OBRABOTKAMETALLOV MATERIAL SCIENCE Том 23 № 3 2021 EQUIPMEN . INSTRUM TS Vol. 7 No. 2 2025 a b c Fig. 8. Effect of cutting speed, feed rate, SiC volume fraction and flow rate on surface roughness under NMQL conditions a b Fig. 7. Effect of cutting speed, feed, SiC volume fraction and flow rate on torque under NMQL conditions Vf, while it decreases sharply as Vf increases to 30 %. Also, maximum Ra is obtained at 60 m/min, while minimum is obtained at 120 m/min. Fig. 8, a shows that as feed rate increases from 0.1 to 0.2 mm/rev, Ra shows a slightly increasing trend. Lower feed values result in minimum thrust force during drilling, which is one reason for better surface finish at low feed rate [2]. It has been observed from Fig. 8, b that Ra is maximum at 10 % Vf while minimum at 30 % Vf. The increase in Vf decreases Ra, likely caused by increased brittleness and consequent demise of the built-up edge (BUE) in machining composite materials (Gaitonde et al., 2009). Fig. 8, b also shows that as Q increases from 90 to 150 ml/hr, Ra also increases, confirming that at low Q, MQL can provide better Ra in drilling. This is possibly due to reduced BUE formation from the mist action at the tool-workpiece interface. Fig. 8, c shows that as cutting speed changes from 60 m/min to 120 m/min, Ra decreases. This trend can be explained by the fact that as cutting speed increases, cutting temperature rises, leading to material softening and subsequent reduction in Ra. Circularity is defined as the degree of roundness of a circular hole. Circularity defines how close a component should be to a perfect circle. Circularity, often called roundness, is a 2-dimensional tolerance that determines the overall shape of a circle and ensures it is not too oval, rectangular, or irregular [2].
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