Development of improved fibre reinforced feedstocks for high performance 3D printing

Abstract

In the last ten years, much progress has been made combining the field of additive manufacturing (AM) and fibre composite materials. An AM technique such as Fused Filament Fabrication (FFF) allows rapid prototyping of complex parts at a low cost but lacks in mechanical properties to make them applicable as structural components. The addition of reinforcing fibres to thermoplastic filaments has been demonstrated to improve the mechanical properties of 3D printed parts. The fibre architecture plays an important role on the performance and processing of the filament, and in this work a new High Performance Discontinuous Fibre (HiPerDiF) filament is presented for an optimal trade-off between performance and processing.

Two existing fibre reinforced filaments for FFF were assessed: short fibre filament and continuous fibre filament. Short fibre filaments have fibres with a length of ~0.1 mm which provide little reinforcing effect but can be processed using a standard 3D printer. Continuous fibre filaments have an order of magnitude higher mechanical properties than short fibre filaments, but they are harder to deposit through corner radii due to the inextensibility of the carbon fibres resulting in a lower quality part.

Aligned discontinuous fibre reinforced composite (ADFRC) tapes were prepared with 3 mm carbon fibres using the HiPerDiF fibre alignment method invented at the University of Bristol. Suitable thermoplastic polymer matrix systems were chosen (PLA, ABS, PA, PETG) based on the FFF process requirements. A novel filament forming method has been developed that allows consolidated ADFRC tapes to be formed into a 3D printing filament via a direct extrusion method, utilizing the aligned fibre architecture for better flow behaviour. A thermal and rheological analysis was performed to improve the filament forming method and identify suitable processing windows. Short filament strands were prepared that enabled the first 3D printing trials with the HiPerDiF filament.

Performance-wise, the tensile strength and stiffness of the ADFRCs was an order of magnitude higher than available short fibre filament, and comparable to continuous fibre filaments. The processing of the HiPerDiF filament showed better deposition quality through corner radii than continuous fibre filament. This work has demonstrated the hypothesized benefits of aligned fibre reinforced composites for improved 3D printing feedstocks and further work has been identified to improve the filament manufacturing method and quality.

Date of Award	26 Nov 2020
Original language	English
Awarding Institution	University of Bristol
Supervisor	Ben K S Woods (Supervisor) & Marco L Longana (Supervisor)