## 2 Materials and Methods
### Leakage and Roughness Testing  
To find the relations between the surface, leakage, machining, and clamping force, it was necessary to use appropriate devices which allow for leakage tests at various processing parameters, generating different surface qualities and various compressive forces of the joint. First, the topography surfaces of the tested samples were determined, then the tested parts were fixed in the testing machine which provides the required compressive force to the samples. The second step of the study, after force stabilization, was the leak test, which was the last step in the study. The surface area of the tested surface subject is 88 mm\({}^{2}\). The measurement of the surface topography was performed using the Alicona Infinite Focus G5 type focal differentiation microscope. The components with the use of the device with 20x lens can be measured in high vertical resolution up to 50 nm and in high vertical repeatability up to 10 nm. Furthermore, the research was divided into two stages. The first phase was to select the analysis pairs with the same roughness value (Ra parameter), and the next step was to segregate the surfaces in the peer-to-peer system. For each type of set, an analysis of the surface topography was performed to determine the parameter influencing the amount of leakage at a given compression force (FS). The test was carried out for a set pressure of 2 \(\pm\) 0.02 bar. The volume of the system was 21.25 cm\({}^{3}\). The experiment was performed for the conditions presented in Table 4. The first is to fill the system, the second is to stabilize it for 9 s, the third step is the 1 s test, and the final step is to empty the test chamber. During the test, one of the samples was fixed with the mounting plate, while the other was movable in relation to the first. This construction allowed the parts to be pressed against each other at a given value. Consequently, this allowed us to obtain characteristics showing the dependence of the clamping force on the obtained leakage and to determine the size of the leak depending on the surface topography. Moreover, it allowed the evaluation of the force at which the system stabilized and allowed the test procedure to be performed (Figure 3). The force sensor used to control the load provided during the leak test was HBM \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Test** & **System** & **Filling Time** & **Stabilization Time** & **Test Time** & **Emptying Time** \\
**Pressure** & **Volume** & **Filling Time** & **Time** & **Test Time** & **Time** \\ \hline
2 bar & 21.25 cm\({}^{3}\) & 1 s & 9 s & 1 s & \textless{1 s} \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Values adopted for the leak test. Figure 2: A cross-sectional view of the part subjected to leakage tests. RSCC3/2T of error \(\pm\)0.25% FSO with the RM4220 transducer of accuracy class 0.1. The measurement system shown below has a combined measurement error of \(\pm\)0.35% FSO, it provides a value of \(\pm\)70 N. The maximum force that can be provided to the assembled kit for the leak test is 20,000 N.  
The first tests were carried out for twin samples (with the same roughness value). The tests were performed for various forces to obtain the expected leakage threshold of the tested elements. The stand for testing the leakage test was based on the ATEQ F620 leak detector. The device measures the pressure drop generated in a system with a known volume. The device was equipped with an electronic regulation of the inlet pressure. The tests were characterized by the leakage value associated with the gap between the surfaces. The concept of checking the tightness against the tested parts was based on the absolute pressure drop measurement method (Figure 4).