Soft Materials 3D Printer
University of Illinois at Urbana-Champaign
Project Motivation
Soft robotics research is limited by currently available manufacturing methods. Manual techniques such as casting are labor intensive and impose design constraints to accommodate mold removal. Commercially available thermoplastic elastomer filaments for fused deposition modeling (FDM) printing and elastomer resins for stereolithography (SLA) printers are too stiff for use in pneumatic soft actuators.
The goal of this ongoing project is to develop a low-cost multi-material 3D printer for printing soft robotic components.
Printer Design
A commercial FDM printer (Lulzbot TAZ 6) was modified by replacing the FDM tool head with a 3D printed bracket to accommodate up to three liquid dispensing nozzles and a 100 W UV LED curing lamp. The printer is housed inside a polycarbonate enclosure with UV-blocking film to prevent eye damage from UV light.
The dispensing nozzles are attached to perfluoroalkoxy alkane (PFA) tubing that carries the silicone ink from the extruders, situated on top of the safety enclosure, to the tool head. The extruders are commercial high-pressure syringe pumps (Fusion 6000, Chemyx Inc.) that are controlled by the printer’s custom firmware via RS-232 serial communication.
An open-source slicing software (Slic3r 1.3.0) converts digital models to G-code instructions, which are then sent to the printer. The custom firmware sends extrusion commands to the syringe pumps as the stock gantry moves the nozzles across the build plate. Each layer is cured for approximately 30 seconds before the printer proceeds to the next layer.
Ink Development
The 3D printer uses soft and stiff photosensitive silicone-based inks and a water-soluble support ink. The support ink and the curing chemistry of the silicone inks are modeled after the work of Schaffner et al., who mixed vinyl-terminated silicone, a thiol-functionalized crosslinker, and a photoinitiator to achieve the desired mechanical and curing properties [1]. Instead of the photoinitiator used by Schaffner et al., the inks for this printer use a photoinitiator with an absorption peak at 365 nm (Irgacure 819, Ciba Inc.), which is the light wavelength output by a lower-cost UV LED lamp. To thicken the inks and introduce shear-thinning behavior, the inks will include a commercial rheological modifier (THI-VEX, Smooth-On Inc.).
[1] M. Schaffner, J. A. Faber, L. Pianegonda, P. A. Rühs, F. Coulter, and A. R. Studart, “3D printing of robotic soft actuators with programmable bioinspired architectures,” Nat. Commun., vol. 9, no. 1, 2018.