Researchers at Northwestern University have developed a hybrid 3D printing method called direct ink additive lithography (DIAL) to print thick, particle-filled inks at speeds and resolutions closer to those of light-based processes. The work, led by Pranav Kaarthik, was published in Science Advances.
DIAL is intended to bridge two common approaches. Digital light processing requires low-viscosity, weakly scattering resins, while direct ink writing can handle functional yield-stress inks but is slowed by filament deposition and limited by nozzle diameter.
How the process works
For each layer, a slot die extrudes ink onto a substrate, and a doctor blade scrapes it into a sheet as thin as 25 microns. A 405-nanometer projector then moves over the sheet and crosslinks selected regions. Uncured ink remains in place as support. Because light has to pass only through a thin sheet, opaque, heavily filled inks remain printable. The projector's 50-micron pixel pitch sets the planar resolution.
Ryan Truby, the 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 is meant to lay a foundation for removing that compromise.
Printed parts 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, compared with 124 minutes using direct ink writing. 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.
The researchers printed interlocking chain mail with struts about 250 microns thick and 15 gyroid structural electrolyte lattices from an ionogel ink in a single 15-minute run. They also made 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.
Scale-up considerations
The authors said the absence of suction and peel forces seen in vat-based printing should ease expansion of build area and volume. Truby said 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 it 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.