Comparative Analyses of Drilling Force, Temperature, and Damage in Natural and Glass Fiber-Reinforced Al–Epoxy Composites

This study examined the drilling performance of five polymer composite systems: three natural fiber (jute, flax, hemp) composites with aluminum particle-reinforced epoxy, one glass fiber-reinforced composite with the same matrix, and an unreinforced aluminum particle-filled epoxy (Al-epoxy). Drilling experiments were performed at spindle speeds of 1500 and 3000 rpm with feed rates of 50, 75, and 100 mm/min in order to evaluate the effect of cutting parameters on the drilling performance. Cutting zone temperatures were measured using thermocouples embedded within the drill bit's cooling channels, while thrust forces were recorded with a dynamometer. Additionally, hole exit damage and inner hole surface roughness were evaluated to assess machining quality. The results showed that increasing spindle speed reduces thrust forces due to thermal softening of the matrix, whereas natural fiber-reinforced composites generally exhibit higher thrust forces and slightly rougher inner hole surfaces compared to synthetic counterparts. During drilling, the measured thrust forces ranged from 320 to 693 N for the glass fiber-reinforced specimen and from 335 to 702 N for the Al-epoxy specimen, while for natural fiber-reinforced composites the thrust force values were 352-679 N for hemp, 241-719 N for jute, and 571-732 N for flax specimens. Synthetic specimens (glass fiber and Al-epoxy) exhibited comparable cutting temperature ranges (288-371 °C and 248-327 °C, respectively), whereas natural fiber-reinforced composites showed higher and broader temperature ranges of 311-389 °C for hemp, 368-374 °C for jute, and 307-379 °C for flax specimens. The overall results indicated that lower forces were generated during the drilling of synthetic glass fiber-reinforced composites, while among natural fiber-reinforced plastics, flax fiber-reinforced composites stood out by exhibiting a balanced machining response.