(Nanowerk News) Manufacturers of smart medical devices, smart robots, and other products with smart sensors can simplify the design and fabrication of their devices using a patent-pending Purdue University method that combines filament piezoelectric polling and 3D printing in a single process.
Traditional sensor materials have piezoelectric properties that make them suitable for making smart sensors. Applying stress in one direction produces stress in another. Although these materials measure how much pressure is applied, which is one of the sensor’s basic properties, they cannot be used in 3D printing.
3D printing, also known as additive manufacturing, has several advantages over traditional manufacturing, including customizing part shapes and geometries beyond planar options. However, the polyvinylidene difluoride (PVdf) filaments used in 3D printing do not have strong piezoelectric properties. The dipoles are randomly oriented, which creates less voltage. As a result, the traditional PVdf filament is not a good stress indicator, and the electric polishing must be carried out in post-processing treatment, which increases time and cost.
Purdue researchers at the Purdue Polytechnic Institute have combined 3D printing and electrification into a single process called electropolling-assisted additive manufacturing, or EPAM. This aligns the dipole in the PVdf filament during printing, leading to a better indication of the applied voltage. This allows 3D printed components to have strong sensing capabilities and adaptable shapes. Importantly, it saves time and money.
This research was published in Advanced Engineering Materials (“Effect of Additive Manufacturing on Capacitive Temperature Sensors Based on β-Phase Poly(Vinylidene Fluoride)”) And Additive Manufacturing (“Electric polling assisted additive manufacturing technique for piezoelectrically active poly(vinylidene fluoride) films: Towards fully three-dimensional printing functional materials”).
Robert Nawrocki, an assistant professor in the School of Engineering Technology at Purdue Polytechnic Institute, said the EPAM process completes stretching and polling simultaneously, which are necessary conditions for polarization.
“During the EPAM process, stretching of the liquid PVdF rod rearranges the amorphous strands in the plane of the film, and the applied electric field aligns the dipole in the same direction,” says Nawrocki. “EPAM processes can print free-form PVdF structures and induce the formation of β-phase, which is mainly responsible for the piezoelectric response.”
Jose M. Garcia-Bravo and Brittany Newell, associate professor in the School of Engineering Technology, Nawrocki and PhD candidate Jinsheng Fan successfully printed a PVdf force sensor with a fused deposition modeling 3D printer with a corona electric field setup.
“Piezoelectric activity, measured in picocoulomb per newton, or pC/N, is calculated based on the output voltage of the piezoelectric,” said Nawrocki. “The average piezoelectric activity of EPAM-printed PVdF films is 47.76 pC/N, or about five times higher than unpolished 3D printed films, of 9.0 pC/N. The piezoelectric activity of unpolished 3D printed PVdF films shows that 3D printing in the absence of an electric field does not produce dipole alignment.”
The next step to commercialize the EPAM method is to create a single 3D printer that can print all sensor components, including the direct polar PVdF, the electrodes, as well as the structure.