In ‘Grayscale digital light processing 3D printing for highly functionally graded materials,’ Chinese researchers make it clear that 3D printing has a long way to go for producing excellence in parts without significant investment and engineering. In looking toward biological structures, the authors suggest that functionally graded materials (FGMs) can improve mechanical properties of 3D printed objects. In assessing previous studies, they also settled on DLP 3D printing as the most promising method—especially for creating multi-material parts.
In this study, the researchers explain how they created a new 3D printing ink, used in grayscale printing with the single-vat grayscale DLP (g-DLP). The ink is meant to serve as the material for fabrication of highly tunable property gradients. Cured with grayscale light patterns that form the 3D printed structure, the object is cured a second time to ‘eliminate most of the residual monomers’ and improve mechanical properties. Ultimately, the researchers discovered that ‘broadly tailored functional gradients’ could be made, as they created lattice structures and different metamaterials.
A hybrid ink was created, and the researchers used a two-stage curing mechanism to refine the parts, with GMA monomers and diamine cross-linkers responsible for the thermal curing process. They examined the impact of grayscale on photopolymerization of the ink. Looking back at previous processes, the research team realized that two-stage curing systems usually produced uniform polymer networks or phase-separation structures. With their new method, the network was creating with both tunable density and chain architecture—without toxins, meaning that it is safe for many different applications.
“The differences in the network architecture and cross-linking density of the materials lead to widely tunable mechanical and thermomechanical properties. We first evaluated the mechanical properties of the printed materials,” stated the researchers. “The samples were printed using a single grayscale light for the first-stage curing. With only the first stage photocuring, the Young’s modulus spans only a few times from 1.5 to 8.1 MPa when the grayscale varies from G80 to G0, which is not enough for broader applications.
Continuing to show the potential of g-DLP printing, the researchers also printed simple geometrical shapes with gradients, along with further exploring 3D printing lattices and bioprinted structures which displayed high resolution and ‘clean appearance.’ They also found that these printed structures deformed suitably for applications like energy absorption, bordering on the 4D realm as shape memory polymers, envisioning use in future applications like:
- Voxel printing
- 4D printing for metamaterials
- Presurgical model planning
- Soft robotics
- Additive manufacturing with cyber security
“Although our approach enables significant advantages, there are still several issues that need to be addressed for its wide applications. First, the actual resolution of properties for the g-DLP should be determined. Besides the printer device itself, the voxel resolution for g-DLP in the x-y plane and z axis can be affected by both the resin and the printing parameters. Moreover, the grayscale value of the pixel would also have an influence on the voxel resolution. Second, the relationship between the curing condition, molecular structures, and mechanical properties of the grayscale cured samples needs to be further understood,” concluded the authors. “The nanoscale mechanical test and modeling approaches would provide an attractive pathway to this end, which is part of the ongoing work.”
“Last, when grayscale is used, polymers are cured to different degrees, which results in a slight difference in printed size. However, this can be fixed by software. For example, the projecting area with larger grayscale can be adjusted larger to compensate for the difference.”
Improving mechanical properties in 3D printing is a challenge that many users have taken on lately as they hope to make stronger, more functional parts whether in scaling up nanotechnology, formulating inks and resins, or studying how other factors affect strength and durability. Find out more about how mechanical properties affect 3D printed parts and how they can be improved here. What do you think of this news? Let us know your thoughts! Join the discussion of this and other 3D printing topics at 3DPrintBoard.com.