Data-Driven Modeling of Thermal Regulation in CFRP Drilling: RSM-Based Combined Effects of Wax and Graphene Additives

Carbon fiber-reinforced polymer (CFRP) composites are increasingly used in lightweight structures; however, their poor thermal conductivity poses challenges during drilling, where excessive heat degrades the epoxy matrix. This study investigates the individual and combined effects of wax (0–2%) as a solid lubricant and graphene nanoplatelets (0–2%) as a heat dissipation enhancer on cutting temperature during CFRP drilling. A data-driven modeling approach based on response surface methodology (RSM) with dummy variables was developed using a full factorial design comprising 225 unique experimental conditions (9 formulations × 5 cutting speeds × 5 feed rates) with three replicates per condition, resulting in 675 individual drilling tests. The RSM model was fitted to the 225 condition means. The global RSM model achieved high predictive accuracy (R² = 0.9250, RMSE = 2.83 °C). Results show that increasing the feed rate reduces temperature by up to 29% and improves process stability, contrary to conventional metal cutting behavior. The addition of 2% wax reduced mean temperature by 11.3% and decreased thermal variability by 26%. Graphene exhibited an optimal concentration at 0.25%, yielding a 4.3% reduction in cutting temperature, with higher concentrations providing no additional benefit due to agglomeration. The combined effects of wax and graphene resulted in an optimal formulation containing 2% wax and 0.25% graphene, which provided the most favorable balance between low cutting temperature (46.1 °C) and enhanced thermal consistency (standard deviation = 3.53 °C). These findings provide practical guidelines for designing thermally regulated CFRP composites for high-performance drilling operations.