The two articles that follow appeared originally in MIT News.
Speed-modulated ironing enables makers to fabricate objects with varied colors and textures, like the owls pictured here, using only one material with high precision. The technique is faster and produces less waste than other methods. (Photo courtesy of the researchers)
New 3D Printing Technique Creates Unique Objects Quickly and With Less Waste
By using a 3D printer like an iron, researchers can precisely control the color, shade, and texture of fabricated objects, using only one material.
By Adam Zewe | MIT News
Multi-material 3D printing enables makers to fabricate customized devices with multiple colors and varied textures. But the process can be time-consuming and wasteful because existing 3D printers must switch between multiple nozzles, often discarding one material before they can start depositing another.
Researchers from MIT and Delft University of Technology have now introduced a more efficient, less wasteful, and higher-precision technique that leverages heat-responsive materials to print objects that have multiple colors, shades, and textures in one step.
Their method, called speed-modulated ironing, utilizes a dual-nozzle 3D printer. The first nozzle deposits a heat-responsive filament, and the second nozzle passes over the printed material to activate certain responses, such as changes in opacity or coarseness, using heat.
By controlling the speed of the second nozzle, the researchers can heat the material to specific temperatures, finely tuning the color, shade, and roughness of the heat-responsive filaments. Importantly, this method does not require any hardware modifications.
The researchers developed a model that predicts the amount of heat the “ironing” nozzle will transfer to the material based on its speed. They used this model as the foundation for a user interface that automatically generates printing instructions, which achieve color, shade, and texture specifications.
One could use speed-modulated ironing to create artistic effects by varying the color on a printed object. The technique could also produce textured handles that would be easier to grasp for individuals with weakness in their hands.
“Today, we have desktop printers that use a smart combination of a few inks to generate a range of shades and textures. 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,” said Mustafa Doğa Doğan, PhD ’24, co-author of a paper on speed-modulated ironing.
This project is a collaboration between the research groups of Zjenja Doubrovski, assistant professor at TU Delft, and Stefanie Mueller, the TIBCO Career Development Professor in the Department of Electrical Engineering and Computer Science (EECS) at MIT and a member of the MIT Computer Science and Artificial Intelligence Laboratory (CSAIL). Doğan worked closely with lead author Mehmet Ozdemir of TU Delft; Marwa AlAlawi, a mechanical engineering graduate student at MIT; and Jose Martinez Castro, of TU Delft. The research will be presented at the ACM Symposium on User Interface Software and Technology.
Modulating Speed to Control Temperature
The researchers launched the project to explore better ways to achieve multi-property 3D printing with a single material. The use of heat-responsive filaments was promising, but most existing methods use a single nozzle to do printing and heating. The printer always needs to first heat the nozzle to the desired target temperature before depositing the material.
However, heating and cooling the nozzle takes a long time, and there is a danger that the filament in the nozzle might degrade as it reaches higher temperatures.
To prevent these problems, the team developed an ironing technique where material is printed using one nozzle, then activated by a second, empty nozzle which only reheats it. Instead of adjusting the temperature to trigger the material response, the researchers keep the temperature of the second nozzle constant and vary the speed at which it moves over the printed material, slightly touching the top of the layer.
“As we modulate the speed, that allows the printed layer we are ironing to reach different temperatures. It is similar to what happens if you move your finger over a flame. If you move it quickly, you might not be burned, but if you drag it across the flame slowly, your finger will reach a higher temperature,” AlAlawi said.
The MIT team collaborated with the TU Delft researchers to develop the theoretical model that predicts how fast the second nozzle must move to heat the material to a specific temperature.
The model correlates a material’s output temperature with its heat-responsive properties to determine the exact nozzle speed which will achieve certain colors, shades, or textures in the printed object.
“There are a lot of inputs that can affect the results we get. We are modeling something that is very complicated, but we also want to make sure the results are fine-grained,” AlAlawi said.
The team dug into scientific literature to determine proper heat transfer coefficients for a set of unique materials, which they built into their model. They also had to contend with an array of unpredictable variables, such as heat that may be dissipated by fans and the air temperature in the room where the object is being printed.
They incorporated the model into a user-friendly interface that simplifies the scientific process, automatically translating the pixels in a maker’s 3D model into a set of machine instructions that control the speed at which the object is printed and ironed by the dual nozzles.
By modulating the speed of the second nozzle, which applies heat to a temperature-responsive filament, the researchers can vary the shade of materials to create objects with complex patterns, without the need to use multiple materials. (Photo courtesy of the researchers)
Speed-modulated ironing can be used to vary coarseness of heat-responsive materials in a fine-grained manner, enabling the fabrication of objects like this bike handle that has varied textures to improve a rider’s grip. (Photo courtesy of the researchers)
Faster, Finer Fabrication
They tested their approach with three heat-responsive filaments. The first, a foaming polymer with particles that expand as they are heated, yields different shades, translucencies, and textures. They also experimented with a filament filled with wood fibers and one with cork fibers, both of which can be charred to produce increasingly darker shades.
The researchers demonstrated how their method could produce objects like water bottles that are partially translucent. To make the water bottles, they ironed the foaming polymer at low speeds to create opaque regions and higher speeds to create translucent ones. They also utilized the foaming polymer to fabricate a bike handle with varied roughness to improve a rider’s grip.
Trying to produce similar objects using traditional multi-material 3D printing took far more time, sometimes adding hours to the printing process, and consumed more energy and material. In addition, speed-modulated ironing could produce fine-grained shade and texture gradients that other methods could not achieve.
