Researchers at Northwestern University have developed a hybrid additive manufacturing method aimed at removing a long-standing trade-off in 3D printing: choosing between high-performance materials and fast, fine-resolution production. Called direct ink additive lithography (DIAL), the process is described in Science Advances in work led by Pranav Kaarthik.
Each of the two established routes carries its own constraint. Digital light processing requires low-viscosity resins that scatter light only weakly, which rules out many particle-filled formulations. Direct ink writing can handle functional yield-stress inks, but filament-by-filament deposition is slow and feature size is limited by nozzle diameter.
How the process works
DIAL combines the two. 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 only the selected regions, leaving uncured ink in place to act as support. Because light only has to pass through a thin sheet, opaque and heavily filled inks remain printable. Planar resolution is set by the projector's 50-micron pixel pitch.
"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. "With DIAL, we lay a foundation for eliminating that compromise."
Demonstrated results
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, against 124 minutes with direct ink writing, and produced fins about 150 microns thick. Rastering the projection across overlaid ink sheets yielded a multimaterial lattice covering four times the projector's illumination area.
The group also printed interlocking chain mail with struts roughly 250 microns thick, 15 gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run, and hydrogel cell culture inserts containing 0.5-mm-deep inverted pyramids.
The authors describe their reported print times as conservative, noting that tool changes had not been tuned for speed. They add that the absence of the suction and peel forces typical of 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.