Wear Analysis and Tool Life Modeling in Micro Drilling of Inconel 718 Superalloy

Aircraft engine parts, specifically blades, discs, and sheets are primarily made up of Inconel 718, which required drilled holes for assembly. Drilling holes in Inconel 718 is very difficult due to its high hardness, especially microdrilling. The primary studies majorly used uncoated drills for microdrilling Inconel 718, which leads to low tool life due to frequent tool wear. Microdrills bearing different coatings have not been investigated for their efficiency and mechanism of wear in microdrilling of super alloys. Also, time-dependent prediction of cutting tool wear has not been addressed adequately. In this study, a theoretical model to predict tool wear in drilling as a function of time and to evaluate tool life of anti-abrasion-, TiAlSiN-, and TiAlN-coated drills are presented. Considering feed rate and cutting speed as independent variables microdrilling experiments were conducted. In addition, the model estimates the progression of abrasion wear in various sections of the drill and the section with highest wear-rate was considered for calculation of drill life. Life of uncoated and coated drills were also calculated using a failure criterion of 31.3 mu m and Taylor's tool life exponents. Finally, a comparison of the experimental and modelling results was done to validate the model. It was observed that the model and experimental results are in good agreement at low and medium cutting speed. Both the coatings increased the life of the drills compared to uncoated drills. The wear-rate is highest at the corner of the drill. The mode of failure for TiAlSiN-coated drill was noticed to be corner chipping and for TiAlN-coated tool was built-up-edge (BUE) formation followed by flank chipping.