Researchers at Northwestern University have developed a hybrid additive manufacturing process that aims to combine the material range of direct ink writing with the speed and resolution associated with light-based printing. The method, called direct ink additive lithography (DIAL), is described in a study published in Science Advances and led by Pranav Kaarthik.
The team frames DIAL as a response to a trade-off in existing processes. Digital light processing relies on low-viscosity, weakly scattering resins, while direct ink writing can handle functional yield-stress inks but is slowed by filament deposition and constrained by nozzle diameter. DIAL instead forms each layer as a thin sheet and uses projected light to solidify selected areas.
In the DIAL sequence, a slot die extrudes ink onto a substrate. A doctor blade then scrapes the deposit into a sheet that can be as thin as 25 microns. A 405-nanometer projector moves over the sheet and crosslinks chosen regions. Ink that is not exposed remains in place and acts as support during the build. Because light only passes through a thin sheet, the process can use opaque, heavily filled inks that would be difficult for vat-based light printing. Planar resolution is set by the projector's 50-micron pixel pitch.
Using a model ink made from a polyurethane-based resin thickened with fumed silica, the researchers printed a 60 mm by 40 mm log pile structure in 30 minutes. The same structure took 124 minutes with direct ink writing, according to the study. They also produced fins about 150 microns thick. By rastering projection over overlaid ink sheets, the team made a multimaterial lattice covering four times the projector's illumination area.
The paper reports several demonstrator parts: 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. These examples suggest the process can handle filled functional inks and architectures that combine fine features with multi-layer construction.
Ryan Truby, June and Donald Brewer Junior Professor of Materials Science and Engineering at Northwestern, said manufacturers have had to choose between the materials they need and the printing speed, resolution and scale they want. He said DIAL lays a foundation for eliminating that compromise. The authors also describe their reported print times as conservative because tool changes had not been tuned for speed. They add that the absence of suction and peel forces found in vat-based printing should make it easier to expand build area and volume.
Truby linked the work to broader manufacturing goals, saying that rebuilding American manufacturing will depend on new ways to make advanced materials. Because DIAL can print many complex, functional parts at once, the team sees a path toward scaling the method 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. The work received funding from the National Science Foundation, the Air Force Office of Scientific Research and Northwestern's McCormick School of Engineering.