Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography, or DIAL, that is designed to print thick, particle-filled extrusion inks at speeds and resolutions closer to light-based processes. The work, led by Pranav Kaarthik, was published in Science Advances.
The method addresses a trade-off between digital light processing and direct ink writing. DLP requires low-viscosity, weakly scattering resins, while DIW can handle functional yield-stress inks but is slowed by filament deposition and limited by nozzle diameter. According to the team, DIAL is intended to reduce that compromise between the materials manufacturers need and the speed, resolution and scale they want. Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern, said the process lays a foundation for eliminating that trade-off.
In DIAL, each layer begins with a slot die extruding ink onto a substrate. A doctor blade then scrapes the deposit into a sheet as thin as 25 microns. A 405-nanometer projector travels over the sheet and crosslinks selected regions, leaving uncured ink in place as support. Because light passes only through a thin sheet, opaque and heavily filled inks remain printable, the researchers report. The projector's 50-micron pixel pitch sets the planar resolution.
Demonstrations and reported speeds
Using a model ink made from a polyurethane-based resin thickened with fumed silica, the team printed a 60 mm by 40 mm log pile structure in 30 minutes. The same structure took 124 minutes with DIW, according to the paper. The team also produced fins about 150 microns thick. Rastered projection over overlaid ink sheets yielded a multimaterial lattice four times the projector's illumination area.
Other demonstrations included interlocking chain mail with struts about 250 microns thick, 15 gyroid structural electrolyte lattices printed from an ionogel ink in a single 15-minute run, and hydrogel cell culture inserts containing 0.5-mm-deep inverted pyramids. The authors described their print times as conservative because tool changes had not been tuned for speed. They also said the absence of suction and peel forces seen in vat-based printing should make it easier to expand build area and volume.
The researchers see potential for DIAL in producing many complex, functional parts at once. Truby said rebuilding American manufacturing will depend on new ways to make advanced materials, and that DIAL offers a path toward scaling from the lab to larger-volume manufacturing of architected materials for robotics, aerospace, healthcare and other applications. 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.