Simple toys to custom prosthetic parts are made from plastic, which is also a popular 3D printing material. However, these printed parts are mechanically weak — a flaw caused by the imperfect bonding between the individual printed layers that make up 3D-printed parts.
Researchers at Texas A&M University, in collaboration with scientists from Essentium, Inc., have now developed the technology needed to overcome 3D printing’s “weak spot.” By integrating plasma science and carbon nanotube technology into standard 3D printing, the researchers welded adjacent printed layers more effectively, increasing the overall reliability of the final part.
“Finding a way to remedy the inadequate bonding between printed layers has been an ongoing quest in the 3D-printing field,” said Dr. Micah Green, associate professor in the Artie McFerrin Department of Chemical Engineering. “We have now developed a sophisticated technology that can bolster welding between these layers, all while printing the 3D part.”
A full description of their findings is described in the February issue of the journal Nano Letters.
Plastics are commonly used for extrusion 3D printing, known technically as fused-deposition modeling. In this technique, molten plastic is squeezed out of a nozzle that prints parts layer by layer. As the printed layers cool, they fuse to one another to create the final 3D part.
However, studies show that these layers join imperfectly; printed parts are weaker than identical parts made by injection molding where melted plastics simply assume the shape of a preset mold upon cooling. To join these interfaces more thoroughly, additional heating is required, but heating printed parts using something akin to an oven has a major drawback.
“If you put something in an oven, it's going to heat everything, so a 3D-printed part can warp and melt, losing its shape,” Green said. “What we really needed was some way to heat only the interfaces between printed layers and not the whole part.”
To promote inter-layer bonding, the team turned to carbon nanotubes. Since these carbon particles heat in response to electrical currents, the researchers coated the surface of each printed layer with these nanomaterials. Similar to the heating effect of microwaves on food, the team found that these carbon nanotube coatings can be heated using electric currents, allowing the printed layers to bond together.
When the researchers tested the strength of 3D-printed parts using their new technology, they found that their strength was comparable to injection-molded parts.
This work is supported by funds from the National Science Foundation.
Multidisciplinary collaboration
The primary author of this research is Dr. C. Brandon Sweeney, a former Texas A&M materials science and engineering student in Green’s laboratory. He is the head of research and development and co-founder at Essentium, Inc.
The research team also collaborated with Dr. David Staack, associate professor in the J. Mike Walker ‘66 Department of Mechanical Engineering, to generate a beam of charged air particles, or plasma, that could carry an electrical charge to the surface of 3D printed parts to allow electric currents to pass through printed parts, heating the nanotubes and welding the layers together.