Hole Quality and Multi-Objective Optimisation in Dry Drilling of GLARE 3-3/2 Fibre Metal Laminates with HSS and Carbide Drills

Drilling of fibre metal laminates is difficult because the metal and composite layers respond differently to machining. This study aimed to identify the drill and cutting parameters that give the best dry-drilled holes in GLARE (glass laminate aluminium reinforced epoxy) 3-3/2. Rolled and ground high-speed steel drills (HSS-R, HSS-G) and a carbide-tipped drill were tested in a 33 full factorial design (715–3030 rpm; 0.1–0.3 mm/rev), with measurements of thrust force, infrared temperature, entry and exit surface topography and hole-wall morphology. Drill type governed the thrust force and feed governed the drill temperature, while the workpiece temperature did not exceed 43.4 °C. Exit burrs were the main defect, and their character depended on drill-specific speed–feed combinations. The carbide-tipped drill gave the most accurate holes and the cleanest walls but the largest exit burrs; the HSS-R drill caused bell-mouthed entries and fibre pull-out. Multi-objective optimisation of the measured conditions with a weighted desirability function identified the HSS-G drill at 1520 rpm and 0.1–0.2 mm/rev as the best operating window (at 0.2 mm/rev: D = 0.867, peak thrust force 31.1 N, exit burr height 1.8 µm). Independent confirmation experiments are required before production use.