OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 2 5 It has been observed from Fig. 9, a that minimum circularity (Cr) is obtained at 0.1 mm/rev and 10 % SiC volume fraction, while maximum occurs at 30 % SiC volume fraction and 0.2 mm/rev. Fig. 9, b shows minimum Cr at 10 % SiC volume fraction and maximum at 30 %, with Cr increasing with flow rate (minimum at 90 ml/h, maximum at 150 ml/h). Fig. 9, a shows minimum Cr at 0.1 mm/rev and maximum at 0.2 mm/rev; Cr increases with feed rate, likely due to increased cutting forces. Faster insertion of the drilling tool through the workpiece due to higher feed rate increases hole deformations and vibrations in the cutting tool, resulting in higher circularity errors. Fig. 9, a and b show Cr increases rapidly as Vf changes from 10 to 30 %, with minimum Cr at 10 % and maximum at 30 %. a b Fig. 9. Effect of cutting speed, feed rate, SiC volume fraction and flow rate on circularity under NMQL condition Burr is plastically deformed material produced on the edge of the component during drilling. Burrs form and spread circumferentially as the drill feeds into the workpiece. The size of the exit burr is a performance measure of the drilling process that determines the quality of the finished product. It is essential to minimize burr formation at manufacturing stage by choosing proper drilling process parameters. Fig. 10, a shows that as SiC volume fraction increases from 10 to 20 %, burr height (Bh) increases; however, after 20 % it decreases. As flow rate increases, Bh increases. Maximum Bh is obtained at 20 % Vf and 150 ml/h, while minimum at 10 % Vf and 90 ml/h. Fig. 10, b shows no significant effect of cutting speed and feed on Bh, although maximum burr height is observed at low feed and cutting speed (60 m/min and 0.1 mm/rev). Fig. 10, a shows Bh increases with Q from 90 to 150 ml/h due to excessive fluid and nanoparticles at the workpiece-tool and chip-tool interface, which increases cutting force and ploughing during drilling, thus increasing burr height [21]. Bh increases as Vf changes from 10 to 20 %, but decreases from 20 to 30 %. Fig. 10, b shows no significant effect of cutting speed on Bh, although a slight increase at 60 m/min is observed. Comparison of MQL and NMQL conditions at different cutting speeds and SiC volume fractions was conducted to understand the effect of graphene oxide nanoparticles mixed with Undi oil. Fig. 11 shows that at 10 % SiC volume fraction, MQL gives better results compared to NMQL, while NMQL performs equally or better at 20 and 30 % SiC volume fractions. This is because graphene oxide nanoparticles have a b Fig. 10. Effect of cutting speed, feed rate, SiC volume fraction and flow rate on burr height under NMQL condition
RkJQdWJsaXNoZXIy MTk0ODM1