In the future, the researchers want to experiment with other thermally responsive materials, such as plastics. They also hope to explore the use of speed-modulated ironing to modify the mechanical and acoustic properties of certain materials.
This article is reprinted with permission of MIT News (http://news.mit.edu/).
MIT Team Takes a Major Step Toward Fully 3D-Printed Active Electronics
By fabricating semiconductor-free logic gates, which can be used to perform computation, researchers hope to streamline the manufacture of electronics.
Adam Zewe | MIT News
Active electronics—components that can control electrical signals—usually contain semiconductor devices that receive, store, and process information. These components, which must be made in a clean room, require advanced fabrication technology that is not widely available outside a few specialized manufacturing centers.
During the Covid-19 pandemic, the lack of widespread semiconductor fabrication facilities was one cause of a worldwide electronics shortage, which drove up costs for consumers and had implications in everything from economic growth to national defense. The ability to 3D print an entire, active electronic device without the need for semiconductors could bring electronics fabrication to businesses, labs, and homes across the globe.
While this idea is still far off, MIT researchers have taken an important step in that direction by demonstrating fully 3D-printed resettable fuses, which are key components of active electronics that usually require semiconductors.
The researchers’ semiconductor-free devices, which they produced using standard 3D printing hardware and an inexpensive, biodegradable material, can perform the same switching functions as the semiconductor-based transistors used for processing operations in active electronics.
Although still far from achieving the performance of semiconductor transistors, the 3D-printed devices could be used for basic control operations like regulating the speed of an electric motor.
“This technology has real legs. While we cannot compete with silicon as a semiconductor, our idea is not to necessarily replace what is existing, but to push 3D printing technology into uncharted territory. In a nutshell, this is really about democratizing technology. This could allow anyone to create smart hardware far from traditional manufacturing centers,” said Luis Fernando Velásquez-García, a principal research scientist in MIT’s Microsystems Technology Laboratories (MTL) and senior author of a paper describing the devices, which appears in Virtual and Physical Prototyping.
He is joined on the paper by lead author Jorge Cañada, an electrical engineering and computer science graduate student.
An Unexpected Project
Semiconductors, including silicon, are materials with electrical properties that can be tailored by adding certain impurities. A silicon device can have conductive and insulating regions, depending on how it is engineered. These properties make silicon ideal for producing transistors, which are a basic building block of modern electronics.
However, the researchers didn’t set out to 3D-print semiconductor-free devices that could behave like silicon-based transistors.
This project grew out of another in which they were fabricating magnetic coils using extrusion printing, a process where the printer melts filament and squirts material through a nozzle, fabricating an object layer-by-layer.
They saw an interesting phenomenon in the material they were using, a polymer filament doped with copper nanoparticles.
If they passed a large amount of electric current into the material, it would exhibit a huge spike in resistance but would return to its original level shortly after the current flow stopped.
This property enables engineers to make transistors that can operate as switches, something that is typically only associated with silicon and other semiconductors. Transistors, which switch on and off to process binary data, are used to form logic gates which perform computation.
“We saw that this was something that could help take 3D printing hardware to the next level. It offers a clear way to provide some degree of ‘smart’ to an electronic device,” Velásquez-García said.
The researchers tried to replicate the same phenomenon with other 3D printing filaments, testing polymers doped with carbon, carbon nanotubes, and graphene. In the end, they could not find another printable material that could function as a resettable fuse.
They hypothesize that the copper particles in the material spread out when it is heated by the electric current, which causes a spike in resistance that comes back down when the material cools and the copper particles move closer together. They also think the polymer base of the material changes from crystalline to amorphous when heated, then returns to crystalline when cooled down—a phenomenon known as the polymeric positive temperature coefficient.
“For now, that is our best explanation, but that is not the full answer because that doesn’t explain why it only happened in this combination of materials. We need to do more research, but there is no doubt that this phenomenon is real,” he said.
3D-Printing Active Electronics
The team leveraged the phenomenon to print switches in a single step that could be used to form semiconductor-free logic gates.
The devices are made from thin, 3D-printed traces of the copper-doped polymer. They contain intersecting conductive regions that enable the researchers to regulate the resistance by controlling the voltage fed into the switch.
While the devices did not perform as well as silicon-based transistors, they could be used for simpler control and processing functions, such as turning a motor on and off. Their experiments showed that, even after 4,000 cycles of switching, the devices showed no signs of deterioration.
But there are limits to how small the researchers can make the switches, based on the physics of extrusion printing and the properties of the material. They could print devices that were a few hundred microns, but transistors in state-of-the-art electronics are only few nanometers in diameter.
“The reality is that there are many engineering situations that don’t require the best chips. At the end of the day, all you care about is whether your device can do the task. This technology is able to satisfy a constraint like that,” he said.
However, unlike semiconductor fabrication, their technique uses a biodegradable material, and the process uses less energy and produces less waste. The polymer filament could also be doped with other materials, like magnetic microparticles that could enable additional functionalities.
In the future, the researchers want to use this technology to print fully functional electronics. They are striving to fabricate a working magnetic motor using only extrusion 3D printing. They also want to finetune the process so they could build more complex circuits and see how far they can push the performance of these devices.
“This paper demonstrates that active electronic devices can be made using extruded polymeric conductive materials. This technology enables electronics to be built into 3D printed structures. An intriguing application is on-demand 3D printing of mechatronics on board spacecraft,” said Roger Howe, the William E. Ayer Professor of Engineering, Emeritus, at Stanford University, who was not involved with this work.
This work is funded, in part, by Empiriko Corporation.
This article is reprinted with permission of MIT News (http://news.mit.edu/).