International researchers have created a novel framework for strengthening 3D prints by aligning filaments, detailing their study in the recently published “Reinforced FDM: Multi-Axis Filament Alignment with Controlled Anisotropic Strength.”
As has long been shown, anistropy is typically a weakness of 3D printing, particularly in fused deposition modeling processes. Due to the relative weakness of inter-layer bonding, the Z-axis is much weaker than the X and Y axes. In the case of this research, however, anisotropy is actually used to improve the strength of 3D printed objects by over two times. This is in contrast to more conventional methods typically used for strengthening parts such as modifying geometry, optimizing parameters like printing orientation or infill percentage and structure, or performing post-treatment processing via thermal or chemical features.
This research uses the new framework to take advantage of the anisotropy, creating “field-based optimization” for fabricating curved layers (and better control) for supporting structures. Using finite element analysis (FEA), fields were optimized for collision-free printing, and toolpaths generated on the curved layers to align filaments in the desired directions. Samples for the study were created on an FDM 3D printer.
In previous studies, anisotropy of mechanical properties has been used for strengthening models, with infill and microstructures being adapted also for better topology. Structural analyses have been performed to assess the best printing direction, while others have studied the proper orientation using FEA safety factors. Ultimately, however, most researchers have realized the limitations presented by the deposition of planar layers.
While the “computational pipeline” for this study was used to create curved layers and toolpaths as designated by principal stress distribution, the authors found that the biggest obstacle was to simultaneously optimize filament alignment while also dealing with manufacturing constraints. Previous research studies have attempted to employ multi-axis 3D printing; however, the results have shown limited success, and no application for mechanical anisotropy brought on due to “different toolpaths of filament alignment.”
A vector field was identified for “governing field’s gradients” and then scalar fields were able to be computed at the end. Using this approach, the team was able to take a nonlinear optimization issue and turn it into several linear optimization problems that could be easily fixed, with further algorithms written to allow access and thorough manipulation of layer thickness.
Designing toolpaths within a three-manifold also meant improving accessibility, support generation, layer thickness, and toolpath generation. Ultimately, these issues were solved by finding the best orientation with a new metric, allowing for field relaxation, and refining meshing, slicing, and trimming. Several samples were created, with all featuring the curved layers generated by the new computational framework.
One of the most concerning limitations of this technique was in the slower speed. While precision was improved, the researchers noted that the tradeoff was difficulty in achieving high speed and stable rotation motions. Along with that came another constraint:
“Our ray-based method to determine the overhang regions needs supporting structures, which may generate rays having no intersection with any prior layers or the platform. When this occurs, we apply some local perturbation to adjust a ray’s orientation until it can intersect with the platform,” explained the researchers. “This is another limitation of our approach. It is worthy to investigate a better method for the support generation. Using optimized design (e.g., [Dumas et al. 2014]) can significantly reduce the time and material used to fabricate the supporting structures.”
Overall though, the experiment was found to be “encouraging,” especially as models 3D printed with this method can hold up under loads exponentially higher than in planar-layer based FDM 3D printing.[Source / Images: “Reinforced FDM: Multi-Axis Filament Alignment with Controlled Anisotropic Strength”]
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