Printing in gel takes 3D printing freeform and enables an undo function
July 29, 2013
The additive layer process of conventional 3D printers means they are usually limited to bottom up fabrication on three axes. The Mataerial printer managed to defy gravity by using a quick-solidifying print material, but now the LA-based NSTRMNT team led by Brian Harms, a Masters student at the Southern California Institute of Architecture, has created a 3D printing process called suspended disposition that gets around gravity by printing objects within a gel. Not only does this allow freeform additive fabrication on six axes, it also enables an "undo" function.
The NSTRMNT 3D printer utilizes a six-axes robotic arm from Stäubli Robotics with a peristaltic pump mounted on it. This injects a light-cured liquid resin into a gel that acts as a support structure for the printed object. The pump's flow rate is controlled by an Arduino, which is coordinated with the motion of the robot to create the prints. The Arduino also controls the pump's flow direction, giving it the ability to delete parts of the printed object by sucking instead of extruding.
After a print is completed, the liquid resin is exposed to ultraviolet light for one to two minutes, which hardens the structure. "We also have UV LEDs mounted on the pump, but in our experience they take far too long to cure the resin," explains Harms. Like printed support structures on traditional 3D printed objects, the gel holds the resin in place until it is cured and ready for removal.
"The gel can be reused many times, as long as it does not dry out," Harms tells Gizmag. "We got in the habit of covering the gel container when not in use, and we could reuse the gel for several weeks. We haven't fully tested the maximum duration for reuse, but I imagine it could be a few months."
To calculate the movements of the robot’s joints, the NSTRMNT printer uses an inverse kinematics solver that Harms developed for Grasshopper (the 3D modeling plugin for Rhino, a 3D CAD program).
"We design our geometry, it is converted to toolpaths, and we run the robot along those paths. But, the robot can be controlled manually using the controller pendant that comes with each robot," Harms tells Gizmag. This allows a user to pause an operating print and move the robot as the pump extrudes resin. "In this way it is a sort of live drawing tool – kind of like an etch-a-sketch in 3D."
At the moment, the NSTRMNT's resolution is about 1/16 of an inch (about 1.6 mm), but the resolution is only reliant upon the diameter of the tube/needle used to extrude the resin, so smaller needles would result in better resolutions.
"The biggest issue we have is actually the tendency for the resin to want to travel up the temporary void the needle creates as it passes through the gel," says Harms. This issue could be resolved by increasing the speed of the robot, but Harms explains that this would require faster extrusion from the pump which would be harder to coordinate cleanly.
The fact that this method of 3D printing can me adjusted and manipulated live allows for a new interface for generating form directly in the physical environment, as opposed to going from computer to fabrication.
"You can inject resin along curving vectors in three dimensions without having to wait for your model to be generated in thin slices," says Harms. Also, because the material is UV-cured and suspended in liquid-form, a designer does not have to commit to a form during a print. Users can alter forms, add components, and even undo bits of their print by removing resin via suction or scooping.
The video below shows the NSTRMNT 3D printer's suspended deposition process in action.
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