New 3D printing technology allows you to create unique objects quickly and with less waste

Using a 3D printer like an iron, researchers can precisely control the color, hue and texture of the objects they create using just one material

Multimaterial 3D printing allows manufacturers to produce custom devices with multiple colors and a variety of textures. However, this process can be time-consuming and wasteful, as existing 3D printers must switch between multiple nozzles, often finishing with one material before starting to deposit another.

Researchers from the Massachusetts Institute of Technology and Delft University of Technology have presented a more efficient, less wasteful and highly accurate technique that uses heat-responsive materials to print objects with multiple colors, shades and textures in a single pass.

Their method, called “variable speed ironing,” uses a 3D printer with two nozzles. The first nozzle applies the thermoset filament, and the second passes over the printed material to activate certain reactions, such as changes in clarity or roughness, using heat.

By controlling the speed of the second nozzle, the researchers can heat the material to specific temperatures, fine-tuning the color, hue and roughness of the thermoset filaments. It is important that this method does not require any hardware modifications.

The researchers developed a model that predicts the amount of heat that an ironing attachment will transfer to the material depending on its speed. Based on this model, a user interface was created that automatically generates printing instructions to achieve color, shade and texture specifications.

With variable speed ironing, you can create artistic effects by changing the color on your printed object. This technique also creates textured handles that are easier to grasp for those with weak hands.

“Today we have desktop printers that use a clever combination of multiple inks to create different 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 much more diverse characteristics of 3D printed objects,” says Mustafa Doga Doğan PhD '24, co-author articles about ironing with modulated speed.

This project is a collaboration between the research groups of Jenja Doubrowski, assistant professor at TU Delft, and Stefanie Müller, TIBCO Career Development Professor in the Department of Electrical Engineering and Computer Science (EECS) at MIT and a member of the Computer Science and Artificial Intelligence Laboratory (CSAIL) at MIT. . Dogan worked closely with lead author Mehmet Ozdemir of TU Delft, Marwa Al-Alawi, a graduate student in mechanical engineering at MIT, and José Martinez Castro of TU Delft. The research will be presented at the ACM Symposium on User Interface Software and Technologies.

Speed ​​modulation for temperature control

The researchers launched the project to explore the best ways to achieve multifunctional 3D printing using a single material. The use of thermoset filaments has shown promise, but most existing methods use a single nozzle for printing and heating. Before applying material, the printer should always first heat the nozzle to the desired temperature.

However, heating and cooling of the nozzle takes a long time, and there is a danger that the filament in the nozzle may break when reaching higher temperatures.

To prevent these problems, the team developed an ironing technique in which the material is printed using one nozzle and then activated by a second, empty nozzle, which only warms it up. Instead of adjusting the temperature to cause the material to react, the researchers maintain a constant temperature of the second nozzle and vary the speed at which it moves across the printed material by lightly touching the top of the layer.

“When we adjust the speed, it allows the printed layer we are ironing to reach different temperatures. This is similar to what happens when you run your finger across a flame. If you move it quickly, you may not get burned, but if you move it slowly across the flame, your finger will reach a higher temperature,” says Al-Alawi.

The MIT team, together with researchers from TU Delft, developed a theoretical model that predicts how fast the second nozzle must move to heat the material to a certain temperature.

The model correlates the material's exit temperature with its heat-responsive properties to determine the exact nozzle speed that will achieve specific colors, shades, or textures in the printed object.

“There are a lot of inputs that can influence the results we get. We are modeling something very complex, but we want to make sure that the results are accurate,” says Al-Alawi.

The team dug into the scientific literature to determine the correct heat transfer coefficients for the set of unique materials they built into their model. They also had to take into account many unpredictable variables, such as the heat dissipated by the fans and the air temperature in the room where the object was being printed.

They built the model into a user-friendly interface that simplifies the scientific process by automatically translating the 3D model's pixels into a set of machine instructions that control the speed of printing and ironing the object using dual nozzles.

Faster and finer production

They tested their approach with three thermoset filaments. The first, a foaming polymer with particles that expand when heated, allowed for a variety of shades, translucency and texture. They also experimented with thread filled with wood fibers and thread with cork fibers, which can be charred to produce increasingly darker shades.

The researchers demonstrated how their method could create partially transparent objects, such as water bottles. To make the water bottles, they ironed the foaming polymer at low speed to create opaque areas and at higher speed to create translucent ones. They also used a foaming polymer to make the bike handle with different roughness to improve grip.

Attempting to produce such objects using traditional multi-material 3D printing took much longer, sometimes adding hours to the printing process, and consumed more energy and materials. Additionally, variable speed ironing allows you to create subtle gradients of shades and textures that other methods cannot achieve.

In the future, the researchers want to experiment with other heat-sensitive materials, such as plastic. They also hope to explore the possibility of using variable speed ironing to change the mechanical and acoustic properties of some materials.