Fused granulate fabrication of short glass fiber-reinforced PA6: Influence of printing parameters on mechanical performance, porosity, and fiber alignment

• First demonstration of processing a conventional injection molding-grade PA6GF30 on a commercial small-scale FGF 3D printer. • Systematic investigation of printing parameters (nozzle diameter, bead ratio, and velocity) on mechanical performance, porosity, and fiber alignment. • Fiber alignment behavior comparable to FFF, tunable through nozzle diameter adjustment. • Mechanical properties close to injection molding values achieved through optimized FGF processing. • Comparative analysis shows superior mechanical performance versus FFF-printed sFRPCs, including short carbon fiber-reinforced systems. Additive manufacturing (AM) via material extrusion (MEX), particularly fused granulate fabrication (FGF), enables the direct processing of injection-molding-grade pellet feedstock for 3D printing. In this study, the high-performance engineering composite polyamide 6 reinforced with 30 wt% short glass fibers (PA6GF30) was investigated using FGF on a small-scale, commercially available printer, representing a practical pathway toward industrial adoption. A full factorial design of experiments (DOE) was conducted to assess the influence of key printing parameters – nozzle diameter, bead ratio (layer height/nozzle diameter), and printing velocity – on the volumetric flow of the extruded material and its effects on mechanical properties, porosity and fiber alignment. Statistical analysis revealed that decreasing the volumetric flow resulted in higher fiber alignment, lower porosity and enhanced mechanical properties. With optimized printing parameters, the tensile modulus reached 9 GPa and the ultimate tensile strength 139 MPa, compared to 9.5 GPa and 170 MPa for injection-molded PA6GF30. The flexural modulus and strength achieved 7.3 GPa and 211 MPa, respectively. This study highlights the unique combination of an industrially relevant injection-molding-grade material and a commercially available FGF system, demonstrating that parts produced using screw-based FGF processes can achieve high structural integrity and mechanical performance comparable to injection-molded parts.