Continuous Carbon Fibers in 3D Printing
The development of composite materials, as well as the related improvement in design and in manufacturing technologies, is one of the most important advances in the history of materials [1]. Composites have unique advantages over monolithic materials, such as high strength, high stiffness, long fatigue life, low density, and adaptability to the intended function of the structure [2, 3].
A large number of composite manufacturing processes have been developed over the last 40 years and additive manufacturing is one of them. Additive Manufacturing (AM) is defined as a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to deploying subtractive manufacturing methodologies [4]. AM technologies offer the possibility of significant cost savings due to reduced material waste and the capability for tool-less production of intricate geometries. For this reason, especially in recent decades, they have gained popularity in line with the latest developments and market trends [5].
The main advantages of AM are its capacity for producing parts with high geometrical complexity at almost no added cost, short lead times, weight reduction and reduced effort required for assembly, and its suitability for customization, low volume production and even the manufacture of single parts. Moreover, some applications may need materials with unusual combinations of properties, which cannot be provided by metals, polymers or ceramics alone. For such applications, composite materials including two or more materials allow the combination of the required properties in a single material. Thus, AM, which can be defined as the production of objects directly from the CAD model through the process of adding materials in successive layers (as opposed to subtractive processes), is gaining significance in critical applications that make use of composite materials [6].
The Fused Filament Fabrication (FFF) process, which is also termed Fused Deposition Modeling (FDM), is the most widely-used 3D printing technology for two main reasons. Firstly, it employs inexpensive devices, and secondly it is easy to use when building complex parts with thermoplastic filaments, such as PLA, ABS, or nylon [5]. However, parts printed using thermoplastic filaments suffer from the major drawback of possessing poor mechanical properties, which restricts their applications. In recent years, researchers have enhanced the mechanical properties of thermoplastics by combining them with reinforced materials. Owing to its outstanding mechanical performance and lightweight characteristics, carbon fiber has acquired a crucial role in the field of composites. Short Carbon Fiber (SCF) is a noteworthy reinforced material because of the relatively simple procedure with which SCF-reinforced thermoplastics can be produced [7]. Short Carbon Fiber Reinforced Polymers (SCFRP) may improve mechanical properties, but these properties have been found to be only slightly better than those of pure plastic; they possess heightened porosity, and poor bonding has been detected because of the existence of SCF. The ideal solution for achieving significant improvement in strength is printing with Continuous Carbon Fibers (CCF) [7].
To improve the mechanical properties of a 3D printed part, it is vital to use a 3D printer that fabricates continuous carbon fiber-reinforced thermoplastics (CFRTP). A 3D printer that prints continuous CFRTP is able to reduce weight by optimizing the fiber direction in the components. This technology is well-suited for manufacturing a wide variety of products in small quantities. This could include the production of load-bearing orthopedic implants and artificial legs in the health-care sector or the manufacture of items for the automobile and aerospace industries [8].
In a very recent article, a method was presented for 3D printing of continuous fiber-reinforced thermoplastics based on fused-deposition modeling. The technique enables direct 3D fabrication without the use of molds and may become the standard next-generation composite fabrication methodology. A thermoplastic filament and continuous fibers were separately supplied to the 3D printer and, immediately before printing, the fibers were impregnated with the filament within the heated nozzle of the printer. Polylactic acid was used as the matrix while carbon fibers, or twisted yarns of natural jute fibers, were used as the reinforcements. The thermoplastics reinforced with unidirectional jute fibers were examples of plant-sourced composites; those reinforced with unidirectional carbon fiber displayed mechanical properties superior to those of both the jute-reinforced and unreinforced thermoplastics. Continuous fiber reinforcement was found to have improved the tensile strength of the printed composites relative to the values associated with conventional 3D-printed polymer-based composites [9].
The tensile modulus and strength of FDM-printed PLA composites are reported to be 19.5 ± 2.08 GPa and 185.2 ± 24.6 MPa respectively (see figure 1). These results indicate almost 6-fold and 4.5–fold enhancements in the tensile modulus and strength of the pure PLA specimens, improvements which are very pronounced compared to the properties of short fiber- reinforced PLA composites [9].
