Multi-material 3D-Printer for Rapid Prototyping
53
embedded in the PLA. Thanks to this design, more than 2.5 bar of pressure can be applied
without any leakage at the material interface.
4 Conclusion
In order to address the ongoing challenge to fabricate complex functional parts for
the research of soft robots, in particular how to combine different materials in complex geometries, this paper has presented the development of a novel 3D printer with
on demand tool change. The developed locking mechanism is adaptive to quite large
deviations of the counterpart and requires very little adjustment. In combination with the
kinematic coupling, the locking mechanism enables the device to switch rapidly between
the prepared tools. The directly driven FFF-print-heads that have been designed for this
purpose showed an extrusion precise enough to create airtight chambers, which can be
used as pneumatic actuators. The fabrication of cuboid cavities is hampered by hanging bridges in the first layers of the ceiling and therefore limits top layer thinness of a
chamber, which is still airtight. Since the expandable sides of the chamber required at
least two layers they were limited to 0.8 mm when using a 0.4 mm nozzle. Changing the
orientation of the actuating membrane to the bottom side pushed these limits to 0.3 mm.
The disadvantage is that all active elements per specimen have to be located there. This
problem could be solved by using one print-head to fill cavities and gaps between membranes with soluble support filament. This approach could allow a variable number of
thin actuating layers to be printed within one process as long as they are orientated
parallel to the X/Y plane. The flexible TPU membrane integrated in a housing of stiff
PLA has demonstrated the suitability of the printer for multi-material fabrication. The
positively tested concept of embedding a hook-like structure in order to overcome the
lack of chemical bonding between PLA and TPU could be modified in many ways and
has the potential to lead to an all-in-one print of much more complex functions. Since the
coupling mechanism is based on a rudimentary interface, the design of other compatible
tools with different work principles is relatively feasible. Some conceivable examples of
tools include an inkjet printhead, syringe extruders for high viscous substances or drills.
This novel FFF-multi-material printer and the printed demonstrators highlight the
great potential to create yet unbuilt biomimetic structures and multi-material systems.
Acknowledgement. Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research
Foundation) under Germany’s Excellence Strategy – EXC-2193/1 – 390951807. SC, FE & TS are
grateful to the Deutsche Forschungsgemeinschaft for the funding our research.
References
Coyle, S., Majidi, C., LeDuc, P., Hsia, K.J.: Bio-inspired soft robotics: material selection, actuation,
and design. Extreme Mech. Lett. 22, 51–59 (2018). https://doi.org/10.1016/j.eml.2018.05.003
Gul, J.Z., et al.: 3D printing for soft robotics - a review. Sci. Technol. Adv. Mater. 19(1), 243–262
(2018). https://doi.org/10.1080/14686996.2018.1431862
53
embedded in the PLA. Thanks to this design, more than 2.5 bar of pressure can be applied
without any leakage at the material interface.
4 Conclusion
In order to address the ongoing challenge to fabricate complex functional parts for
the research of soft robots, in particular how to combine different materials in complex geometries, this paper has presented the development of a novel 3D printer with
on demand tool change. The developed locking mechanism is adaptive to quite large
deviations of the counterpart and requires very little adjustment. In combination with the
kinematic coupling, the locking mechanism enables the device to switch rapidly between
the prepared tools. The directly driven FFF-print-heads that have been designed for this
purpose showed an extrusion precise enough to create airtight chambers, which can be
used as pneumatic actuators. The fabrication of cuboid cavities is hampered by hanging bridges in the first layers of the ceiling and therefore limits top layer thinness of a
chamber, which is still airtight. Since the expandable sides of the chamber required at
least two layers they were limited to 0.8 mm when using a 0.4 mm nozzle. Changing the
orientation of the actuating membrane to the bottom side pushed these limits to 0.3 mm.
The disadvantage is that all active elements per specimen have to be located there. This
problem could be solved by using one print-head to fill cavities and gaps between membranes with soluble support filament. This approach could allow a variable number of
thin actuating layers to be printed within one process as long as they are orientated
parallel to the X/Y plane. The flexible TPU membrane integrated in a housing of stiff
PLA has demonstrated the suitability of the printer for multi-material fabrication. The
positively tested concept of embedding a hook-like structure in order to overcome the
lack of chemical bonding between PLA and TPU could be modified in many ways and
has the potential to lead to an all-in-one print of much more complex functions. Since the
coupling mechanism is based on a rudimentary interface, the design of other compatible
tools with different work principles is relatively feasible. Some conceivable examples of
tools include an inkjet printhead, syringe extruders for high viscous substances or drills.
This novel FFF-multi-material printer and the printed demonstrators highlight the
great potential to create yet unbuilt biomimetic structures and multi-material systems.
Acknowledgement. Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research
Foundation) under Germany’s Excellence Strategy – EXC-2193/1 – 390951807. SC, FE & TS are
grateful to the Deutsche Forschungsgemeinschaft for the funding our research.
References
Coyle, S., Majidi, C., LeDuc, P., Hsia, K.J.: Bio-inspired soft robotics: material selection, actuation,
and design. Extreme Mech. Lett. 22, 51–59 (2018). https://doi.org/10.1016/j.eml.2018.05.003
Gul, J.Z., et al.: 3D printing for soft robotics - a review. Sci. Technol. Adv. Mater. 19(1), 243–262
(2018). https://doi.org/10.1080/14686996.2018.1431862