Optimizing drilling parameters for fly ash-filled hemp/epoxy composites: investigating drill bit geometries, feed rates, and spindle speeds

This article investigates the drilling behavior of hemp fiber-reinforced epoxy composites, both unfilled and fly ash-filled. Drilling performance tests were conducted at varying feed rates (8, 16, and 24 mm min⁻¹) and spindle speeds (700, 1400, and 2100 RPM) using three drill geometries: parabolic, 8-facet, and dagger. The fly ash-filled hemp/epoxy composite showed significant reductions in maximum thrust force (25.09%, 19.92%, and 21.43%) and torque (80%, 79.87%, and 59.25%) when drilled with parabolic, 8-facet, and dagger drill bits, respectively, compared to the unfilled composite. The maximum drilling temperature reached 90.6 °C during cutting and decreased to 71.7 °C post-drilling. Overall, the fly ash-filled composites demonstrated superior performance in terms of drilling-induced stresses and damage.