Investigation of hole drilling operations in cryogenic treated Inconel 718 alloys

In this study, the drilling operations of cryogenically treated and untreated Inconel 718 workpieces were experimentally investigated at different cutting parameters. For this purpose, one of the Inconel 718 work-piece was applied deep cryogenic treatment at -146 °C for 24 hours and tempering process twice (2 hours at 200 °C). Drilling tests were performed in dry cutting conditions with TiSiN coated carbide drills with a diameter of 10 mm, 4 different cutting speeds (10, 13, 16, 19 m/min), and 3 different feeds (0,06, 0,09, 0,12 mm) at 8 mm constant cutting depth parameters. Tool life tests were conducted with 8 mm depth of cut, 10 m/min cutting speed and 0.06 mm/rev feed. In the experiments, cutting forces, surface roughness, tool wear, tool life, micro-hardness and microstructure were examined to see the effect of cutting parameters and cryogenic treatment on drilling of Inconel 718 work-piece. The cryogenic treatment resulted in an increase in the micro-hardness of the Inconel 718 alloy, a reduction in grain sizes, precipitation of more y" phases, and thinning and homogeneous distribution of the carbides. In addition, it caused the feed forces to increase and the surface roughness values to decrease in hole drilling operations. In the tool life experiments, it was observed that the cutting tool used in cryogenically treated Inconel 718 alloy was worn less and the tool life increased. In the hole drilling experiments, the increase in the cutting force caused the cutting forces to increase, and the increase in the cutting speed caused the feed forces to increase first and then decrease. In addition, it was observed that the surface roughness increased with increase in feed and decreased first with increasing cutting speed and then increased. In tool life experiments, higher feed forces were obtained when the cryogenically treated workpiece was drilled, compared to the untreated work-piece, while lower values were obtained in cryogenically treated work-pieces than the untreated work-piece in terms of surface roughness.