The Effect of Deposition Orientation and Thickness on the Flexural Strength of PLA Plate Produced by 3D Printing

In this study, the influence of deposition orientation and specimen thickness on the flexural strength of 3D-printed polylactic acid (PLA) plates was examined. The samples were fabricated using the Fused Deposition Modeling (FDM) method with five deposition orientations—0–0, 0–90, 45–45, 90–90, and honeycomb—and two thicknesses of 3.2 mm and 6.4 mm. Flexural testing followed the ASTM D790-03 standard procedure. The results indicate that deposition orientation plays a decisive role in determining the mechanical response. Specimens printed at 0–0, where filaments run parallel to the loading axis, achieved the highest flexural strength (103.10 ± 6.29 MPa at 3.2 mm thickness), while honeycomb structures exhibited the lowest values (around 17.5 MPa). A two-way ANOVA confirmed a highly significant effect of deposition orientation on flexural strength (p< 0.001). Although the main effect of thickness alone was not statistically significant (p = 0.153), the interaction between orientation and thickness was significant (p< 0.001), suggesting that the impact of thickness depends on the printing direction. Post-hoc tests further showed that only the 0–0 and 90–90 orientations displayed meaningful differences between thickness levels. Overall, the findings highlight that the mechanical anisotropy of FDM-printed PLA is largely controlled by filament alignment and interlayer bonding. By selecting appropriate deposition orientation and part thickness, the flexural strength of printed PLA components can be notably improved, providing practical guidance for engineers in designing reliable, load-bearing 3D-printed parts.