<p align="center">Abstract: Nickel-based (IN 718) superalloys are extensively used in the aerospace industry in the manufacturing of engine parts. The engine parts, especially the turbine blades are working at elevated temperatures, therefore are provided with thermal barrier coatings (TBC) to sustain a high-temperature&nbsp;air stream. In addition, cooling holes at different inclinations are needed on the blade surfaces. The purpose of the inclined holes is to minimize the usage of compressed air and also to avoid the turbulence of air for creating uniform film cooling.to reduce&nbsp;severe heat load&nbsp;and to improve their service life. The main challenges in drilling these holes in TBC on IN 718 are due to the complex physical and chemical properties of metal and ceramic layers. Therefore, researchers have used non-conventional machining processes, such as laser and electrical discharge machining. However, these processes time-consuming and have high initial cost. They also inflict surface damages on holes. To overcome these drawbacks conventional drilling has been adopted in this work. In conventional drilling, drilling thrust is an important parameter that helps understand the effect cutting parameters, drill geometry, and the quality of micro-hole surfaces. The major difficulties in conventional micro-hole drilling are rapid tool wear, chip clogging due to small flutes, restriction on coolant supply, lack of appropriate cutting parameter levels available for machining of multiple layers workpiece. Therefore, in this work, we analyze drilling thrust distribution over cutting edges for straight and inclined holes, under different cutting conditions. The input parameters considered here include: spindle speed, drill feed, and workpiece inclination, each at two levels. Each experiment was performed on TBC IN 718 sheet using a 600 μm TiAlN coated carbide drill under a dry peck drilling cycle. Each experiment was repeated twice. The results show that uncoated IN 718 shows a higher thrust force than the TB coated zirconia layer, whereas a straight drilled hole required a lower drilling thrust than the inclined hole. A higher elemental thrust is observed at the chisel edges than the main cutting edges in both, straight and inclined holes. Further, the thrust increases with an increase in the drill feed. In the case of inclined hole drilling, unequal elemental thrust is observed on each cutting edge. This is because drill cutting edge engagement with the workpiece varies with inclination angle. This elemental drilling thrust is varied non-linearly along the cutting edge direction.&nbsp; &nbsp;</p><p>Keywords: Inclined drilling, Drilling thrust, Drill engagement, TBC, IN718, Elemental thrust</p>

Analysis of Drilling Thrust for Straight and Inclined Micro-Holes in Thermal Barrier Coated Inconel 718 Superalloy

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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