If you own or have ever used a 3D printer, you know how long printing objects with a single material can take. If you have a printer that’s capable of printing multiple materials in the same print, you know that printing time increases exponentially with every material change. Toss in color changes too and a print that once took just a few hours to complete might now take a day or more to complete. Thankfully, a good amount of funding has been spent on research into multi-material 3D printing and the results have been very promising.
Take, for example, a recently published paper from Harvard’s Wyss Institute for Biologically Inspired Engineering and the John A. Paulson School of Engineering and Applied Sciences (SEAS) that details a new multi-material multi-nozzle method of 3D printing (abbreviated MM3D) that allows material changes up to 50-times per second, per nozzle. Each nozzle can switch between 8 separate materials at this rate, making complex, multi-material prints much faster. The increase in speed is so significant, that under the right circumstances, a print’s time to complete could be reduced by 90% or more.
The printhead can accommodate multiple nozzles, each of which can print up to eight different materials. A series of branched channels distribute the “inks” to the nozzles. Credit: Lori K. Sanders
This is possible as each printhead is itself 3D printed, and contains a series of channels and junctions that split an ink-like material into several paths leading to a nozzle. Each material is fed to each nozzle in this manner. The material flow is controlled by high-speed pressure valves that are capable of switching on and off up to 50-times per second. Since there is nothing to heat up, as would be the case in an FDM style printer, the material can flow quickly out of the array of nozzles on the bottom of the print head.
“When printing an object using a conventional extrusion-based 3D printer, the time required to print it scales cubically with the length of the object, because the printing nozzle has to move in three dimensions rather than just one,” said co-first author Mark Skylar-Scott, Ph.D., a Research Associate at the Wyss Institute. “MM3D’s combination of multinozzle arrays with the ability to switch between multiple inks rapidly effectively eliminates the time lost to switching printheads and helps get the scaling law down from cubic to linear, so you can print multimaterial, periodic 3D objects much more quickly.”
Since the print heads are themselves 3D printed, the channels that deliver the material to the nozzle can be fine-tuned to deliver different viscosity materials at very precise rates. This could come in handy when a print requires a flexible material to be printed alongside a rigid material, or say if two different resins, one conductive, one nonconductive needed to be printed together. The more viscous conductive resin could be delivered to the nozzle via a larger channel allowing the same amount of flow as a less viscous resin that’s being printed on each side of it. These materials could be printed from the same nozzle even as the print head’s design works in conjunction with the high-speed valves to maintain a positive pressure in each material feed tube. This prevents the materials from mixing by backflowing up another tube.
“Because MM3D printing can produce objects so quickly, one can use reactive materials whose properties change over time, such as epoxies, silicones, polyurethanes, or bio-inks,” said co-first author Jochen Mueller, Ph.D., a Research Fellow at the Wyss Institute and SEAS. “One can also readily integrate materials with disparate properties to create origami-like architectures or soft robots that contain both stiff and flexible elements.”
The team of researchers demonstrated this new MM3D technique by Miura origami structure composed of stiff “panel” sections connected by highly flexible “hinge” sections. The printhead used eight nozzles that alternated printing two different epoxies, one stiff and one very flexible once cured. The structure was printed as one solid piece, where in the past it would have been constructed of several different printed pieces that were mechanically glued together. The structure was folded over 1000 times before one of the flexible hinges experienced a failure.
Another example that the team showcased was a multi-material millipede-like creature that utilized stiff and soft materials with internal air passageways that would allow the soft-robot to walk when a vacuum was applied to the passageways. “This method enables the rapid design and fabrication of voxelated matter, which is an emerging paradigm in our field,” said corresponding author Jennifer A. Lewis, Sc.D., who is a Core Faculty Member at the Wyss Institute and the Hansjörg Wyss Professor of Biologically Inspired Engineering at SEAS. “Using our broad palette of functional, structural, and biological inks, disparate materials can now be seamlessly integrated into 3D-printed objects on-demand.”