The nozzles, which are controlled along the X and Y axis, can spray materials on top of and around each other. They lay the material onto the substrate (controlled on the Z axis) with 235 microns accuracy. Initially, Gou utilized a spray infiltration process that used a vacuum to pull the solvent through a filtered membrane. However, the process now uses an evaporation method to remove the solvent.
There are several existing additive manufacturing processes: Fused deposition modeling uses heat to extrude the thermoplastic to build up the necessary layers, and PolyJet technology uses atomized droplets like SDM and UV light to cure the resin. Three others – digital light processing, stereolithography and selective laser sintering – use lasers as the processing mechanism. In contrast, SDM deposits both nanomaterials and polymers by evaporating the solvent from the solution. Gou says that SDM also allows for the use of multiple materials to create the desired composition, distribution and microstructure of a nanocomposite. For example, SDM can create a nanocomposite that contains both CNT and graphene in a side-by-side and/or layer-by-layer structure.
According to Gou, one of the major challenges in developing SDM was the accumulation of the nanoparticles in the nozzles, which caused clogging and halted production of samples for testing. Another challenge was developing an effective nozzle control method to precisely deliver the right material to the correct location at a specific time and in the right amount.
The project, which is funded through the Florida High Tech Corridor (FHTC), began 18 months ago. During stage one, Gou and his team designed, built, tested and evaluated the SDM machine. That work is now completed, and they are moving on to stage two – material formulation for improved printability and final properties. The first test product fabricated by SDM was a shape memory polymer nanocomposite that was actuated using Joule heating (passing an electric current through a conductor to release heat). “The digital fabrication of the nanocomposites to a desired location allowed for a better distribution of the heat throughout the sample,” says Gou.
Although it will be a few years until SDM is ready for commercialization, Gou says the new digital fabrication process shows promise for a variety of industries. For example, SDM could be used to fabricate digital nanocomposites for Joule heating applications such as an aftermarket film for deicing airplane wings without the use of chemicals. This composite film could also function as a “power film” to provide controlled heat to cure composite structures out of an autoclave. Other applications may include flexible electronics for phones, watches and other wearable devices and strain sensors for structural health monitoring and damage detection of composite structures.
“Digital nanocomposites are the next generation of composites. They will integrate structural performance with multi-functionalities all in a single manufacturing operation,” says Gou. “The SDM process can tell the computer what composite product you want and then produce it accurately and efficiently. In other words, what you get will be exactly what you see on the computer.”