## 4 Results and Discussion  
Cutting force, surface roughness, and tool wear in the milling of Ti-6242S were investigated by using different cutting parameters. The cutting force diagram obtained from Kistler DynoWare was given in Figure 2 and the tool wear (VB) was given in Figure 3 for the 15 m/min cutting speed, 0.08 mm/rev feed rate, and 1.5 mm depth of cut. The cutting force was calculated by using Equation (13). \[F=\left(Fx^{2}+Fy^{2}+Fz^{2}\right)^{\frac{1}{2}} \tag{13}\]  
Cutting forces, tool wear, and surface roughness values were experimentally determined for all cutting parameters. The predicted values were obtained from ANN and RSM using the experimental results. Optimum weights depending on training of ANN were found by Equations (1)-(10). Then these optimum weights were written in Equations (1)-(3). Thus, the estimated cutting parameters were  
Figure 3: Tool wear in milling Ti-6242S. Figure 2: Cutting force diagram in milling Ti-6242S. calculated. Mathematical models related to cutting force, surface roughness, and tool wear were produced by Equation (11) or Equation (12) in RSM. These are given in Equations (14)-(16). \[F =17.75+5.75V+2868.75f-4a-0.23V^{2}-9218.75f^{2}+7a^{2}-27.5 Vf-0.2 Va-75 fa \tag{14}\] \[Ra =1.69-0.042V-0.96f-0.57a+6.3V^{2}-10.47f^{2}+0.15a^{2}+2 Vf+6 Va+1.62 fa\] (15) \[VB =0.07+2.95V+0.168f-2a-V^{2}-1.89f^{2}+9a^{2}+0.018 Vf+2 Va+0.025 fa \tag{16}\]  
where \(F\) is cutting force, \(Ra\) is surface roughness, \(VB\) is tool wear, \(V\) is cutting speed, \(f\) is feed rate, and \(a\) is depth of cut. The predicted values obtained from ANN and RSM together with experimental results are given in Table 4. Predicted and actual values of cutting force, surface roughness, and tool wear are given in Figures 4-6, respectively. When the cutting force, surface roughness, and tool wear were examined in Figures 4-6, it was seen that predicted and actual values was close to the absolute line for ANN and RSM. The results of experimental were compared to the results of ANN and RSM for cutting force, surface roughness, and tool wear in Figures 7-9, respectively. Figure 4: Predicted versus actual values for cutting forces (**a**) ANN; (**b**) RSM. Figure 5: Predicted versus actual values for surface roughness (**a**) ANN; (**b**) RSM. Figure 6: Predicted versus actual values for tool wear (**a**) ANN; (**b**) RSM. Figure 3:0 Comparison of surface roughness of experimental data, ANN, and RSM. (**a**) Cutting Speed 20 m/min; Depth of Cut: 2 mm; (**b**) Feed Rate 0.08 m/min; Depth of Cut: 1.5 mm; (**c**) Cutting Speed: 10 m/min; Feed Rate: 0.12 mm/rev. Figure 3:1 Comparison of cutting forces of experimental data, ANN, and RSM. (**a**) Cutting Speed 20 m/min; Depth of Cut: 2 mm; (**b**) Feed Rate 0.08 m/min; Depth of Cut: 1.5 mm; (**c**) Cutting Speed: 10 m/min; Feed Rate: 0.12 mm/rev. As seen in Figure 7, obtained values from ANN and RSM for cutting force were very close to the experiment results. When the feed rate and the depth of cut increased, the cutting force increased. In this case, the metal removal rate increased. Thus, it was considered that the cutting force increased. On the other hand, higher cutting speed reduced the cutting force. It was considered that the cutting force reduced because increased of the cutting speed was led to increase of removed chip cross section. Maximum deviation between experimental results and ANN was found as 11.48% at 25 th experiment. On the other hand, Maximum deviation between experimental results and RSM was found as 4.95% at ninth experiment for cutting forces. However, total average deviations obtained from all experimental studies were found 0.074% and 0.53% for ANN and RSM, respectively. From Figure 8, it was seen that experiment results were be closed to obtained values from ANN and RSM for surface roughness. It was seen that obtained values from ANN and RSM were close to experimental results for surface roughness. Surface roughness reduced with increasing of the cutting speed and it increased with increasing of the feed rate and the depth of cut.