Experimental Study in Micro-drilling Mechanism on Heterogeneous Structure of Thermal Barrier Coated Inconel 718 Superalloy

Abstract

Thermal barrier coated (TBC) superalloys are extensively used for manufacturing turbine blades to sustain high temperature zone while in operation. The production of cooling holes on these blades surface at various inclinations to the surface is essential to minimize the severe heat load experienced during working to achieve higher service life. Manufacturing of these holes is a main challenge in TBC superalloys due to combined metal and ceramic layers along the hole depth which effect on the thrust force generation, tool life and hole quality. Therefore, in this study mechanical micro-drilling is proposed to analyze the above highlighted difficulty. The experiments were performed on TBC Inconel 718 sheet having 3.3 mm thickness using 600 μm TiAlN coated carbide drill under dry environment. Three input parameters with their two levels are chosen for experimentations and each experiment is performed two times. Micro-drilling performance is assessed in terms of drilling thrust at different material layer with hole depth, taper of hole and distribution of thrust along the cutting edge of drill. Results show that magnitude of dynamic drilling thrust variation is observed at interface drilling irrespective of hole orientation. Whereas, maximum drilling thrust is observed before retraction of the drill. Magnitude of thrust force and fluctuation of thrust signal increases with depth of hole due to chip clogging in flute space. Minimum taper of a hole is observed in case of straight hole drilling than inclined hole whereas circular shape of hole is produced in straight hole drilling whereas elliptical hole is produced in case of inclined hole. Equal amount of thrust distribution along the cutting edge is observed in case of straight hole drilling but unequal amount of thrust distribution is seen in of case inclined hole due to drill-workpiece interaction. © 2023, The Author(s), under exclusive licence to Korean Society for Precision Engineering.