Influence of Cooling Lubricants and Structural Parameters on the Tensile Properties of FFF 3D-Printed PLA and PLA/Carbon Fiber Composites

This study addresses the lack of comprehensive understanding regarding how both structural printing parameters and environmental factors influence the mechanical properties of additively manufactured polymer and composite materials. The main problem stems from insufficient data on the combined effects of infill density, number of perimeters, layer height, and exposure to cooling lubricants on the tensile performance of 3D-printed products, which is crucial for their reliable application in demanding environments. In this research, the influence of four critical parameters—infill density, number of perimeters, layer height, and exposure to cooling lubricants—on the tensile properties of specimens produced by fused filament fabrication (FFF), also known as fused deposition modeling (FDM), from polylactic acid (PLA) and polylactic acid reinforced with carbon fibers (PLA+CF) was investigated. Tensile tests were performed in accordance with ISO 527-2 on specimens printed with honeycomb infill structures under controlled process conditions. The results show that increasing infill density from 40% to 100% led to an approximately 60% increase in tensile strength for both PLA (from 30.75 MPa to 49.11 MPa) and PLA reinforced with carbon fibers (PLA+CF; from 17.75 MPa to 28.72 MPa). Similarly, increasing the number of perimeters from 1 to 3 resulted in a 51% improvement in tensile strength for PLA and 50% for PLA+CF. Reducing layer height from 0.40 mm to 0.20 mm improved tensile strength by 5.4% for PLA and 3.1% for PLA+CF, with more pronounced gains in stiffness observed in the composite material. Exposure to cooling lubricants led to mechanical degradation: after 30 days, PLA exhibited a 15.2% decrease in tensile strength and a 3.4% reduction in Young’s modulus, while PLA+CF showed an 18.6% decrease in strength and a 19.5% drop in modulus. These findings underscore the significant impact of both structural printing parameters and environmental exposure on tailoring the mechanical properties of FFF-printed materials, particularly when comparing unfilled PLA with carbon fiber-reinforced PLA.