## 3 Taguchi Design versus Central Composite Design  
The design of the experiment is a very strong analysis tool with which it can be modeled and analyzed the influence of the control parameters, which is exerted on the followed response. The standard models are difficult to use, especially on a large number of experiments and when the control factors are varied and numerous [29, 30]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Parameter**} & \multicolumn{2}{c}{**Taguchi’s Method**} & \multicolumn{2}{c}{**Central Composite Design**} \\ \cline{2-4}  & **Value 1** & **Value 2** & **Values** \\ \hline Cutting Speed v (m/min) & 495 & 660 & 495, 530, 570, 610, 660 \\ Cutting Depth a\({}_{\text{p}}\) (mm) & 2 & 4 & 2, 2.5, 3, 3.5, 4 \\ Feed per Tooth f\({}_{\text{z}}\) (mm/tooth) & 0.04 & 0.14 & 0.04, 0.06, 0.08, 0.11, 0.14 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Cutting regime parameters and their values for [PERSON]’s method and central composite design. Figure 6: The measurements made with Mitutoyo SURFTEST SJ-210. This research uses Taguchi methodology and the central composite design to analyze the surface roughness by 7136 aluminum alloy machining as an output variable in end-milling process. The Taguchi method is an effective tool that is widely accepted by industrial engineers to approach the highest possible production at the right price and at the right time. The factors influencing the response are arranged in the form of a lattice square model, this pattern is called an orthogonal array. The design and selection of the orthogonal structure and the reasons for the experiments are the main foundations of the Taguchi process [31]. [PERSON] and [PERSON] [32] noted that the Taguchi method is more focused on shaping the development of production processes to create high-quality output compared to statistical control systems that attempt to control factors affecting quality. [PERSON] [33] demonstrated that the Taguchi method is one of the most effective design test tools to create a high-quality product, developed by [PERSON]. The goals of the orthogonal Taguchi (OA) are a step that gives a small number of very balanced and simultaneous tests. The controls for this test included: cutting speed, cutting depth and feeding of each tooth. A number of eight experiments, as shows the L8 orthogonal array (Table 6), were obtained by applying the design of experiment (DOE) steps. Following the analyzed output data, the optimal machining condition was deducted. The approach of the problem from the central composite design method perspective consists of the three factors involved, which are taken into account with their corresponding values presented in Table 5, in order to determine their influence level exerted on the response. The tests were performed respecting the mentioned cutting regimes of the process factors combinations. Minitab 17 design expert software is used to create the tests plan and analyze all responses in a mathematical format. Overall, eight experiments were carried out for the Taguchi method, each with three R\({}_{\text{a}}\) measurements and a total of 24 measurements (Table 7). For central composite design results, 125 experiments and a total of 375 measurements were carried out (Table 8). To determine the surface roughness equation, the contribution of each parameter and their interactions must first be determined.