The approach of Kordsa to 3D Printing Applications and Directional Composites through the Manufacturing Innovation (DiCoMI) project
Although still in its early stages, composite 3D printing is gaining traction within the manufacturing industry. It provides a quick and automated approach to manufacturing composite parts, which used to be labor-intensive and which requires highly-skilled operators. The move to composite 3D printing calls for a re-evaluation of the choice of materials for some applications, replacing metals with equally strong and cheaper polymer composites. The tool-free fabrication technique for composites not only makes the process of fabricating composite parts much faster and less costly but also opens the possibility of multifunctional composite structures for new applications. These advantages are sure to lead 3D printing technology to be accepted as one of the standard techniques in the future composite maker’s toolkit [10].
With respect to the future of 3D printing applications in the composite industry, Kordsa aims to increase its know-how in this field by participating in a Horizon 2020 project, DiCoMI, a Marie Skłodowska-Curie Action (MSCA). Marie Skłodowska-Curie Actions support researchers at all stages of their careers, regardless of age and nationality. Researchers working across all disciplines are eligible for funding. MSCA also encourage cooperation between industry and academia and aim to promote innovative training to enhance employability and career development.
The Directional Composites through Manufacturing Innovation (DiCoMI) project aims to bring together leading innovators from across Europe and beyond, to develop a new method of producing composite material parts with optimized fiber directionality. The DiCoMI project will integrate advanced manufacturing techniques, composite materials science, and manufacturing system design. As such, it requires a high level of inter-disciplinary cooperation as well as collaboration between researchers and industry. The outcome will be a novel composite manufacturing system capable of producing low-cost parts with increased accuracy and enhanced functionality.
In the scope of the DiCoMI Project, in 2019 Kordsa organized two secondments, with Loughborough University (UK) and the Technical University of Cluj-Napoca (Romania). In January 2020, six researchers and two professors from Loughborough University, the Technical University of Cluj-Napoca and Kharkiv Aviation Institute (Ukraine) visited Kordsa and published research reports. Secondment to our project partners will continue and articles will be written as a consequence of the ensuing research.
REFERENCES
1. Kutz, M. (Ed.). (2015). Mechanical Engineers’ Handbook, Volume 1.: Materials and Engineering Mechanics. John Wiley & Sons.
2. Daniel, I. M., Ishai, O., Daniel, I. M., & Daniel, I. (1994). Engineering mechanics of composite materials (Vol. 3, pp. 256–256). New York: Oxford University Press.
3. Clyne, T. W., & Hull, D. (2019). An introduction to composite materials. Cambridge University Press.
4. Heidari-Rarani, M., Rafiee-Afarani, M., & Zahedi, A. M. (2019). Mechanical characterization of FDM 3D printing of continuous carbon fiber reinforced PLA composites. Composites Part B: Engineering, 175, 107147.
5. Brenken, B., Barocio, E., Favaloro, A., Kunc, V., & Pipes, R. B. (2018). Fused filament fabrication of fiber-reinforced polymers: A review. Additive Manufacturing, 21, 1–16.
6. Yasa, E., & Ersoy, K. A Review on the Additive Manufacturing of Fiber Reinforced Polymer Matrix Composites.
7. Hu, Q., Duan, Y., Zhang, H., Liu, D., Yan, B., & Peng, F. (2018). Manufacturing and 3D printing of continuous carbon fiber prepreg filament. Journal of Materials Science, 53(3), 1887–1898.
8. Omuro, R., Ueda, M., Matsuzaki, R., Todoroki, A., & Hirano, Y. (2017, August). Three-dimensional printing of continuous carbon fiber reinforced thermoplastics by in-nozzle impregnation with compaction roller. In 21st International conference on composite materials, Xian (pp. 20–25).
9. R. Matsuzaki, M. Ueda, M. Namiki, T.-K. Jeong, H. Asahara, K. Horiguchi, T. Nakamura, A. Todoroki, Y. Hirano. Three-dimensional printing of continuous-fiber composites by innozzle impregnation. Scientific Reports. 2016; 6.
10. Yeong, W. Y., & Goh, G. D. (2020). 3D Printing of Carbon Fiber Composite: The Future of Composite Industry? Matter, 2(6), 1361–1363.
Written by Koray Tansu İlhan,
Project Engineer, Composite Technologies, Kordsa
