Researchers at Northwestern University have developed a hybrid additive manufacturing process called direct ink additive lithography (DIAL) that prints thick, particle-filled extrusion inks at speeds and resolutions closer to those of light-based printing. The work, led by Pranav Kaarthik, was published in Science Advances.
The method targets a longstanding trade-off. Digital light processing requires low-viscosity, weakly scattering resins, while direct ink writing can handle functional yield-stress inks but is slowed by filament-by-filament deposition and limited by nozzle diameter. "In 3D printing, manufacturers have had to choose between the materials they need and the printing speed, resolution, and scale they want," said Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern University. "With DIAL, we lay a foundation for eliminating that compromise."
How the process works
For each layer, a slot die extrudes ink onto the substrate and a doctor blade scrapes the deposit into a sheet as thin as 25 microns. A 405-nanometer projector then travels over the sheet and crosslinks selected regions, leaving uncured ink in place to serve as support. Because light only has to pass through a thin sheet rather than a deep volume of material, opaque, heavily filled inks remain printable. The projector's 50-micron pixel pitch sets the planar resolution.
Printed demonstrations
Using a model ink of polyurethane-based resin thickened with fumed silica, the team printed a 60 mm by 40 mm log pile structure in 30 minutes, compared with 124 minutes for direct ink writing, along with fins about 150 microns thick. Rastering the projection across overlaid ink sheets produced a multimaterial lattice four times the projector's illumination area.
The researchers also reported:
- Interlocking chain mail with struts roughly 250 microns thick;
- 15 gyroid structural electrolyte lattices printed from an ionogel ink in a single 15-minute run;
- Hydrogel cell culture inserts containing 0.5-mm-deep inverted pyramids.
Scaling outlook
The authors described their reported print times as conservative, noting that tool changes had not been tuned for speed. They added that the absence of the suction and peel forces found in vat-based printing should make it easier to expand build area and volume.
"Rebuilding American manufacturing will depend on new ways to make advanced materials," Truby said. "Because DIAL can print many complex, functional parts at once, we see a path toward scaling it from the lab to larger-volume manufacturing of architected materials for applications spanning robotics, aerospace, healthcare, and much more."
Kaarthik and Truby are listed as coinventors on a U.S. provisional patent application. Funding came from the National Science Foundation, the Air Force Office of Scientific Research and Northwestern's McCormick School of Engineering.