Machinability study of coated and uncoated carbide tools in drilling inconel 718

Advanced materials such as aero-engine alloys, structural ceramics and hardened steels pose serious challenges for cutting tools material during machining. Nickel-base super alloys are generally known to be one of the most difficult materials to machine. Machining productivity can be significantly improved by employing the right combination of cutting tools, cutting conditions and machine tool without compromising the integrity and tolerance of the machined components. The objectives of this study are to evaluate the machining characteristics of new drill geometry and to established mathematical model of the responses when drilling Inconel 718 using various cutting conditions. Commercially available Inconel 718 was drilled using carbide cutting tool with various point angles at various cutting speed between 4.59 to 21.41 m/min and feed between 0.03 to 0.12 mm/rev in the wet condition and a constant depth of cut. The drills employed in this study were uncoated carbide, TiAlN coated carbide and AlTiN coated carbide with designated ISO grade K20/K30. The performance of the cutting tools in terms of tool life (T), surface roughness (Ra), cutting forces (Fz) and diameter error (DE) was described using factorial design and response surface methodology (RSM). Mathematical models of the drilling responses were developed using the proposed method. Results showed that the developed models were statistically valid and sound based on the experimental results within the acceptable range. The optimum cutting conditions were developed for all the responses with acceptable desirability. Dimensional accuracy and surface layer alteration of the drilled hole when using all type of cutting tools were compared traditionally between three different types of tool. Results showed that the accuracy varied for all chosen machining conditions and tool types but still within acceptable tolerance. Top surface layer and subsurface are significantly affected with ununiform layer and the presence of white layer. Highest microhardness at subsurface layer occured when using AlTiN coated carbide tool