## 3 Results, Analysis, and Discussion
### Analysis and Discussion
Arithmetical Mean Roughness, _Ra_ (\(\mu\)m), measured in each plate at the entry and at the exit zones of the holes. Adapted from [18]. Similarly, and based on the analysis of the results presented by [PERSON] and his collaborators in 2018 [18] (Figure 6), the following preliminary conclusions can be drawn from the analysis performed in the present study:  
* It is possible to obtain all \(Ra\) (\(\mu\)m) values below the maximum limits of the strict tolerances demanded in the aeronautical sector for a re-drilling repair of hybrid Mg-Ti-Mg components by using sustainable lubrication systems. In particular, using the cutting parameters defined in tests 3, 5, and 7, all \(Ra\) (\(\mu\)m) values are below 1.6 \(\mu\)m.
* The factor with a significant effect on the response variable \(Ra\) (\(\mu\)m) is the Location Regarding Insert, \(LRI\), (32.3%), and the interactions \(LRI\)\({}^{*}T\) (39%) and \(T\)\({}^{*}f\) (28.7%). * The conditions of test 1 would allow the re-drilling of a hybrid compound made up of two titanium and magnesium plates, in that order, each 7.5 mm thick. * Test 4 might re-drill together three Mg-Ti-Mg plates with thicknesses of 7.5 mm for magnesium and 15 mm for titanium, making slight adjustments to the process parameters, since the roughness values in terms of \(Ra\) (\(\mu\)m) for magnesium, on both plates, are close to the standard values in the aeronautical sector. As novelties provided by the joint analysis of the present work, we can state that for the Mg-Al combination, 15 mm Mg plates and 7.5 mm Al plates are generally more suitable, whereas, for Mg-Ti combinations, 7.5 mm Mg plates and 15 mm Ti plates seem more favorable. These conclusions make it possible to design new configurations of hybrid multimaterial specimens to obtain more information in future tests. This information will lead to better comprehension of the relationship between the quality of the final machining and the thickness of the plates of magnesium-based multimaterials, a possible directional influence on machining, and to continue progressing in the development of sustainable machining techniques applicable to magnesium-based multimaterial components in the aeronautical and/or automotive sectors. Therefore, new tests are proposed on Mg-Al-Mg and Mg-Ti-Mg specimens with the same cutting parameters in both, and a higher number of levels for each analyzed factor to verify the similarities, or not, of the results obtained. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **Squares Sum** & **DF \({}^{*}\)** & **Mean Square** & **F** & **Sig.** \\ \hline Corrected model & 8.487 \({}^{\text{a}}\) & 11 & 0.772 & 2.235 & 0.034 \\ Intercept & 0.567 & 1 & 0.567 & 1.643 & 0.208 \\ LRI & 2.440 & 2 & 1.220 & 3.534 & 0.040 \\ T & 0.022 & 1 & 0.022 & 0.063 & 0.804 \\ f & 0.017 & 1 & 0.017 & 0.049 & 0.826 \\ \(LRI\)\({}^{*}T\) & 2.948 & 2 & 1.474 & 4.270 & 0.022 \\ \(LRI\)\({}^{*}f\) & 0.243 & 2 & 0.121 & 0.352 & 0.706 \\ \(T\)\({}^{*}f\) & 2.166 & 1 & 2.166 & 6.275 & 0.017 \\ \(LRI\)\({}^{*}T\)\({}^{*}f\) & 0.651 & 2 & 0.326 & 0.943 & 0.399 \\ Error & 12.429 & 36 & 0.345 & & \\ Total & 21.483 & 48 & & & \\ Corrected total & 20.916 & 47 & & & \\ \hline \hline \end{tabular} \({}^{*}\)DF: degrees of freedom. (\({}^{\text{a}}\) R Squared = 0.406 (Adjusted R Squared = 0.224)).  
\end{table} 
Table 10: Mg-Ti-Mg test. Last ANOVA iteration for Ln_Ra_ values. Adapted from [18]. Likewise, it is proposed to redesign, manufacture, and test with similar cutting parameters new specimens of two and three plates of magnesium, aluminum, and titanium. More specifically, specimens made up of two Mg-Al and Mg-Ti plates, and of three Mg-Al-Mg and Mg-Ti-Mg plates, taking into account the results obtained in this work, mentioned above, concerning the thicknesses of the plates, which will be made with the same cutting parameters in both specimens and, regarding their dimensioning, with the values included in the European standards [66,67] and international ISO standards on rivets for aerospace application [68,69].