Tool life and surface integrity aspects when drilling and hole making in Inconel 718

Drilling is one of the most important processes in aerospace manufacture and is often the last operation performed. When combined with the fact that holes amplify any in service stresses a significant demand for high surface integrity and production process security is created. In contrast to other machining processes there are relatively few publications regarding the drilling of nickel-based superalloys.Following a brief review on the general machinability of Inconel 718 a series of experiments examining the tool life/wear of various commercially available drills, recommended for use on nickel-based superalloys, is detailed. In addition a comparison of the resultant hole integrity produced by drilling alone is compared to that obtained using reaming and a relatively new technique of mill boring.The main conclusion is that when using commercially available drills the resulting hole quality is not sufficient to meet the requirements of the aerospace industry and therefore secondary processing is required. Mill boring with a standard milling tool appears to have significant potential for improving productivity and reducing costs compared to reaming.