Drilling Machinability of Glass, Basalt, and Hybrid Epoxy Composites: Thrust Force, Thermal Load, and Hole Quality

The drilling machinability of glass fiber G₁₄, basalt fiber B₁₄, and two hybrid laminates (B₄G₆B₄, G₄B₆G₄) was evaluated through 36 full-factorial experiments employing an HSS-G drill, three spindle speeds (715, 1520, 3030 rpm), and three feed rates (0.1-0.3 mm rev^-1). Peak thrust force varied from 65.8 N for B14 at 0.1 mm rev^-1 to 174.3 N for G₁₄ at 0.3 mm rev^-1; hybrids occupied the intermediate range of 101-163 N. Infra-red thermography recorded maximum drill temperatures of 110-120 °C for G₁₄, almost double those of B₁₄, while both hybrids attenuated hotspots to below 90 °C. ANOVA attributed 73.4% of thrust force variance to feed rate, with material type and spindle speed contributing 15.5% and 1.7%, respectively; for temperature, material type governed 41.5% of variability versus 17.0% for speed. Dimensional quality tests revealed that the symmetric hybrid G₄B₆G₄ maintained entrance and exit diameters within ±2% of the nominal 6 mm, whereas B₄G₆B₄ over-expansion exceeded 8% at the lowest feed and G₁₄ exit diameters grew to 6.1 mm at 0.3 mm rev^-1. Integrating basalt compliance with glass stiffness, therefore, halves thrust force relative to G₁₄, suppresses delamination and overheating, and offers a practical strategy to prolong tool life and improve hole quality in multi-material composite structures. These insights guide parameter selection for lightweight hybrid composites in aerospace, renewable-energy installations, and marine components worldwide.