Effects of cooling strategies and tool coatings on cutting forces and tooth frequency in high-speed down-milling of Inconel-718 using helical bull-nose solid carbide end mills

This paper presents the results of experimental investigation of the effects of three cooling strategies (minimum quantity lubrication (MQL), cryogenic cooling using liquid nitrogen (LN2), and combined (MQL + LN2)) and three tool coatings (uncoated and AlTiN- and GMS(2)-coated) on cutting force components (F (x) , F (y) , F (z) ); the resultant cutting force, F (r) ; and cutter tooth frequency in peripheral high--speed end milling of Inconel-718 to improve machinability and reduce cost. All the experiments were conducted on a Cincinnati Milacron Sabre 750 vertical machining center (VMC), equipped with Acramatic 2100 CNC controller using uncoated and AlTiN- and GMS(2)-coated solid carbide bull-nose helical end mills of 12.7 mm (0.5 in.) diameter, and 0.762 mm (0.03 in.) corner radius. Each experiment consisted of eight passes, each pass of 76.2 mm (3 in.) cutting length. Axial and radial depths of cut, cutting speed, and material removal rate were kept constant for all experiments. The experimental results show that uncoated end mills generated lowest resultant cutting forces, whereas GMS(2)-coated end mills generated highest resultant cutting forces under all cooling strategies. MQL cooling strategy generated lowest resultant cutting forces, whereas LN2 cooling strategy generated highest resultant cutting forces for all end mill coatings. Using LN2 cooling strategy alone is not recommended for machining Inconel-718 due to high cutting forces and vibrations. Uncoated end mills under MQL cooling strategy generated the lowest cutting forces and are recommended for machining Inconel-718, whereas GMS(2)-coated end mills under LN2 cooling strategy generated highest cutting forces.