LiquiFab – crafting with liquids in weightlessness

The fabrication process

Consider a liquid volume injected into a gravity-free environment (achieved either by neutral buoyancy or in orbit). When floating freely without contacting any other surface, such a volume would take a spherical shape corresponding to its minimum energy. The notion of 'LiquidFab' is that this volume can now be 'sculptured' into other shapes by bringing it in contact with one or more surfaces (mathematically, boundary conditions). The liquid would then take a new shape, corresponding to its new minimum energy configuration that respects the boundary constraints. UV light is then used to cure the polymer, resulting in a solid object.

Key features

LiquidFab is an additive manufacturing approach, but it is neither 3D printing nor molding. 3D printing requires the injection head to visit every voxel, making printing time extremely long for large structures. In LiquiFab, similar to molding, the entire liquid polymer is injected at once and is shaped to yield the final structure. However, in LiquiFab there is no mold. Instead, the boundary elements are used to guide the desired form through surface tension.

LiquiFab objects can be full or hollow, and owing to surface tension are characterized by extreme smoothness, on the order of several angstroms RMS - better than any existing polishing method. Equally important, the method has zero waste – no machining, polishing, or other material-removal techniques are used. The entire liquid volume that is injected is transformed into the object of interest.

Digital design and automation

We have developed a computational package that allows the user to design arbitrary boundary conditions using any CAD software, define the volume of the injected liquid, and obtain an accurate prediction of the three-dimensional LiquiFab object. At the heart of the package is Surface Evolver - a powerful computational tool created by Ken Brakke [Experimental Mathematics, 1992, 1(2), 141–165]. that provides a flexible and dynamic environment for modeling surfaces in three-dimensional space. Users can define surfaces as collections of facets that evolve towards minimal energy states under the influence of specified forces.

This prediction tool is at the basis of our robotic system, that allows the fabrication of large constructs, such as the presented geodesic dome, made of individual and different ‘LiquiBricks’. The computational tools are used to guide the robotic arm, which places the boundary conditions at the correct location and orientation, and injects a suitable liquid volume to produce the desired segment.