Despite widespread and growing popularity, it’s important to realize that additive manufacturing (AM) is still a young technology—and that most of its potential remains untapped. Carolyn Seepersad spends her days exploring such possibilities.
A mechanical engineering professor at The University of Texas (UT) at Austin, Seepersad is taking this decades-old technology in novel directions while attempting to solve some of its thorniest problems. Reactive extrusion.
Volumetric powder-bed fusion. Large-scale, high-velocity stereolithography. These are just a few of the AM technologies that Seepersad, her students, and fellow faculty members are developing at the university’s Cockrell School of Engineering.
She’s in good company. One of her mentors and colleagues is Joe Beaman, the 3D-printing pioneer who coined the term “solid free-form fabrication,” and, with student Carl Deckard, developed selective laser sintering during the mid-1980s.
“We have a long history of additive manufacturing at UT Austin and continue to do extensive research into the printing of polymers, metals, and ceramics,” she said.
Blazing her own AM trails, Seepersad is mostly focused on endowing materials with unique properties that can only be achieved through 3D printing. But she’s also active in developing new technologies. For instance, she and her colleague Mehran Tehrani are working with their graduate students on reactive-extrusion additive manufacturing, or REAM.
Mechanically similar to fused deposition modeling (FDM), the process uses a two-part thermoset polymer (like some commercial epoxies) that is mixed on demand, then squirted onto a substrate or build plate. Any similarities to FDM end there, however, because REAM is about two orders of magnitude faster than desktop printers. For example, printing one of the school’s signature Longhorn-shaped test pieces—measuring 230 mm from horn to horn and 16 mm thick—took less than three minutes, compared to “hours” using traditional FDM methods and materials.
Even more impressive is the fact that the Longhorn and other REAM parts have much less anisotropic mechanical properties (varying in magnitude according to the direction of measurement), due to the inter-layer crosslinking of polymer chains. “We can also mix in additives—magnetic particles is one example, as is carbon fiber—that give the part additional strength or functionality,” Seepersad explained.
Seepersad’s group is collaborating with Penn State University on an NSF-funded LEAP HI project (Leading Engineering for America’s Prosperity, Health, and Infrastructure) to produce functionally graded “active” materials via REAM. The joint effort will allow them to build smart parts that change their shape based on specific stimuli, a capability she suggested is suitable for a range of applications, including the creation of medical devices that adjust to a patient’s anatomy, increasing comfort and reducing the risk of infection.
Another evolutionary AM project involves the stereolithographic (SL) printing of high-viscosity resins, a technology developed in partnership with Lawrence Livermore National Lab by Seepersad, her colleague Rich Crawford, and their graduate students Nick Rodriguez and Hongtao Song. The process is similar to the “bottom-up” approach common with several brands of commercial SL machines, but with several adjustments to compensate for the peanut butter-like viscosity of the polymer resins.
These include an LED/LCD curing and patterning system that delivers “lots of light” and a variable tensioning device that gently separates parts from a Teflon film sitting atop the build plate. The latter works much like “peeling away a Band-Aid,” she said, noting this was necessary to eliminate any chance of damaging delicate or elastomeric parts during the build process. The unique light system, on the other hand, circumvents an even more troublesome event: melting the LED/LCD light source.
“Curing high-viscosity resins requires significant amounts of light energy,” Seepersad said. “But, unfortunately, the film polarizers typically used to create the patterns in this type of SL printer absorb much of that energy. So to avoid overheating and possibly destroying the LCD light patterning device, we switched to a wire-grid polarizer, which reflects energy rather than absorbing it.
“This way, our LCDs don’t heat up as much and we get greater illumination,” the professor continued. “It also allows us to print reasonably large parts, at least by stereolithography standards. Our current machine, which I believe is one of a kind, has a build area 20 inches square.” Laughing, she added, “It’s almost big enough to print an entire herd of Longhorns.”
Seepersad, who is named on the patents for these and several other inventions, began her studies at West Virginia University in 1992. She was named a Rhodes Scholar at the University of Oxford, then earned a Ph.D. in mechanical engineering at the Georgia Institute of Technology. In 2005, she took a position with UT Austin as an assistant professor, and has been there ever since.
In addition to AM, Seepersad works on engineering design research and topology optimization, both of which have gradually taken on an additive flavor. One of her current projects involves interactive design exploration, where users can adjust and “play with” 3D-printed structures to see the effect changes have on performance.
“I’ve also done quite a bit of work in meta-materials design, which looks at how a material’s structure—as opposed to its composition—affects its functional properties,” Seepersad added. “That work was in collaboration with fellow professor Mike Haberman, and led to one of our first patents.”
That patent describes “negative stiffness honeycomb materials,” which are ideally suited to 3D printing in metal or plastic and should be of particular interest to anyone with a child in Little League baseball. That’s because these 3D-printed constructions “snap through” on impact, providing recoverable energy absorption capabilities that could one day be applied to motor vehicles, spacecraft instrumentation, and, yes, sports helmets and other forms of personal protection equipment. “We can engineer these to reduce an object’s acceleration threshold by an order of magnitude,” Seepersad said.
Thanks to Seepersad’s ingenuity and devotion, UT opened the Center for Additive Manufacturing and Design Innovation (CAMDI) in March 2020, appointing her as its director. And even though her new job title came “right at the beginning of COVID,” Seepersad didn’t let that slow her down.
CAMDI brings students, researchers, and faculty together under one roof, expanding the school’s commercial AM capabilities and resources. These include a Metal Powder Bed Fusion Lab with EOSINT M280 and Renishaw AM250 Direct Metal Laser Sintering printers, a Liquid Polymer Lab that’s home to a Stratasys J750 Digital Anatomy Printer and 3D Systems SLA 5000, along with a Metrology Lab boasting structured light scanning, load-testing equipment, and a Zeiss Spectrum coordinate-measuring machine.
Such facilities are crucial to meeting industry challenges. Considering her multiple patents and papers, it’s ironic that Seepersad points to better design capabilities as one of the more urgent needs. Recent advances in topology optimization and generative design notwithstanding, it’s a sad fact that “we can print a lot more than we can design,” she noted.
“Think about the ability to place materials exactly where you want them, or even to modify their composition and mechanical properties from place to place,” Seepersad continued. “Our current design tools are still playing catch-up in many respects.”
People interact daily with products made via traditional manufacturing technologies, limiting our ability to “think additively,” she said. Until the next generation of designers enters the workforce—young people unfettered by preconceived manufacturing notions and able to wrap their heads around the spatial and material complexities that come with 3D printing—the industry will fail to fully leverage AM’s immense design freedoms.
Thanks to Seepersad and others, that paradigm is shifting. “I think that’s probably been one of our biggest bottlenecks, but the good news is, many of our students have grown up with 3D printing. They’ve used it in high school.
Some have even used it in middle school. And aside from our center, UT Austin has a huge maker space called the Texas Inventionworks where students can spend time with 3D printers and laser cutters and similarly advanced technology. We’ve begun to incorporate that into our curriculum, giving students multiple opportunities for hands-on experience.”
She also challenges students, wherever they are, to design products that can’t be made via conventional means. “More than one student has told me they completed the assignment on their personal 3D printer,” she said. “So despite my earlier comments about bottlenecks and the complexities of additive design, I think the next generation of designers is already here to a certain extent. It’s our job to nurture them and give them all the tools they need to succeed.”
