Annealing of chopped and continuous fibre reinforced polyamide 6 produced by fused filament fabrication

Fused filament fabrication allows for the additive manufacturing of complex geometries without requiring moulds. The cooldown during the printing process causes the bonding between the layers to be weak. As a result, the mechanical properties are behind those of parts manufactured using conventional techniques. This study investigates the influence of an annealing process on the mechanical performance of continuous and chopped fibre reinforced polyamide 6 in the build-up direction. A correlation between the annealing temperature and the mechanical performance was found. The Young's modulus increased by a factor of three, while the ultimate tensile strength (UTS) increased by 50% for the chopped carbon fibre reinforced material and by 186% for the continuous glass fibre reinforced material. A temperature dependent transition from the gamma to the alpha phase was observed while the crystallinity only slightly changed. Air voids within the parts were found to be the main cause of embrittlement.