Effect of cooling scheme and coating of drills on hole quality in drilling of Inconel 718

Challenges in drilling nickel-based superalloys, such as Inconel 718 (IN718), are multifaceted. High requirement of hole surface quality in drilling such alloy must deal with extreme material properties and complex process condition in drilling operation. This paper presents an experimental investigation on the effect of PVD coated solid carbide drills under different internal cooling schemes on hole quality in drilling IN 718 alloy. Three types of solid carbide drills were used in the series of drilling experiments, including PVD coated and uncoated drills, and different design in the number of internal cooling channels, two channels and four channels. The objective of the investigation is to assess the effect of coating and efficiency of internal cooling on surface quality in drilling IN718 alloy. Surface quality on drilled holes in terms of roughness, burr formation, subsurface deformation and strain hardening has also been measured and analyzed on the machined specimen. The roughness and burr size on drilled holes demonstrated little differences among the three types of testing drills. Surface roughness was severely deteriorated by the chip trapped in the hole leaving scratch and smears on the surface. Nevertheless, the scheme of internal cooling channels and PVD coating exhibited noticeable influence on quality of drilled hole surface.