Novel Processes for the Production of Continuous Carbon Fiber-Reinforced Thermoplastic Polymers via Additive Manufacturing and Comparisons

Continuous fiber-reinforced polymer (CoFRP) parts offer significant potential
for reducing future product consumption and CO2 emissions due to their high tensile
properties and low density. Additive manufacturing enables the tool-free production of
complex geometries with optimal material utilization, making it a promising approach
for creating load-path-optimized CoFRP parts. Recent advancements have integrated
continuous fibers into laser sintering processes, allowing for the support-free production of
complex parts with improved material properties. However, additive manufacturing faces
challenges such as long production times, small component dimensions, and defects like
high void content. New processes, including Arburg Polymer Freeforming (APF), robotic
direct extrusion (DES) and the integration of thermoplastic tapes, and laser sintering, have
enabled the production of CoFRPs to address these issues. A comparison of these new
processes with existing material extrusion methods is necessary to determine the most
suitable approach for specific tasks. The fulfillment factor is used to compare composites
with different matrix and fiber materials, representing the percentage of experimentally
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achieved material properties relative to the theoretical maximum according to the Voigt
model. The fulfillment factor varies significantly across different processes and materials.
For FFF processes, the fulfillment factor ranges from 20% to 77% for stiffness and 14%
to 84% for strength, with an average of 52% and 37%, respectively. APF shows a high
fulfillment factor for stiffness (94%) but is lower for strength (23%), attributed to poor
fiber–matrix bonding and process-induced pores. The new DES process improves the
fulfillment factor due to additional consolidation steps, achieving above-average values for
strength (67%). The CoFRP produced by the novel LS process also shows a high fulfillment
factor for stiffness (85%) and an average fulfillment factor for strength (39%), influenced by
suboptimal process parameters and defects.