Testing the printability of 3D inks

Three-dimensional printing can produce objects with complicated geometries, which may be difficult to form with traditional manufacturing, and can enable rapid prototyping by changing material composition and final structure.

Direct ink writing, a type of 3D printing, extrudes a paste-like ink from a nozzle, which is cured to produce a solid, stable, printed part. Rheology dictates how the printing material deforms and holds its shape.

To facilitate more informed ink development and save researchers time and resources, Cipriani et al. explored the rheological behavior of inks, or their printability.

“Currently, inks for direct ink writing are developed through guess-and-check methods,” said author Chandler Benjamin. “Inks are optimized for printability first, then rheology is evaluated.”

Using a mechanical mixer, the team combined a liquid photopolymer resin with solid, spherical beads of paraffin wax to create a thicker, homogeneous suspension. The resin is a honey-like Newtonian fluid, so it flows like a liquid. Meanwhile, the wax is viscoelastic, and adding it viscosifies the mixture.

The authors examined the wax loading in the ink and found that printing worked between 43 and 73 volume percent.

“A better understanding of ink rheology will help to optimize ink printability and standardize ink development over a variety of materials,” said Benjamin. “The field is rapidly evolving, and the techniques we use can help researchers deepen their understanding of their own inks, as well as their relationship to those that others use.”

In the future, the group plans to continue developing inks to understand the commonality of rheological properties across different compositions.

Source: “Viscoelastic and thixotropic characterization of paraffin/photopolymer composites for extrusion-based printing,” by Ciera E Cipriani, Yalan Shu, Emily B. Pentzer, and Chandler C. Benjamin, Physics of Fluids (2022). The article can be accessed at https://doi.org/10.1063/5.0104157 .