Influence of energy density on selective laser sintering of carbon fiber-reinforced PA12

This work provides an in-depth investigation of the influence of laser energy density on the mechanical, surface, and dimensional properties of carbon fiber-reinforced PA12 parts manufactured by selective laser sintering (SLS). A space-filling design of experiments (DOE) was used to conduct the experimental trials to cover a wide range of laser sintering parameters. The consolidation mechanism was evaluated by microstructural and crystallization evolution of the samples produced at different energy densities, supported by mechanical testing, scanning electron microscopy (SEM), X-ray diffraction (XRD), and infrared spectroscopy (FTIR). Surface morphology was evaluated by profile measurements and SEM images. Laser sintering parameters had a significant influence on physical and mechanical properties, exhibiting complex and nonlinear behavior. Low energy density resulted in better dimensional accuracy, whereas intermediate laser energy resulted in the best mechanical properties. A trade-off could be seen when mechanical or dimensional properties were desired, and optimum energy values were strongly dependent on the criteria desired. All samples exhibited a brittle fracture behavior, with little plastic deformation present. Fracture mechanism occurred in the interlayer region or interface between carbon fiber and PA12, depending on the energy density applied. XRD analysis revealed a decrease in crystal fraction with increasing energy density. FTIR measurement suggested that polymer degradation at high energy densities could be present by both polymer chain scission and oxygen functional group decomposition and gas release upon laser heating of carbon fiber, resulting in lower mechanical properties.