## 5 Results  
The hard-turning operation with both tool materials were controlled by three factors, namely the cutting speed, feed rate, and depth of cut. Therefore, these parameters generally affected the possible results of the machining. For that reason, the mean behaviors of the cutting temperature were evaluated using dispersion analysis and a main effect plot. The main effect plot shows a relative change from the center point of the experiment. After the dispersion analysis, the adequacy of the model (Fa) and the significance of the input parameters (Fr\({}_{0}\), Fr\({}_{1}\), Fr\({}_{2}\) and Fr\({}_{3}\)) were determined and are presented in Table 5. Based on this analysis and the obtained statistical parameters, it can be concluded that the obtained values for the adequacy of the empirical models and the significance of the input parameters were sufficiently reliable. It is evident from Figure 4a that the increase in cutting speed caused an increase in the cutting temperature. The reason for the increase in cutting temperature was due to the conversion of mechanical energy (rotation of spindle) into heat energy. The cutting speed with the CBN tool had a similar effect (Figure 4b). The effects of the feed on the cutting temperature for both tool material were contrary to expectations. For instance, an increase in feed rate caused a significant increase in cutting temperature. Lastly, depth of cut also effected the cutting temperature, especially when turning with an HM tool, while with CBN, it showed a smaller effect. This can be explained by the fact that the tool material of cubic boron nitride has better thermal conductivity. This was also confirmed by experiments that showed that generally higher temperatures occur with HM tools [12]. The maximum temperature for HM was 350 \({}^{\circ}\)C, while for CBN, it was 169 \({}^{\circ}\)C.  
Compared to literature sources, the cutting temperatures obtained in this paper were lower. This happened by adopting a medium cutting speed according to the manufacturer's recommendations as a way to measure temperature. The use of thermocouples gave a more realistic temperature, but on the economic side, it is quite expensive. It is also appreciable for HM tool that all three input parameters had a significant effect on cutting temperature. Compared to these machining parameters, the depth of cut played a small role in defining cutting temperature values, especially with CBN tools. Hence, during optimization, the change in cutting speed, feed, and depth of cut were most significant to favorably align the value of the responses, while for CBN tools, one should pay attention to only the cutting speed and feed. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Model Adequacy**} & \multicolumn{2}{c}{**HM \(\Theta\) (\({}^{\circ}\)C)**} & **CBN \(\Theta\) (\({}^{\circ}\)C)** \\ \cline{3-4}  & \multicolumn{2}{c}{**Fa = 4.20467**} & **Fa = 3.77465** \\ \hline \multirow{4}{*}{**Significance**} & F\({}_{\text{ro}}\) & 679937.42 & 214918.52 \\ \cline{2-4}  & Fr\({}_{1}\) (v) & 105.27 & 71.11 \\ \cline{1-1} \cline{2-4}  & Fr\({}_{2}\) (f) & 72.60 & 35.71 \\ \cline{1-1} \cline{2-4}  & Fr\({}_{3}\) (a) & 12.62 & 8.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Adequacy of models and significance of parameters. The main contribution of this paper is the application of ANFIS intelligent techniques in modelling cutting temperature. The model results obtained for the cutting temperature are shown in Table 6. In order to verify the reliability of the adopted ANFIS model, a calculation of absolute relative errors between experimental and model data was performed. The absolute relative error was calculated for the training, testing, and validation data. All errors were within the allowed limits, i.e., less than 10%, and the adopted model can be used with a high reliability for the analysis and prediction of cutting temperature, as well as the optimization of input parameters. Another ANFIS model for reliability confirmation is shown using the correlation diagrams.