# Sustainability-Based Analysis of Conventional to High-Speed Machining of Al 6061-T6 Alloy
## 6 Consolidated Results  
The primary objective of this research was to perform a comprehensive sustainability analysis of the turning of Al 6061-T6 alloys at varying cutting conditions. As surface roughness (Ra) has been extensively studied by past researchers for many decades, a special emphasis was given to SCE. Therefore, to obtain a holistic picture of the evolution of SCE consumption within the three machining regions (conventional, transitional, and high-speed machining), the results have been consolidated (Figures 11-15). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & & & \multicolumn{4}{c}{**Levels of Machining Variables**} \\ \hline \multirow{2}{*}{**Responses**} & & **Ave.** & **Speed** & **Feed** & **Depth of** \\  & & **Value** & **(m/min)** & **(mm/rev)** & **Cut (mm)** \\ \hline \multirow{2}{*}{Specific cutting energy (J/mm\({}^{3}\))} & Best & 0.33 & 2000 & 0.4 & 4 \\  & Worst & 0.78 & 2500 & 0.1 & 1 \\ \multirow{2}{*}{Surface roughness (\(\upmu\)m)} & Best & 1.28 & 2500 & 0.1 & 1 \\  & Worst & 7.96 & 1750 & 0.4 & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Results of confirmatory experiments for high-speed machining. Figure 10: Main effect plot showing the influence of cutting parameters on Ra in HSM. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Variable** & **DOF** & **Seq. SS** & **Adj. MS** & **F-Value** & \(p\)**-Value** & **CR (\%)** \\ \hline \(v\) (m/min) & 3 & 4.166 & 1.38866667 & 7.09 & 0.001 & 1.70\% \\ \(f\) (mm/rev) & 3 & 194.32 & 64.7733333 & 330.91 & 0.000 & 91.86\% \\ \(d\) (mm) & 3 & 4.968 & 1.656 & 8.46 & 0.000 & 2.08\% \\ Error & 38 & 7.438 & 0.195736842 & & & 4.36\% \\ Total & 47 & 210.892 & & & & 100.00\% \\ \hline \hline \end{tabular}
\end{table} 
Table 14: Analysis of variance and percentage contribution results for Ra. A general trend of drop in SCE can be observed within the conventional speed machining (CSM) region and the transitional speed machining (TSM) region (Figure 11). However, the drop in SCE is observed to be highest in the CSM region (11.8%), followed by the TSM region (6.7%). The trend followed by SCE in the high-speed machining (HSM) region is parabolic in nature. SCE first dropped by 3.8% when cutting speed was increased to 2000 m/min. Beyond this point, a sharp increase (about 17%) in SCE was observed. The parabolic trend signifies the presence of an optimum value of cutting speed over which the SCE is minimum. In the present study, the maximum value of SCE was observed at 125 m/min and the minimum value at 2000 m/min. In the case of the effect of feed on SCE (Figure 12), a drastic reduction in SCE is observed in all three machining regions. In the CSM region, the drop in SCE from feed of 0.1 mm/rev to 0.4 mm/rev has been observed to be about 36%, whereas in the TSM region, the drop in SCE with an increase in feed has been observed to be 30%. The maximum drop in SCE has been observed in the HSM region, where a reduction of around 54% in SCE is observed when feed is increased from 0.1 to 0.4 mm/rev. The high significance of feed on SCE can be explained with the help of chip mechanics and the cutting process mechanism. An increase in feed while keeping the cutting speed at a constant value results in an increase in chip thickness, chip thickness ratio, and, consequently, high shear  
Figure 11: Effect of cutting speed on SCE. Figure 12: Effect of feed on SCE in three machining regions. plane angle [43]. Additionally, with the increase in feed, the cutting process mechanism gradually shifts from the rubbing/ploughing dominated zone to a more efficient shearing zone [52]. The energy required to remove material at the shear plane (specific shearing energy) decreases, and the overall efficiency of the cutting process increases in the shearing-process-dominated cutting zone [10]. The high significance of feed for specific energy consumption has been reported in the literature for turning operations [16; 17].