An assessment of tool life in drilling of Inconel 718 using cathodic arc PVD coated carbide bits

The study investigates the performance of TiN and TiAlN coated carbide tools to improve the tool life in the limited explored drilling operation of difficult-to-cut Inconel 718 (IN 718). We deposited these coatings over tungsten carbide (WC) drill bits through the cathodic arc PVD route and evaluated their tool life at optimized machining parameters. Tool wear initiated with chipping at the corner of the margin and cutting edge (periphery wear), followed by coating abrasion and flank wear. In the case of TiAlN coated drill bit, we observed a notable built-up edge (BUE), indicating adhesive wear, which is not distinctly noticeable in the case of TiN coated drill bits. The comparison of the associated machining challenges between IN 718 and relatively softer EN 24 revealed no chipping but a significant built-up edge in the case of EN 24. At optimized machining parameters of 800 rpm spindle speed and 30 mm/min feed rate, TiAlN and TiN coated drill bits performed 2 and 1.6 times, respectively, better than uncoated drill bits in terms of the number of holes drilled. In addition, the performance of commercially available TiAlN coated drill bits was also compared with that of TiAlN coated drill bits produced in the present study by employing identical machining conditions. The in-house TiAlN coated drill bits yielded 50% additional life than the commercially available TiAlN coated drill bits. Additionally, the machined surface of drilled holes with TiAlN coated drill bits resulted in lower roughness (Ra) than the uncoated drill bits at the end of the respective tool life. The underlying reasons were analyzed and discussed.