Assessing the torque and thrust forces in micro-drilling of thermal barrier coated nickel superalloys

Abstract

Nickel superalloys are crucial materials for aerospace applications, offering exceptional performance at high temperatures. Key components in aircraft engines, such as turbine blades, guiding vanes, afterburners, and casings, require the intricate process of micro-drilling to enable effusion cooling. However, when dealing with nickel-based superalloys, tool breakage during micro-drilling is a substantial drawback. This study investigates the cutting forces acting at the tool-workpiece interface during the micro-drilling of thermal barrier-coated Nimonic 90. The micro-drilling was conducted under three lubrication conditions: dry, flood, and 0.5% Graphene-based NMQL, utilizing a 700 μm diameter TiAlN-coated tungsten carbide drill. Experiments were performed at spindle speeds of 1000, 2000, and 3000 rpm, with a constant feed rate of 3 μm/rev. Results revealed that under dry conditions, the micro-drill failed after drilling just 16, 18, and 15 holes at spindle speeds of 1000, 2000, and 3000 rpm, respectively. In contrast, no failures occurred under flood and 0.5% Graphene-based NMQL lubrication conditions, likely due to improved heat dissipation, resulting in reduced thrust forces and torque acting on the micro-drill. Thrust force and torque values were measured using a Kistler 3-component mini dynamometer, with maximum values of 26 N and 0.31 N-m at 1000 rpm under dry lubrication conditions. These values decreased to 24 N and 0.25 N-m and 22 N and 0.19 N-m at spindle speeds of 2000 and 3000 rpm, respectively. NMQL lubrication conditions consistently exhibited lower thrust force and torque values compared to dry and flood conditions, with the lowest recorded values (12.5 N and 0.06 N-m) at 3000 rpm in the NMQL lubrication condition. The NMQL condition facilitated for efficient and better drilling operation due to the rolling effect produced by the graphene nanoparticles.