OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 7 2 5 Fig. 6, a shows that minimum Fx is observed at 10 % SiC volume fraction, while maximum occurs at higher SiC volume fractions; similarly, as feed increases, Fx also increases. It has been observed from Fig. 6, b that Fx varies according to Q, with maximum Fx at 150 ml/h and 0.2 mm/rev, while minimum at 90 ml/h and 0.1 mm/rev. Fig. 6, c shows that maximum Fx is observed at 150 ml/hr and 30 % Vf. It has been observed that as Q increases, Fx also increases; a similar trend has been observed for Vf. However, a rapid increase in Fx occurs as Vf increases from 10 to 20 %, while no significant rise is found after 20 % Vf. Fig. 6, a and b depict that as f increases from 0.1 to 0.2 mm/rev, Fx also increases rapidly. These results are in agreement with reports by Gaitonde et al. [11]. Fig. 6, a and c indicate that as Vf increases from 10 to 30 %, Fx also increases rapidly; however, no significant difference has been observed between 20 and 30 % Vf – similar findings were reported by Gaitonde et al. [12]. It has been seen from Fig. 6, b and c that minimum Fx is obtained at low Q (90 ml/hr), while maximum is at high Q (150 ml/hr). a b c Fig. 6. Effect of cutting speed, feed, sic volume fraction and flow rate on thrust force under NMQL conditions Like thrust force, torque also affects the quality of the hole generated. During drilling, the sharp cutting edges over the periphery are often blunt and produce friction by rubbing rather than cutting [18]. The effect of process parameters on torque is shown in Fig. 7. Fig. 7, a indicates that as Vf increases from 10 to 30 %, torque also increases rapidly; however, after 20 % Vf, torque shows a slight decrease. It has also been seen that minimum torque occurs at low feed rate and flow rate combination (90 ml/h and 0.1 mm/rev), while maximum occurs at 150 ml/h and 0.2 mm/rev. In addition, Fig. 7, b shows that as feed increases from 0.1 to 0.2 mm/rev, torque also increases. Surface roughness is an indicator of finely spacedmicro-irregularities on the surface texture, consisting of three parts: roughness, waviness, and form [24]. It evaluates the surface finish to assess surface irregularities of the workpiece due to machining. It is normally determined as the average roughness (Ra), commonly used in the industry. Surface roughness is among the essential aspects of hole quality, where greater surface roughness causes additional wear and fatigue in the material, which directly impacts the production process and cost [21]. It plays a key role in manufacturing and is a major element in assessing machining accuracy [22]. From Fig. 8, a, it has been observed that maximum Ra is seen at 10 % Vf, while it decreases sharply at 30 % Vf. Also, as feed rate increases from 0.1 to 0.2 mm/rev, Ra increases. Fig. 8, b shows that as Q increases from 90 to 150 ml/hr, Ra also increases sharply. Maximum Ra is observed at low Vf and high Q (10 % Vf and 150 ml/h), while minimum at high Vf and high Q. Fig. 8, c shows maximum Ra at 10 %
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