Impact of feed rate, speed, and fiber orientation on drilling quality in coir epoxy composites

Coir fiber-reinforced epoxy composites are increasingly used in sustainable applications such as construction materials and furnishings. However, drilling these natural fiber composites poses challenges, including delamination, poor surface finish, and dimensional inaccuracies. This study evaluates the effects of feed rate, spindle speed, fiber orientation, and drill diameter on machining time, surface roughness, and hole circularity during drilling of coir-epoxy composites. Specimens were fabricated via hand lay-up with fibers oriented at 0, 45, and 0 + 90°, and characterized for tensile strength following ASTM standards. A Taguchi L27 orthogonal array was employed to design experiments, with analysis of variance (ANOVA) used to quantify parameter significance. Results indicate that spindle speed significantly influences machining time and surface roughness, while drill diameter and fiber orientation primarily affect hole circularity. Notably, the 0 + 90° orientation demonstrated the highest tensile modulus (1.011 GPa). Optimized drilling conditions for minimal machining time included 0° orientation, 0.125 mm/rev feed rate, 1160 rpm spindle speed, and 6 mm drill diameter. Superior surface finish was achieved at 0° orientation, 1.25 mm/rev feed, and 580 rpm speed, whereas optimal circularity required 0/90° orientation and an 8 mm drill. These findings provide new insights into the machining behavior of coir-reinforced composites and establish parameter guidelines to enhance drilling performance and dimensional accuracy in sustainable composite manufacturing.