Performance evaluation of PVD-coated twist drills in deep hole drilling of AISI 1045 steel: influence of cutting speed and drill point geometry

Abstract Deep hole drilling of AISI 1045 steel exhibits significant challenges due to excessive tool wear, poor hole quality, chip evacuation difficulties, and heat accumulation. Previous studies has been exclusively focused on uncoated conventional HSS drill bits and a critical research gap exists in evaluating the different drill point geometries and the effect of coatings. To fill the current gap, three different drill geometries involving 2-faceted, 4-faceted and 6-faceted were evaluated along with two PVD coatings namely, TiN and AlCrN at three levels of cutting speed i-e 15 m/min, 20 m/min and 25 m/min. A full factorial design was employed entailing 18-trials. This study aimed to systematically assess the effects of drill geometry, coating type, and cutting speed on key machinability indicators, including flank wear, surface roughness, diametric, cylindricity, and roundness errors. AlCrN coating outperformed the TiN coated counterpart due to its better thermal stability at elevated cutting temperatures. Maximum tool life of 42 holes was recorded with AlCrN coating at 25 m/min with 6-faceted tool geometric configuration, however with the same arrangement of cutting speed and tool geometry, tool life was dropped to approximately 24% with TiN coating. Tools having AlCrN coating showed 90% escalation in the value of tool life when cutting speed was increased from 15 m/min to 25 m/min. However, TiN coating produced 72% elevation in the said response with cutting speed increase from 15 m/min to 20 m/min while further increase to 25 m/min produced a corresponding reduction of 19%. All factors were statistically significant with cutting speed having its highest share of 53.29% PCR followed by tool geometry with ~ 19% PCR. The test in which maximum holes (42 holes) were drilled was recommended for deep hole drilling of AISI 1045 over TiN coating and the former is selected for further in-depth hole integrity evaluation including surface roughness, diametric, roundness and cylindricity errors. These findings provide valuable insights for optimizing drill selection in deep hole drilling applications, leading to improved tool longevity, machining precision, and overall process efficiency, particularly in industries manufacturing shafts, spindles, dies, and mold cooling channels.