Modelling and optimisation of FFF printing parameters for carbon fibre-reinforced PLA

Material extrusion-based fused filament fabrication (FFF) technique is widely used in automobile and biomedical sectors due to its capability to 3D print the complex shapes of composite polymers. This study presents the results of experimental investigation carried out for modelling and optimisation of the FFF printing process for carbon fibre reinforced polylactic acid (PLA-CF). The effects of four significant process parameters, that is, layer thickness (LT), printing speed (PS), infill percentage (IF), and extrusion temperature (ET), are evaluated against the ultimate tensile strength (UTS) and surface roughness (SR) of the fabricated parts. The experiments are designed using a central composite rotatable design. The process is modelled for desired outcomes via regression analysis and optimized using desirability analysis. From analysis of variance, LT and IF are found to be the most significant for UTS, while for surface roughness, LT and PS are the most influential parameters. From SEM analysis, it has been demonstrated that carbon fibres are well-distributed and exhibit excellent interfacial bonding, thereby improving tensile stiffness and load transfer efficiency. From the optical analysis, parts printed with lower LT, PS, and higher IF and ET show smoother transition among layers, which improves UTS and SR. Furthermore, the desirability approach is employed to optimize process parameters using multi-objective approach. The optimized process parameters for achieving higher UTS and lower SR are found to be LT-113 µm, PS-46 mm/s, IF-94%, and ET-233°C. The study findings have practical implications for applications requiring better mechanical properties and surface characteristics simultaneously in 3D printed parts.