Identification of hybridization strategies for combining fused filament fabrication with unidirectional tape reinforcement

Additive manufacturing processes such as fused filament fabrication (FFF) enable highly individualized pro-duction with thermoplastics, can thus produce load-path-optimized components and therefore lightweight structures. Since the mechanical properties of FFF are lower than those of traditional processes, discontinuous and continuous fibers are used to improve the mechanical properties. Currently the reinforcement effect of continuous fibers cannot be fully utilized in FFF due to the lack of impregnation of the fibers and only low processing pressures during hybridization. To tackle this challenge, four strategies for hybridization of pre-impregnated unidirectional (UD) carbon fiber tapes with polyamide 6 (PA6) matrix and FFF-printed parts are investigated in this work. The strategies differ in the timing of the application of consolidation steps, i.e. a controlled application of heat and pressure in the interface between FFF-layers and UD-tape. With the use of mechanical pull-out tests, the maximum achievable shear stresses of the interface are investigated. Additional computed tomography (CT) scans of the interfaces allow the four hybridization strategies to be evaluated. It is shown that even a single consolidation in the right process step significantly increases the adhesion between UD-tape and FFF layer leading to about 100-200% increased shear stresses before delamination occurs. To ensure the transferability of the hybridization strategies to other material systems and to validate the results, filaments of pure PA6 as well as PA6 with short glass and carbon fibers were used for the FFF process.

Automated summary

Additive manufacturing processes like fused filament fabrication (FFF) allow for highly customized production and lightweight structures. However, the mechanical properties of FFF are lower, so the use of continuous fibers and consolidation steps are investigated to improve the properties. Four strategies for hybridization of pre-impregnated carbon fiber tapes with FFF-printed parts are studied and evaluated.