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How can we create 3D printed carbon fiber polymer composites?

In a review recently published in the journal Additive manufacturingresearchers discussed additive manufacturing (AM) of carbon fiber reinforced high-density polymer composites.

Study: Additive manufacturing of high density carbon fiber reinforced polymer composites. Image Credit: William Potter/Shutterstock.com

Background

By using carbon fiber reinforced polymer (CFRP) composites, lightweight structures with excellent strength and stiffness can be achieved. Due to its advantages in AM, such as chemical resistance and melt processability, thermoplastics are becoming increasingly common.

In universities and companies, fiber-reinforced thermoplastics are attracting great interest. Currently, AM uses staple or short fibers more frequently than continuous fibers. AM can be processed using sheet rolling, powder bed fusion, material extrusion, stereolithography, and fiber-reinforced polymer composites.

There has been little research on composites although selective laser sintering (SLS) is one of the fastest growing AM techniques for metals and polymers, due to limited improvements in mechanical properties over time. detriment of the increase in the porosity of the components.

The most popular processes for producing fiber-reinforced thermoplastic components are those that rely on material extrusion, including fused filament fabrication (FFF). The limited supply of materials and the significant amount of porosity in the finished parts are just two of the many challenges facing the AM of composites. Research demonstrates that by reducing void content, post-curing FFF printed composites with a heat press can significantly improve their tensile and flex properties.

However, it is impractical to apply enough heat and pressure to maintain the geometry of FFF components. This method has not yet been used in an independent academic study to create components or study how different processing conditions affect final product attributes.

About the study

In this study, the authors discussed the selective printing of staple carbon fiber sheets with a binder and polymer powder using a technique called composite fiber additive manufacturing (CFAM), which was then compressed, heated and post-processed to create clean-shape components. . The results showed a relationship between the compaction pressure used and the volume percentage of fibers or porosity inside the components.

The team demonstrated a new method for the development of discontinuous carbon fiber reinforced polymer composite parts with a porosity of 1.5%, a tensile strength of 97 MPa, a fiber volume content of 15% and a modulus of elasticity of 8.9 GPa. The prepared carbon fiber reinforced polymer parts had better mechanical properties than state-of-the-art AM.

The researchers produced discontinuous CFRP composite parts at the University of Sheffield using CFAM, which was based on a sheet rolling method similar to composite-based additive manufacturing (CBAM). In order to understand the impacts of the quantity of ink printed and the pressure/duration of compaction on the density and the qualities of the final components, this study aimed to compare the performances of the composite parts created by CFAM for the first time with tests mechanical and X-ray tests. tomography.

Comments

The 223 gsm2 the parameter level offered stronger fibre-matrix adhesion than the 24 g/m2 of ink and a higher carbon fiber volume fraction (FVF) than 892 g/m2 of ink, making it the ideal setting level for the highest tensile strength and stiffness. It was found that 41.6, 208.3 and 291.6 grams of powder per m2 can be supported by 24, 223 and 892 g/m2 ink, respectively. The maximum elastic modulus, tensile strength, bending strength and modulus were provided by the highest pressure of 0.9 MPa. The second important aspect was the areal density of the printed ink. Ink was the best factor in the medium parameter, 223 g/m2, which had the most production. In this experiment, compaction time was found to be the least important variable. It has been discovered that Nylon 12 crystallizes between 160 and 165°C.

The CFAM method has been compared to the most advanced staple fiber AM techniques, and has been shown to have the ability to produce complex staple fiber reinforced polymer composite parts with superior strength, stiffness and density with a stiffness of 8.9 GPa, tensile strength of 97 MPa, and 1.5% porosity. The microstructural and mechanical qualities of the final CFAM parts were affected by the optimization of ink surface density, compaction time and pressure. The amount of polymer powder adhering to the substrate was significantly influenced by ink surface, while compaction time had the least effect.

Low ink concentration was found to increase the likelihood of interlayer delamination because there was insufficient bonding between the layers. The fiber volume fraction, however, decreased as the ink volume increased because there was more matrix material present. It was determined that the most important factor affecting the properties of the final part in terms of stiffness, strength and microstructural properties was the use of high pressure and temperature, which facilitated complete fusion nylon powder between the layers and reduced the resistance of the component. overall porosity.

conclusion

In conclusion, this study elucidated that the proposed method can also provide the versatility to process a variety of fibers such as glass textiles with varied mesh density and thermoplastic matrix materials such as PEEK powder.

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Source

Karaş, B., Smith, PJ, Fairclough, JPA, et al. Additive manufacturing of high density carbon fiber reinforced polymer composites. Additive Manufacturing 103044 (2022). https://www.sciencedirect.com/science/article/abs/pii/S2214860422004365

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