OBRABOTKAMETALLOV technology Vol. 26 No. 3 2024 Ta b l e 4 ANOVA for surface roughness, microhardness, and roundness Factors Surface roughness (Ra) Microhardness (HV) Roundness error (Re) R-squared 0.9769 0.9152 0.9407 Adj. R-Squared 0.956 0.8389 0.8873 Pred. R-Squared 0.8472 0.855 0.8933 Adeq. Precision 19.328 15.464 16.002 Model F-value 46.91 11.99 17.62 decreasing when the cutting speed exceeds 280–300 rpm. On the other hand, roundness error can be seen as decreasing with an increase in the cutting speed. Fig. 2b depicts the variation of measured responses varying with feed, plotted using cutting speed of 300 rpm and three passes. And Fig. 2c depicts the variation of measured responses depending on the number of passes, plotted using a cutting speed value 300 rpm and feed rate of 0.2 mm/rev. From Fig. 2b, the optimum values for the feed-dependent responses can be seen. The minimum surface roughness and roundness error can be obtained using feed in the range of 0.18–0.22 mm/rev, a cutting speed of 300 rpm, and three passes. However, maximum microhardness can be obtained using higher feed values. When the feed is increased to 0.2 mm/rev, a decrease in surface roughness and microhardness can be observed, as well as an increase in the roundness deviation. However, these responses can be seen as changing its trends beyond the feed value of 0.2 mm/rev. The minimum roundness error and maximum microhardness can be obtained by using either of lower or higher feed values. However, minimum surface roughness can be obtained using feed value in the range of 0.18–0.22 mm/rev. Surface roughness can be seen as decreasing with an increase in number of passes. However, no significant benefit in lowering surface roughness can be seen beyond using four number of passes. Roundness error can be minimized using higher number of passes. Similarly, a maximum microhardness can be obtained using higher number of passes. The ANOVA results for the F-values of surface roughness, microhardness, and roundness error are shown in Table 5. The factors that had a significant effect on the results are underlined. Similarly, percentage contributions of different elements, obtained by dividing the corresponding element F-value by the total F-value, are also given in Table 5. It can be seen that, surface roughness is mainly affected by the higher feed rate (almost 30.76 %), followed by higher cutting speed and interaction effects of the cutting speed and the number of passes (nearly 20 % and 15.88 %, respectively), and the cutting speed and the feed have little effect. However, it can be considered that the number of passes has a great effect on reducing the surface roughness. The percentage contributions of these significant model terms are shown in bold-case in Table 5. a b c Fig. 2. Responses varying with (a) Cutting sped, (b) Feed, and (c) Number of passes
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