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Inconel 625 and Inconel 718 are nickel-based alloys which are heat and corrosion resistant, as such they are used in aerospace, petrochemical, nuclear and biomedical applications. Numerous previous studies have been conducted regarding the machinability of Inconel 718, but very little machinability data is available for Inconel 625. The aim of the study presented was to investigate the machinability of Inconel 625 and the more commonly-used Inconel 718, when cut with coated carbide tools. Inconel 625 was tested in its annealed form, whilst Inconel 718 was tested in a solution treated and aged condition. Tests were carried out for a turning process. The main focus of the study was on tool life and cutting forces, however some interesting insights are provided regarding chip formation and machining dynamics (vibration) issues.
Orthogonal cutting force measurements showed that for Inconel 718 there was a linear relationship between the feed rate (chip thickness) and cutting forces, whereas Inconel 625 showed a non-linear relationship in the feed range studied. This non-linearity was reflected by dynamic behavior documented when roughing Inconel 625 using RCMT round inserts, with vibration being observed only at certain feed rates.
VNMG rhombic, CNMG rhombic and RCMT round carbide inserts were tested for their performance in cutting Inconel 718. 15 minutes of tool life could not be achieved when machining Inconel 718 with VNMG inserts. Burring, depth of cut notch wear and tool edge fracture were key factors. CNMG inserts were more successful. The material removal rate achieved, and the total material removed per RCMT round insert, was 4 to 5 times the value achieved using the CNMG rhombic inserts, which shows the promise of round “button” inserts for roughing operations.