By imitating ironing, researchers perfect 3D printing’s control over color, texture and hue

Multi-material 3D printing allows manufacturers to make custom devices with multiple, varied colors and textures. But the process can be time-consuming and wasteful, as existing 3D printers must switch between multiple nozzles, often rejecting one material before they can begin depositing another.

Researchers from MIT and Delft University of Technology have introduced a more efficient, lower cost, and higher precision technique that leverages heat-sensitive materials to print objects with multiple colors, shades, and textures in a single step.

Their method, called modulated speed ironing, uses a dual-nozzle 3D printer. The first nozzle deposits a heat-sensitive 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, researchers can heat the material to specific temperatures, precisely adjusting the color, hue and roughness of the heat-sensitive filaments. It is important to note that 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 basis for a user interface that automatically generates printing instructions that meet color, hue, and texture specifications.

Ironing at modulated speed could be used to create artistic effects by varying the color of a printed object. The technique could also produce textured handles that would be easier to grip for people with weakness in their hands.

“Today we have desktop printers that use a clever 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 more diverse set of characteristics for 3D printed objects,” says Mustafa Doğa Doğan Ph.D. ’24, co-author of an article on ironing at modulated speed.

This project is a collaboration between the research groups of Zjenja Doubrovski, assistant professor at TU Delft, and Stefanie Mueller, TIBCO Career Development Professor in the Department of Electrical Engineering and Computer Science (EECS) at MIT and member of MIT Computer Science. and Artificial Intelligence Laboratory (CSAIL).

Doğan worked closely with lead author Mehmet Ozdemir from TU Delft; Marwa AlAlawi, graduate student in mechanical engineering at MIT; and José Martinez Castro from TU Delft. The research will be presented at the ACM Symposium on User Interface Software and Technologies (UIST 2024) in Pittsburgh October 13-16.

Modulating speed to control temperature

The researchers launched the project to explore better ways to achieve multi-property 3D printing with a single material. Using heat-sensitive filaments showed promise, but most existing methods use a single nozzle to perform printing and heating. The printer should always first heat the nozzle to the desired target temperature before depositing the material.

However, heating and cooling the nozzle takes a long time and the nozzle filament may degrade when it reaches higher temperatures.

To avoid these problems, the team developed an ironing technique in which the material is printed using one nozzle, then activated by a second empty nozzle which only heats it. Instead of adjusting the temperature to trigger the material’s response, the researchers hold the temperature of the second nozzle constant and vary the speed at which it moves over the printed material, lightly touching the top of the layer.

“As we modulate the speed, it allows the printed layer that we are ironing to reach different temperatures. It’s similar to what happens if you move your finger across a flame. If you move it quickly, you don’t risk not to be burned, but if you drag it slowly over the flame, your finger will reach a higher temperature,” says AlAlawi.

The MIT team collaborated with researchers at TU Delft 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 sensitivity properties to determine the exact nozzle speed that will achieve certain colors, shades or textures in the printed object.

“There are many inputs that can affect the results we get. We are modeling something very complicated, but we also want to make sure the results are accurate,” says AlAlawi.

The team searched the scientific literature to determine appropriate heat transfer coefficients for a set of unique materials, which they incorporated into their model. They also had to deal with a set of unpredictable variables, such as the heat that could be dissipated by fans and the air temperature in the room where the object is printed.

They integrated the model into a user-friendly interface that simplifies the scientific process, automatically translating the pixels of a manufacturer’s 3D model into a set of machine instructions controlling the speed at which the object is printed and passed back through the dual nozzles.

Faster, finer manufacturing

They tested their approach with three heat-sensitive filaments. The first, a foaming polymer whose particles expand when heated, produces different shades, translucency and textures. They also experimented with a filament filled with wood fibers and another with cork fibers, both of which can be carbonized to produce increasingly darker shades.

The researchers demonstrated how their method could produce objects like partially translucent water bottles. To make the water bottles, they passed the foaming polymer at low speeds to create opaque areas and at higher speeds to create translucent areas. They also used the foaming polymer to make a bicycle handle with varying roughness to improve the rider’s grip.

Trying to produce similar objects using traditional multi-material 3D printing took much longer, sometimes adding hours to the printing process, and consumed more energy and materials. Additionally, modulated speed ironing could produce fine-grained gradients of shades and textures that other methods could not achieve.

In the future, researchers want to experiment with other thermally sensitive materials, such as plastics. They also hope to explore the use of modulated speed ironing to modify the mechanical and acoustic properties of certain materials.

This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news in MIT research, innovation and education.