UltiCasting team

Using Ultimaker to cast silicone for soft robotics

By modifying an Ultimaker 2+ 3D printer, students from Delft University of Technology have discovered a way to cast silicone for soft robotics. This has huge implications for soft actuators, and for the medical sector. Read on to learn more.

Taking 3D printing further

Experts are continually discovering new ways to use 3D printing, which has significant implications for many industries.

Silicone is of particular interest. It’s extremely versatile and can be used to create soft robotics – like the world’s first fully autonomous soft-bodied robot. However, silicone 3D printing was always considered an impossibility – until now.

Casting silicone using a 3D printed shell

Students from Delft University of Technology have discovered a way to 3D print with silicone, using a 3D printed shell. The team has called the new method, which was exhibited at the Advanced Prototyping Science Fair at the Industrial Design Engineering Faculty, UltiCast. It blends 3D printing with traditional casting methods – using a modified Ultimaker 2+ to simultaneously 3D print a plastic mold, then fill the mold with a two-component silicone mix.

casting silicone

How does it work?

In ideal circumstances, the team firstly designs a geometry with a predefined internal cavity – which allows for the ‘soft robotics actuation’. This deforms the material when subjected to air pressure.

After this, the design is loaded to the slicer tool, with the PVA printing interruptions defined at set heights. The nozzle is primed at a set location, retracting the silicone so it doesn’t spill when moving to the printed PVA mold.

It fills the mold with a calculated volume of silicone, before retreating to allow the PVA mold to be built further.

silicone casting


The technology wasn’t without its challenges. The biggest obstacle the team faced was being able to integrate as many features into the slicer as possible, whilst still being able to print at just the single touch of a button. To resolve this, the team created a specialized code – which automatically slices the 3D printed mold and determines how much silicone is required to fill it.

Another problem was removing the mold after the casting was complete. By using PVA, which is water soluble, they could easily extract the silicone by dissolving the mold in water.

To achieve this, they used an Ultimaker 3D printer, which they hacked and rebuilt almost entirely. When asked why they chose Ultimaker, the team said:

As Ultimaker is a well-established brand and an open source tool, it allows perfectly for the development of such add-ons. With the base printer as a very accurate printing device, it serves perfectly for customization and experimentation. The reliability of the Ultimaker is also top-notch. 

The implications

This remarkable innovation has big implications. Ulticasting makes it possible to print a soft actuator much more quickly, and with more design freedom than traditional casting methods. It’s also versatile. Hard and soft materials can be mixed in a single print. For example, in a recent experiment, the team successfully managed to print a hard skeleton inside soft silicone.

“3D printing offers a variety of applications, soft robotics being one of them,” says coordinator Jouke Verlinden. “It allows you to make things that are impossible with traditional robotics.”

It allows for the rapid, low-cost development of customized soft robotic grippers and orthotics – which are of tremendous value to the medical industry. By being able to create structures with both rigid and flexible components, users can create complex, anisotropic behaviors in soft robotics, and can integrate actuators and sensors.

Rob Scharff, a member of the Ulticast team, adds: “You get a lot of freedom to personalize the behavior of robots with geometry and materials.” This means being able to make flexible robot limbs and custom-designed grippers; medical aids that could help those suffering from debilitating conditions such as localized paralysis, arthritis or related injuries.

To find out more about this fascinating breakthrough, and to watch a video of the modified Ultimaker in action, visit their website.

3D printing in research