Purdue University researchers have developed a method to embed electrically-conductive particles, or sensors, in 3D printed filament polymers and disperse them evenly.
The patent-pending wet-mixing method could be used for a "large variety" of products and uses, including assessing materials and parts themselves, Brittany Newell, associate professor at Purdue's School of Engineering Technology, told Plastics News in an interview. "By embedding a sensor within the 3D printed material itself, we can determine if the part is doing what it's supposed to."
Traditional foil-type strain gauges are adhered to the surface of a printed part with an epoxy resin, Newell said.
Sensor particles used in the new mixing method are too small to be seen without a microscope, allowing a printed part to maintain strength it would have sacrificed for large, built-in sensors, she added.
"A limitation of application of 3D printed parts has been in their durability," Newell said. "Generally, we apply [a] strain gauge [on the surface of the] part or apply it to the top and bottom of the part to get information on overall strain across the part. However, the middle and internal structures are never monitored since the gauges are glued to the surface.
"You're assuming constant values throughout, where here you can put it in the center of the object," she said. "With this development, we can continually monitor the structural health of the part with the sensor embedded in the print."
Manufacturers and researchers can use the method to create "complex 3D structures with embedded strain gauges, rapidly moving traditional prototype pieces into fully functional and structurally assessable parts," she added.
"By adding this conductive material directly to the 3D prints, we can monitor things like deformation of the actuator itself, so you know where in space the material is," Newell said. "You can look at things like grip.
"Since we have enhanced the electrical properties of the material, there's always a tradeoff between the mechanical and electrical properties," she said. "We can actually optimize for specific sensing ranges, which allows us to better balance the mechanical and electrical needs and … vary the amount [of conductive components] to tune our sensors."
Users can also "plan the path for the signal to come through, almost as if it was like a wire coming out," Newell said.
"When we adjust the filament as it is being manufactured, and we can control the electrical mechanical properties, that allows us to check for certain sensing ranges," she added. That "enhances the sensor's ability to detect problems or changes."
The wet-mixing method could expand sensor development in general, Newell said.
"Usually people think of sensors [as] discrete things," Tyler Tallman, assistant professor Purdue's School of Aeronautics and Astronautics said. "We're actually printing the material as a sensor, so it's possible to make the entire component or structure, or whatever you're printing out of the sensing material. In that sense, the entire thing is a sensor, rather than a single point
"We can also print whatever component entirely out of the material so it's all self-sensing," Tallman said. "Then you're no longer constrained by point-base sensors."