## 4 Discussion  
The results obtained with different orientation of samples on the worktable are presented in Figure 6, compared with similar samples fabricated by injection molding (Table 2) [10]. The best results were obtained for samples printed with the horizontal orientation, according to Figure 4, which had 65% of the strength compared with the injection molded samples. Similar results are presented in the literature [8; 9; 11]. Despite the best values of the mechanical strength, this method of sample fabrication has some drawbacks related to the printing of additional supports, extending the printing time. The \"flat\" orientation eliminates the problem of supports and at the same time obtains 60% of the strength noted for injection molded samples. The least resistant samples were oriented vertically to the worktable, having only 33% strength of the injection molded parts. Additionally, we did not observe breakage of the samples but slow delamination of the layers printed, in the same direction as the applied force. Comparing samples printed with different orientations, we can conclude that the samples built along the \(Z\)-axis (vertical) had around 50% of the strength of the remaining samples. Such a phenomenon is due to a significantly lower binding strength between the applied layers (vertical print) compared with the strength of the layer itself (flat, horizontal) [9]. This clearly indicates that the deposition direction of layers in the FDM process (and other additive processes) is of great importance for the strength of the \"printed\" model [12; 13]. This suggests that it is necessary to determine the directions of the load within the printed parts during the design process and apply the most optimal orientation of the printouts on the worktable during the FDM forming process. Figure 10: The influence of the layer thickness applied during the printing process on the mechanical properties of the printed samples. Due to the small difference in the strength values of the samples printed in \"flat\" and \"horizontal\" orientation (less than 5%) and the additional process drawback of printing the support material for horizontal samples, further tests were performed with a flat pattern. The strength tests were performed for the samples with different infill density (Figure 7). Results of the tensile stress test of printed samples with the different infill density are presented in Table 3. An increase in the infill density resulted in an increase in the strength value [7]. At low infill density values of 30%, the strength of the samples was limited to 50% of the samples made by injection molding, and it increased with the larger values of the material added with a higher infill percentage. However, at between 50% and 90% of the infill density, the differences in mechanical strength values were negligible (24.26 and 25.41 MPa, respectively). Only when 100% of infill volume was set did we observe a significant change in the strength value (up to 28.35%). It resulted from a different approach of the slicer algorithm to the type of infill pattern (Figure 2e). Instead of hexagonal infill, layers printed in the XY plane appeared to be printed parallel to the X and Y axes. On one hand, this allowed us to obtain stronger parts, but on the other hand, this created an unexpected input into the experiment, and for this reason, the 100% infill samples were not analyzed further. Setting 100% density of the printout does not mean that the sample structure is identical to that of injection molded parts. It should be noted that there are voids between the consecutively deposited layers and fibers [12; 14; 15; 16]. This means that the FDM printed part is porous in its structure, and therefore it has inferior mechanical strength to elements fabricated from solid material (i.e., injection molded). Such a drawback is inherent for components fabricated with additive manufacturing. Additionally, we have analyzed how the increase in infill density influences the time needed to make a single sample.