Researchers from the Massachusetts Institute of Technology (MIT) and Delft University of Technology have developed a new single-material, multi-property 3D printing process.
This technique is reportedly faster than other methods and produces 10 times less waste than existing multi-material systems such as the Bambu Lab X1-Carbon. Significantly, it does not require 3D printing hardware changes, potentially allowing any multi-nozzle 3D printer to unlock the capability.
The team’s new Speed-Modulated Ironing method combines a dual-nozzle FDM 3D printer with a heat-responsive material. It can produce multiple shades, textures, and shapes in a single print job without purging filament or switching between spools.
The first nozzle deposits the thermo-responsive filament at a low temperature, before the second nozzle ‘irons’ the material layer. By changing the speed of the second nozzle, the researchers were able to heat the extruded filament to specific temperatures. This process modifies the shade and texture of the material, enabling the creation of intricate patterns and images.
Speed-modulated ironing allows text, photos, and QR codes to be added to the surface of 3D printed objects, while surface coarseness can be amended to improve the tactility of parts. A digital tool was also created to automatically generate 3D printing instructions for the user’s color, shade, and texture specifications.
“Today, we have desktop printers that use a smart combination of a few inks to generate a range of shades and textures,” commented research co-author Mustafa Doğa Doğan. “We want to be able to do the same thing with a 3D printer – use a limited set of materials to create a much more diverse set of characteristics for 3D printed objects.”
The team hopes this new process will facilitate a “step software” to a more “versatile, expressive, and sustainable form of 3D printing.”
The study is titled: ‘Speed-Modulated Ironing: High-Resolution Shade and Texture Gradients in Single-Material 3D Printing.’ Its findings will be presented at the Association for Computing Machinery (ASM) Symposium on User Interface Software and Technology from October 13 – 16.
Multi-color 3D printing with a single material
Most multi-color 3D printers use multiple materials, either switching between tool heads or extruding different materials through the same nozzle. These processes are generally slow and inefficient.
In the latter, the nozzle must be heated to the desired temperature before extruding material. This time-consuming process can cause the material to degrade when reaching higher temperatures. It also wastes substantial material as filament must be purged before the next material is 3D printed.
To overcome these challenges, the MIT and Delft team developed their novel ironing technique. One nozzle 3D prints the temperature-sensitive material, which is then heated and activated by an empty nozzle.
The temperature of the second nozzle remains constant. It passes over the 3D printed layer at different speeds, exposing it to varying levels of heat. These variations are key to achieving the desired properties and shades.
Marwa AlAlawi, a mechanical engineering graduate student at MIT who worked on the study, compares this process to moving your finger over a flame. “If you move it quickly, you might not be burned,” he explained. “But if you drag it across the flame slowly, your finger will reach a higher temperature.”
To determine the nozzle speed required to achieve specific temperatures, the researchers developed a theoretical model which correlates the material’s heat-responsive properties with its output temperature. This combination allowed the team to determine the specific nozzle speeds needed to produce certain colors, shades, and surface textures.
The model has been incorporated into a user-friendly tool that can convert images, shades, patterns, and texture requirements into 3D printable G-code.
High-speed and low-waste 3D printing
The researchers tested their speed-modulated ironing technique using three different heat-responsive materials: a foaming polymer (LW-PLA), a PLA filament filled with wood fibers, and another filled with cork fibers.
LW-PLA features a foaming agent that converts the filament into a closed-cell structure when heated. These cells expand as more heat is applied, scattering light which creates bright colors and increases opacity. The other wood- and cork-filled filaments exhibit a progressively darker colored shade when exposed to heat, caused by pyrolysis.
During their experimentation, the researchers used the method to 3D print a range of objects including a photograph-emblazoned cup, shaded sculptures, and partially translucent water bottles.
When making the latter, the team ironed some LW-PLA layers at low speed to make opaque surfaces and ironed other regions at high speeds to make them translucent. A 3D printed bike handle was also produced with varied roughness to improve grip.
3D printing these parts on conventional multi-material 3D printers was found to be much less efficient. Speed-modulated ironing unlocked faster 3D print times and reduced material usage.
For instance, a cup featuring an image of Einstein took just 2h 30m to fabricate using the researcher’s method. 3D printing the same object on a Bambu Lab X1-Carbon, which purges material when switching filament, reportedly took 14h 30m. It also used over ten times the amount of material.
Developments in multi-color 3D printing
Efforts to optimize multi-color 3D printing are gaining traction within universities and research institutions. Indeed, the MIT-Delft team is not the first to explore multi-color 3D printing with a single material.
Earlier this year, researchers from the University of Illinois Urbana-Champaign and the Beckman Institute for Advanced Science and Technology developed a multi-color 3D printing process that uses a single ink, offering a more efficient and sustainable alternative to existing methods.
The process drew inspiration from color-changing chameleons and leveraged a UV-assisted ink-writing that allows structural colors to be changed “on the fly” during 3D printing. These colors were successfully programmed to reflect a wide spectrum of visible light. This included a recreation of Vincent Van Gogh’s “Starry Night” painting and a multi-colored 3D printed chameleon.
Elsewhere, scientists from the Eindhoven University of Technology (TUE) previously developed a direct ink writing (DIW)-compatible color-changing liquid crystal ink. This novel material was Inspired by naturally occurring iridescent materials that change color based on the angle from which they are viewed.
The material featured reflective qualities that are determined by the helical alignment of its molecules. This can be controlled during 3D printing by varying parameters such as 3D print speed. Ultimately, the TUE team argued that this multi-color 3D printing approach is valuable for applications such as decorative lighting, soft wearable sensors for health monitoring, and augmented reality optics.
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Featured image shows water bottles 3D printed using speed-modulated ironing. Photo via Photo via MIT and Delft University of Technology.
