OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 2 5 Fig. 13. Comparison of variation of burr height (Bh) with feed (f) and SiC volume fraction in drilling Fig. 14. Comparison of variation of circularity (mm) with cutting speed (Vc) and SiC volume fraction in drilling Fig. 15 shows that at low cutting speeds, MQL performs better, while at higher speeds NMQL gives better results. At high speeds, lack of heat transfer degrades surface quality due to retained heat. Graphene oxide nanofluids, with higher thermal conductivity, improve heat transfer, reduce friction and temperature, and yield better surface finish. High temperature is eliminated from the machining area due to high thermal conductivity. The ball bearing effect of nanoparticles under MQL decreases friction and provides superior cooling and lubrication at the tool-chip interface, reducing tool wear and surface roughness [4]. In this study, the main wear mechanism was abrasion, although adhesion wear was also observed. Different wear types may occur simultaneously or one may dominate due to friction between tool and workpiece. SEM results in Fig. 16, a show the drill tool micrograph after NMQL cooling, and Fig. 16, b shows Fig. 15. Comparison of variation of surface roughness (Ra) with cutting speed (Vc) and SiC volume fraction in drilling
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