Five-axis material extrusion of high-performance structural parts with continuous carbon fiber-reinforced LM-PAEK

Utilizing continuous fiber-reinforced polymer composites in additive manufacturing (AM) enables end-use components with weight-specific mechanical performance that can surpass that of metals. In this paper, five-axis continuous fiber material extrusion (ME) was used to manufacture specimens from carbon fiber reinforced low-melt polyaryletherketone™ (LM-PAEK™) composite filaments. Mechanical testing revealed that the LM-PAEK matrix resolves typical challenges with high-performance thermoplastic polymers used in ME. Printed parts achieved an impressive short beam strength (SBS) of 60 MPa, flexural strength of 943 MPa, and inter-raster tensile strength of 62 MPa in curved regions. These samples also achieved a low void content and high crystallinity. Detailed thermal analysis via differential scanning calorimetry (DSC) showed that samples could achieve near-maximum crystallinity (∼25 %) in regions close to the heated print bed or after a brief post-annealing cycle (210 °C), underscoring the importance of spatial temperature control in ME. X-ray micro-computed tomography (μCT) confirmed a void content as low as 1.6 % for flat coupons, while systematic analysis of curved specimens quantified how steering radii below 10 mm induce fiber folding, wrinkling, and voids. A custom geometric bracket was fabricated to illustrate the capabilities of out-of-plane continuous fiber deposition and showcased similar defects due to tight curvatures as well as downward nozzle travel. Together, findings of this paper establish LM-PAEK as a promising matrix for continuous fiber AM and provide the first empirical design rules for fiber steering in multi-axis extrusion, advancing the field toward true load-bearing structural applications.