Influence of various tool coatings and cutting parameters on the drilling performance of CGI500

The replacement of Flake Graphite Iron (FGI) with Compacted Graphite Iron (CGI) in the production of internal combustion engine blocks has led to significant improvements in engine performance. However, CGI exhibits lower machinability, posing a considerable challenge to the machining industry. This study investigates the effects of different tool coatings (Fire, Endurum, and Signum) on tool life, process temperature, and wear mechanisms during the drilling of CGI500. A Design of Experiments (DoE) approach was employed, and results were analyzed using Analysis of Variance (ANOVA). ANOVA revealed that coating type was the only statistically significant factor (p = 0.043) affecting the number of holes drilled at 100 μm flank wear, whereas cutting speed and feed rate were not significant at this threshold. The Signum coating exhibited the lowest wear rate per hole (best case: 0.26 μm/hole under Condition 2), attributed to its higher nanohardness (3546 HV vs. 2964 HV for Fire), superior adhesion (critical scratch load: 88 N vs. 73 N), and greater thickness. However, when tool life was normalized by coating thickness, Fire outperformed the other coatings in most conditions, suggesting that thickness is a dominant factor in Signum’s raw performance advantage. Temperature measurements via embedded T-type thermocouples showed that cutting speed was the only significant factor (p = 0.046) for new drills, while at advanced wear states all factors (Vc, fz, coating) became significant (p < 0.01). Post-test SEM-EDS analysis after chemical etching confirmed that attrition was the dominant wear mechanism under all conditions, and coatings affected wear rate but not wear mechanism.