## 3 Results and Discussion
### Experimental Verification of the Proposed Control Method  
The device that implements the developed method of temperature control was integrated into an FDM-printer. To test the performance of the developed method, a number of test samples were made from materials, such as polyamide PA 6, PC, and PEEK. Tensile stress test was carried out in accordance with the requirements of State All-Union standard 11262-2017 [69], according to which test samples (type 1) were made with overall dimensions: 115 \(\times\) 25 \(\times\) 2 mm. The test samples were printed with a software-specified 100% filling of the internal volume, with the printing parameters presented in Table 5. The external appearance of some test samples after testing is shown in Figure 13. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Material**} & \multirow{2}{*}{\begin{tabular}{c} **Nozzle** \\ **Temperature,** \\ \({}^{\circ}\)**C** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Bed** \\ **Temperature,** \\ \({}^{\circ}\)**C** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Raster Angle/No.** \\ **Temperature,** \\ \({}^{\circ}\)**C** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Deposition** \\ **Speed, mm/s** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Nozzle** \\ **Diameter,** \\ **mm** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Layer** \\ **Thickness,** \\ **mm** \\ \end{tabular} } \\ \hline PA 6 & 250 & 130 & 1 & 2 & 40 & \\ \hline PC & 240 & 120 & 1 & 2 & 40 & 0.6 & 0.2 \\ \hline PEEK & 440 & 140 & 1 & 2 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: FDM 3d-printing process parameters. Figure 12: Experimental and estimated transient response of a closed-loop ACS for 110, 260, 440, 600 and 750 \({}^{\circ}\)C setpoints. The tests were carried out using an Instron 5882 testing machine with a non-contacting video extensometer Instron Ave at the ambient temperature of 24 \({}^{\circ}\)C, 50% humidity at the speed of 2 mm/min. From each material, 4 samples were made, differing in the attitude of the layers (the angle of filling the internal volume), as well as the extrusion temperature. Tensile stress test results are presented in Table 6. Figure 14 shows the stress-strain behavior for the deposited samples under tensile stress. The test results show that tensile strength values are not lower than those known from the literature. At the same time, for samples made of PLA, ABS, PC, and PA 6, an increase in tensile strength up to 20% is observed at strain values comparable with those known from the literature. The test results for PLA and ABS samples, as well as the results of optical microscopy of the fracture surface of these specimens, are presented in our previous article [53]. A comparison was made with the results of studies in which the printing parameters were used similar to those given in Table 5 and some approaches to improving printing quality described in the introduction were used. For example, in [8; 40; 41; 70; 71; 72], the results are presented for samples made from ABS, in [8; 42; 43; 44; 73] for PLA, for PA 6 in [10; 74], and for PC in [72; 75; 76]. To raise efficiency when operating with PEEK, additional research and optimization of printing parameters are required, considering the results, recommendations, and conclusions contained in the literature [5; 11; 77]. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Material** & **No.** & **Tensile Strength, MPa** & **Elongation at Maximum Tensile Stress, \%** \\ \hline \multirow{4}{*}{PA 6} & 1 & 48.37 & 17.1 \\  & 2 & 42.42 & 14.5 \\  & 3 & 45.95 & 13.3 \\  & 4 & 44.73 & 13.5 \\ \hline \multirow{4}{*}{PC} & 1 & 68.13 & 5.7 \\  & 2 & 68.48 & 6.2 \\ \cline{1-1}  & 3 & 64.94 & 6.1 \\ \cline{1-1}  & 4 & 65.24 & 5.6 \\ \hline \multirow{4}{*}{PEEK} & 1 & 89.91 & 4.7 \\  & 2 & 80.72 & 4.3 \\ \cline{1-1}  & 3 & 77.34 & 4.4 \\ \cline{1-1}  & 4 & 71.56 & 4.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Tensile stress test results.