Making Far Stronger 3D-Printed Thermoplastics

Rapid prototyping with 3D printing is increasingly used for the production of finished products or parts in various industries. But some sectors are not able to integrate this technology except in the manufacture of machining prototypes or test models. Thermoplastic parts manufactured by 3D printing, also called additive manufacturing, are fragile and cannot withstand certain physical constraints.

Brandon Sweeney, Ph.D. student at Texas A&M University’s Department of Materials Science and Engineering, his Ph.D. supervisor Dr. Micah Green, Associate Professor in the Department of Chemical Engineering, and Dr. Mohammad Saed, Assistant Professor in the Department of Computer Science and Computer Engineering at Texas Tech have discovered a way to make 3D printed thermoplastic parts highly resistant and functional.

Sweeney became familiar with 3D printing while working at the Aberdeen Proving Grounds’ Army Research Laboratory in Maryland. He wanted to make this method more efficient in order to eliminate the production phases needed to get from the design process to the manufactured objects.

During manufacture, thermoplastic material is printed using superimposed thin layers. These layers are fragile and can easily crumble, causing weakness in the object and making it less reliable. The material’s fragility is actually caused by the printing process. When molten strands are deposited on the printing plane, the polymer layers are not well bonded to each other, causing delamination of the material and a resulting mechanical failure of the part.

Green had collaborated with Dr. Saed on a project to detect carbon nanotubes using microwaves. Inspired by this study, the three researchers thought of consolidating polymer layers with carbon nanotubes. However, adding this binder, which requires heat to ensure adhesion of the different polymer layers, presented a major drawback—distortion of the object or total meltdown of the material in the furnace. The first solution the team came up with was to use a localized heat source, such as in the welding of metal parts.

Manufacturing Process

In order to integrate the carbon nanotubes with the polymer, a part was added to the 3D printer. With this part, it is possible to wrap the polymer printing filaments with a thin layer of highly conductive ink (CNT ink). When the printer starts, the polymer layers and the CNT ink overlap, forming a laminated and resistant structure. The elements of each layer do not come into contact at this stage. Since each polymer layer is very thin, the researchers used a special microwave device to apply localized heat after printing. The emitted heat is monitored by infrared camera.

Tests showed the reinforced thermoplastic material to be 275% stronger. According to the team, this study paves the way to dielectric properties coupled with the reactions of nanomaterials exposed to electromagnetic fields.

The researchers are now designing a new 3D printer with an integrated electromagnetic welding system, a project that is still in the beta phase. The technology is licensed with Essentium Materials (a local company).

This study, entitled “Welding of 3-D Printed Carbon Nanotube-Polymer Composites by Locally Induced Microwave Heating” was published in the Science Advances journal. Researchers Blake A. Lackey, Martin J. Pospisil, Thomas C. Achee, Victoria K. Hicks, Aaron G. and Moran, Blake R. Teipel also collaborated on this study.