Allowing users to create objects from simple toys to custom prosthetic parts, plastics are a popular 3D printing material. But these printed parts are mechanically weak — a flaw caused by the imperfect bonding between the individual printed layers that make up the 3D part.
Researchers have 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.
Plastics are commonly used for extrusion 3D printing, known 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 but the 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: an oven will heat everything, so a 3D-printed part can warp and melt, losing its shape.
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. To apply electricity as the object is being printed, the currents must overcome a tiny space of air between the printhead and the 3D part. One option to bridge this air gap is to use metal electrodes that directly touch the printed part but this contact can introduce inadvertent damage to the part.
Instead, the team generated a beam of charged air particles, or plasma, that could carry an electrical charge to the surface of the printed part. This technique allowed electric currents to pass through the printed part, heating the nanotubes and welding the layers together. With the plasma technology and the carbon nanotube-coated thermoplastic material in place, the team added both these components to conventional 3D printers. When they tested the strength of 3D-printed parts using the new technology, they found that strength was comparable to injection-molded parts.
With the technology, users can print a custom part, like an individually tailored prosthetic, and the heat-treated part will be much stronger than before.