4D Printing Breakthrough Achieved in ESA-Funded Project

For over a year Zortrax has been a prime contractor of the European Space Agency in a project aimed at developing new 4D printing technologies for space industry. Now, the project is done, our research and development teams achieved major breakthroughs in the field and we are finally ready to tell you everything about it. Strap in and enjoy the ride.

What is 4D Printing

3D printing is an additive manufacturing technology that enables building physical, three-dimensional objects layer by layer based on the digital model. The forth additional dimension added in the 4D printing technology is time. 4D printed objects can change their properties like geometry in response to various stimuli, be it temperature, moisture, electric current, and many more. Imagine an origami-like structure that stays folded in room temperature but unfolds when heated up.

Zortrax M300 Dual 3D printer used for making 4D printed mechanisms in the ESA project.

4D printing generated a lot of interest in the space industry because, in theory, the technology could enable engineers and mission designers to reduce weight of deployable structures like antennas, booms, or various sensors. The weight of such structures made in a traditional way is always a sum of the structure itself and the mechanism that is supposed to deploy it. Astronika, one of Zortrax’s key partners in space industry, can make such booms and antennas incredibly light. But if it was possible to get rid of the deployment mechanisms altogether, they could be made even lighter and smaller.

Challenges of 4D printing

Now, 4D printing made headlines when the team of researchers working at MIT made deployable 4D printed structures that could move when heated to a certain temperature back in 2013.

While their results looked impressive, there were a few apparent problems that needed solving before this technology could find any real-world applications.

• Shape changing was triggered by the environment’s temperature which heated up the entire structure at once.
• The process was hardly controllable – it got triggered when the environment temperature reached certain level and you can’t always control the environment.
• Shape changing started in relatively low temperature of 40 degrees Celsius
• Because the shape changing was triggered by the environment, there was no way to deploy such structures sequentially which limited their applications.

Zortrax, working with ESA, managed to solve all these problems. Here’s how.

Selecting the Right Materials

Manufacturing of 4D printed mechanisms requires three basic components. These are:

• Right materials providing the shape memory effect.
• The right software which enable fabricating 4D printed parts.
• The right 3D printer which can physically make the 4D printed parts.

The development process at Zortrax started with choosing the right filaments for the job. For the RnD team selected a pool of shape memory polymers that would drive the movement in the system and a pool of electrically conductive filaments that would act as an electrically activated heater activating the shape memory effect.

4D printing technology demonstrators delivered to ESA by Zortrax.

Right from the get-go, it became apparent that commercially available shape memory filaments had glass transition temperature of up to 55 ℃ which was not enough for space applications. A 4D printed mechanism with such filaments would activate on its own in temperatures exceeding 55 ℃ which happens quite often on Low Earth Orbit when the spacecraft is exposed to sunlight.

For this reason, Zortrax made a custom shape memory filament which had glass transition temperature of 75 ℃ which was 50% higher than anything available on the market. The material got delivered, thoroughly tested, and found suitable for proof-of-concept 4D printed systems.

Choosing the right conductive material was easier since multiple off-the-shelf filaments met the requirements. After an extensive test campaign where thermal and electrical properties of these filaments were tested, the FIBERFORCE NYLFORCE Conductive was selected as the material to heat the shape memory polymer in the 4D printed mechanisms.

Bending movement 4D printing technology demonstrator in the testing setup.

In the last step, the Zortrax RnD team checked if the two selected polymers could be printed in the bi-material 3D printing mode that enables manufacturing of parts made with two different materials. This bi-material 3D printing mode was made possible by combining experimental version of Z-SUITE software, initially developed specifically for ESA, and the dual extrusion M300 Dual 3D printer which could operate with two printing heads at once.

The Making of 4D Printing Demonstrators

Under ESA contract, Zortrax had to develop three 4D printing demonstrators, each showcasing different type of electrically activated movement. These types of movement were:

• Bending.
• Torsion.
• Deployment.

Work on the bending movement demonstrator began with designing simple, rectangular shapes with electrically conductive heating core and outer layers made with the shape memory material.

From those simple shapes the RnD team moved to more advanced designs, eventually ending up with a bar capable of bending roughly 30 degrees within one minute from turning on the power.

Torsion movement was a little more tricky since it is easier to make 4D printed mechanisms bend rather than rotate when activated. The first shot was a spiral design that would compress and cause the rotary movement in the center.

Spiral design which was the very first iteration of the torsion movement demonstrator made by Zortrax.

This however proved difficult to power up due to long conductive lines. On the other hand, shorter and thinner versions of this design were fragile and couldn’t  generate enough torque.

For this reason the team took a radical step and made an entirely new, spring-like design that had short conductive lines and could generate enough torque to turn the 3D printed chassis even without lubrication or bearings. The mechanism could turn 30 degrees when powered.

Final torsion movement demonstrator. A 3D printed mechanism on the left and a working principle on the right.

The last and most complicated design was deployment movement demonstrator. Zortrax team started with rather elaborate three-leaf membrane with the leaves closing in like a flower upon providing electric current.

Deployment movement demonstrators on the left and spring-like torsion movement demonstrators on the right.

This proved too complicated and and the movement was pretty slow. In the next iteration the number of leaves was reduced to two and then further down to just one. Using two of these one-leaf membranes it was possible to build a single-use reversible system where the shape memory effect of one membrane programmed the movement in another membrane.

This way it was possible to move the system from closed to open to closed again using electric current only.

The Future of 4D Printing in Space

4D printed is a technology which have the potential to revolutionize how mechanisms work in space. Because the movement is an inherent feature of the materials used, there is no need for a separate actuation systems that add weight and therefore increase cost of the mechanism.

With this future in mind, the simple demonstrators made in this ESA project can be used as basic building blocks in larger mechanisms. This means they are easily scalable, can be activated at will, and are incredibly simple which translates into reliability.

Spring-like torsion movement demonstrator installed in a 3D printed case.

Such systems can be used in multiple applications. Single-use array sensors which are scattered over a large area to take measurements in difficult environments where using more expensive materials would make little sense are one example. Other include deployable antennas that could be deployed and folded at will with no actuation mechanisms at all. Using multiple 4D printed building blocks such as the one used as bending demonstrator here, it is possible to make pointing mechanisms which can be controlled with amazing precision.

Of course, there is lots of work still to be done before 4D printed systems go beyond experimental phase and fly on an actual space mission. But what was done here at Zortrax is a solid starting point. The electrically activated 4D printed mechanisms can activated with a push of a button, they can work in any temperature not exceeding 75 ℃, heat can be delivered precisely to chosen points in the mechanism and first steps towards achieving reversibility have been made. The remaining work is fine-tuning and evolution.

4D printing is just one of many exciting ways to use the Zortrax M300 Dual 3D printer. Another one is 3D printing with 316L or 17-4 PH stainless steel. You can learn more about it here.