Fused deposition modeling (FDM), often simply referred to as 3D Printing, has been hailed as the future of manufacturing. However, the bad mechanical performance of parts produced by FDM compared to conventionally manufactured objects has limited its use to prototyping. Therefore, despite its promise of mass customization, FDM 3D Printing has not been adopted by industry for production. Researchers at ETH Zürich have developed a bioinspired approach to 3D print recyclable materials using cheap desktop printers that outperform state-of-the-art printed polymers and rival the highest performance lightweight materials. This will finally enable the manufacturing of complex parts that mimic natural structural designs on the mass market. 3D Printing, particularly FDM, makes it possible to produce unique complex parts quickly and at a low cost by sequentially depositing beads of a molten polymer. However, the available polymers are relatively weak and the printed parts show poor adhesion between the printed lines. Because of these limitations FDM has not yet been successfully implemented in commercial products. Traditionally, people increased the performance of polymers by including strong and stiff fibres such as glass or carbon fibres into the material. Although the resulting materials exhibit very high strength and stiffness, the energy- and labour-intensive fabrication process as well as the difficulty to recycle state-of-the-art composites represent major challenges today. For more information see the IDTechEx report on 3D Printing Materials 2018-2028.
To combine the mechanical properties of fibre-reinforced composites with the freedom in design that comes with 3D printing, methods have been developed to include carbon fibres into the printed objects. However, this approach requires expensive specialised equipment, and still is restricted with the possible geometries with materials that cannot be recycled. For the first time, researchers from the Complex Materials group and the Soft Materials group at ETH, were able to print objects from a single recyclable material with mechanical properties that surpass all other available printable polymers and can compete even with fibre-reinforced composites.
The researchers were inspired by two materials that can be found in Nature - spider silk and wood - during the development of these structures. Spider silk gets its unrivalled mechanical properties from the high degree of molecular alignment of the silk proteins along the fibre directions. First, it was possible to reproduce this high alignment during the extrusion from an FDM nozzle by using a liquid crystal polymer (LCP) as an FDM feedstock material, resulting in unprecedented mechanical properties in the deposition direction. Second, the anisotropic fibre properties were utilised by tailoring the local orientation of the print path according to the specific loading conditions imposed by the environment. This design principle is inspired by the ability of living tissue like wood to arrange fibres along the stress lines developed throughout the loaded structure (illustrated in Figure 1) as it grows and adapts to its environment.
The recyclable 3D printed LCP structures are much stronger than the state-of-the-art 3D printed polymers and do not require the labour- and energy-intensive steps involved in current composite manufacturing technologies. Thus, the technology is expected to be a game-changerin several structural, biomedical and energy-harvesting applications where high-performance lightweight materials are required. Additionally, because the research has been conducted using a readily available polymer and a commercial desktop printer, it should be easy for the broader additive manufacturing and open source communities to adopt this new material and digitally design and fabricate strong and complex lightweight objects from LCPs.
Source and top image: ETH Zurich