Micro-drilling of straight and inclined holes on thermal barrier coated Inconel 718 for turbine blade cooling
Avinash N. Khadtare, Raju Pawade, Alwin Varghese, Suhas S. Joshi
Abstract
Thermal barrier coatings (TBC) are widely used on turbine blades working at high-temperature condition. Drilling different angled cooling holes on these blades is essential to minimize the severe heat load experienced and to improve their service life. In this study, mechanical micro-drilling is proposed to check the feasibility of the process and study the basic characteristics of thrust signal. The drilling experiments were performed on TBC Inconel 718 to drill micro-holes at different inclinations using 600-μm TiAlN-coated carbide drill under dry environment. Drilling performance is assessed in terms of the number of holes produced before drill breakage, drilling thrust, fluctuation of thrust signal, and tool wear. The longest tool life was observed while drilling at the combination of lower spindle speed and drill feed for both straight and inclined holes. However, the life of drill while drilling inclined holes was found to be lesser than that of the straight holes and spindle speed is found to be a statistically significant parameter affecting the drilling thrust. Two different drill wear mechanisms, namely, abrasion and adhesion were observed during drilling. Finally, during the drill failure phase, a large fluctuation in thrust signal was observed followed by the drill breakage.