ANOVA- Based Delamination and Microstructural Analysis of Drilled Glass/Basalt Composites

Polymer fiber composites such as glass fiber-reinforced polymer (GFRP) and basalt fiber-reinforced polymer (BFRP) exhibit superior strength-to-weight ratios (>5:1) and thermal resistance (>200 °C), making them integral to high-friction mechanical assemblies, insulating panels, fiberboards, and automotive interiors. These materials frequently require precision secondary machining, with drilling being the primary operation for assembly. This study quantitatively evaluates the drilling performance of bi-directional GFRP and BFRP composites using an experimental–analytical approach. A Taguchi L27 orthogonal array design was implemented to systematically vary feed rate (0.05–0.25 mm/rev), spindle speed (1000–3000 rpm), and drill point angle (90°–135°), assessing their influence on thrust force (60–300 N), delamination factor (1.00–1.45), and microstructural integrity. ANOVA results showed that 4 of 6 process parameters had a statistically significant effect on delamination (p < 0.05), explaining 92.06% of its variance (R² = 0.9206). Drill point angle (p = 0.077) and drill tool material (p = 0.742) did not show significance at the 5% level. Multiple linear regression (MLR) equations were derived to quantify parameter–response relationships, yielding prediction errors below 8%. Signal-to-noise (S/N) ratio analysis within the Taguchi framework identified the optimal drilling configuration as 2000 rpm spindle speed, 0.10 mm/rev feed rate, and 118° drill point angle, reducing delamination by up to 15% compared to non-optimized conditions. The findings demonstrate that parameter optimization can substantially minimize drilling-induced damage, improve hole dimensional accuracy by ±0.05 mm, and enhance the structural integrity of fiber- reinforced composites for high-performance applications.