Impact of Printing Angle and Layer Height on the Mechanical Strength of PLA Reinforced with Chopped Carbon Fibres Using FDM 3D Printing

This research addresses the inherent limitations of low mechanical strength in FDM-printed materials by studying Carbon Fibre-reinforced Polylactic Acid (PLA-CF) composites. The low strength limitation of PLA-CF in FDM requires identifying the most suitable print angle and layer height parameters. This study maximises its structural robustness, filling a knowledge gap regarding its combined effect on tensile and flexural strength. The main objective was to find the best printing angle and layer height to improve mechanical performance, an important requirement for advancing additive manufacturing applications. A total of 210 FDM-printed specimens of the PLA-CF material were subjected to uniaxial tensile (ASTM D3039) and three-point bending (ASTM D790) tests, systematically varying the printing angles (0-90°) and layer heights of 0.1, 0.2, and 0.3 mm, following a full experimental design matrix. The ANOVA method has been used to determine the significant effect of factors on the established parameters. The findings indicated that both factors had a pronounced effect on the mechanical strength. Printing at lower angles (0° and 15°) provided, on average, greater resistance under tension (up to ~3920 N for a layer height of 0.1 mm), as well as under bending (up to 88.54 N for the same layer height), attributed to favourable fibre alignment and better load distribution. Conversely, higher angles (60° to 90°) drastically reduced strength (tensile failures due to delamination; bending forces as low as 30.02 N for a layer height of 0.3 mm, highlighting the weakness of perpendicular layer interfaces. Furthermore, lower layer height could result in better overall mechanical properties. In conclusion, FDM parameters with low print angles and reduced layer heights are essential for maximising the mechanical robustness and structural integrity of PLA-CF parts, enabling the identification of improved production processes for industrial applications and educational prototypes, among others.