Fused Filament Fabrication (FFF), also known as Fused Deposition Modelling (FDM), is one of the innovative 3D printing technologies for fabricating complex components and products. Mechanical properties of 3D-printed components mostly depend on intricate process parameters of 3D printing. This study experimentally investigates the effects of four key process parameters, including layer thickness, raster angle, feed rate, and nozzle temperature, on the tensile properties and interfacial bonding behaviours of FFF printed Polylactic Acid (PLA), and their failure mechanisms. The effect of the key parameters on surface roughness is also evaluated, which is critical for enhancing manufacturing and material performance, expecting to provide a potential guide for optimisation of the FFF printing process for improving product quality. The experimental results demonstrate that tensile strength improves up to 10 and 7% with increasing nozzle temperature (200 °C to 220 °C) and low feed rate (60 mm/sec to 40 mm/sec) during the 3D printing process. The tensile strength increases up to 12% with decreasing layer thickness (0.4 mm to 0.2 mm) and 40% with decreasing raster angle (90° to 0°). The experimental findings on surface roughness indicate that FFF-printed PLA samples were significantly influenced by the layer thickness and raster angle, and an improvement in surface roughness is observed with the increase of nozzle temperature and reduction in feed rate. Microstructural SEM analysis was conducted to investigate the ruptured surfaces of the FFF printed PLA samples, focusing on the interlayer bonding quality and morphological characteristics including the effect of void formation, poor adhesion, and insufficient fusion between adjacent surface contact area with the effect of printing parameters. The feed rate and nozzle temperature were found to substantially influence the interlayer bonding between two adjacent surfaces.
