The effects of cutting conditions on cutting temperature and hole quality in drilling of inconel 718 using solid carbide drills

In this study, the drillability of Inconel 718, a nickel-based superalloy, which is frequently used in aerospace industry due to its superior mechanical and physical properties, was experimentally investigated under different cutting and cooling/lubrication conditions. Drilling tests were performed at 2 different cutting speeds (10, 15 m/min) and a constant feed (0.02 mm/rev) using TiAlN coated and uncoated solid carbide twist drills with diameter of 5 mm. The effects of cooling/lubricating conditions and coating material on drillability of Inconel 718 were evaluated in terms of the generated thrust force, torque, cutting temperature, hole quality (including surface roughness, hole diameter and roundness error, burr formation at the entrance and the exit of the hole, machined subsurface changes) and tool wear. Experimental results showed that different cooling/lubrication conditions have significant effects on all performance criteria. Cryogenic cooling significantly reduced the cutting temperatures. Generally, cryogenic drilling exhibited better performance on hole quality and surface integrity with less burr formation at the entrance and the exit of the hole, more accurate hole diameter, less roundness error, better machined subsurface quality, etc. However, it was determined that cryogenic conditions increased the thrust force and significantly reduced the tool life due to excessive chippings. Experiments under dry conditions did not show any superior performance to other conditions. Good surface roughness values and tool life were achieved in drilling test under wet conditions. The increased cutting speed improved the cutting performance, especially in cryogenic conditions. The use of the coating material (TiAlN) also reduced the tool wear dramatically.