Influence of fused filament fabrication process parameters on the quasi-static mechanical behaviour and failure mechanisms of 316L stainless steel

The emergence of fused filament fabrication (FFF) for metal printing has introduced a cost-effective alternative to traditional fusion-based metal additive manufacturing methods. Nevertheless, the highly inhomogeneous material microstructures resulting from this manufacturing technology seriously compromise its structural integrity performance. This study comprehensively investigates the influence of six key printing parameters – nozzle temperature, bed temperature, print speed, layer thickness, infill pattern, and infill percentage – on the quasi-static mechanical performance and dimensional accuracy of a 316L stainless steel produced via FFF. 316L stainless steel was selected as the focus material due to its widespread industrial relevance and early availability in filament form. A structured design of experiments (DOE) was implemented, followed by analysis of variance (ANOVA) and signal-to-noise (S/N) ratio analysis to assess both performance and consistency. Six material responses were evaluated: yield strength, ultimate tensile strength, stress and strain at break, toughness, and dimensional accuracy. Bed temperature was the most influential parameter, with the highest temperature of 120 °C enhancing interlayer bonding and thereby improving static mechanical properties and dimensional accuracy. The highest nozzle temperature of 250 °C provided moderate improvements in static mechanical performance, while increasing print speed to 40 mm/s improved deposition quality by reducing filament residence time and limiting binder degradation. Additionally, smaller layer thickness, line-based infill pattern, and full (100 %) infill further improved static mechanical properties by minimising interlayer voids and promoting efficient stress transfer. Hardness testing was performed to provide additional insight into the material's mechanical response. Alongside, fractography and porosity analysis were carried out to characterise failure mechanisms and quantify internal defects, revealing that large printing-induced pores dominate failure and persist after sintering, directly influencing mechanical reliability. These findings provide insights into parameter-dependent trends and interlayer bonding quality, contributing to the optimisation of print conditions for enhanced mechanical reliability and reduced variability in metal FFF components.