Experimental Investigation of Drilling Parameters Affecting Hole Quality in Glass Fiber/Polyester Composites

Glass fiber/polyester composites are increasingly used in naval, aerospace, and automotive industries due to their excellent strength-to-weight ratio and corrosion resistance. However, drilling-induced delamination remains a major concern that compromises hole quality and structural performance. In this study, the drilling behavior of randomly oriented chopped strand mat GFRP/polyester laminates (3 mm thickness, 5 layers, 450 g/m² areal density) was experimentally investigated under varying spindle speeds (1000–2000 RPM), feed rates (100–300 mm/min), and drill diameters (5, 8, and 10 mm). Hole quality was evaluated using AutoCAD-based measurement of the delamination factor. The results show that delamination factor increases with feed rate, while higher spindle speeds reduce it, in agreement with previous studies that attribute this behavior to reduced thrust forces. Among the tested conditions, the lowest delamination factor (≈1.09) was obtained at 1500 RPM and 100 mm/min feed rate, whereas the highest (≈1.54) occurred at 1000 RPM and 300 mm/min. The contribution of this work lies in focusing on the underexplored chopped strand mat GFRP/polyester composites and employing AutoCAD-based quantitative assessment, providing new insights and a practical baseline for improving drilling performance in these materials.