contained in its microstructure, produce notable wear of the cutting tool [2,3].
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