NDSU research redefines 3D Printing capabilities

While the 3D printing movement has expanded massively over the past several years, it has always struggled with an inherent disadvantage: the types of materials used in manufacturing are limited in their strength and size. Researchers at NDSU, led by Chad Ulven, professor of mechanical engineering, are working to change that.

The process of manufacturing parts, objects and structures layer by layer with various materials, is an additive process as the 3D printer repeatedly builds up material on a flat surface. The typical plastic 3D printers do not include reinforcement, so the strength and size properties of the items created are limited.

“Witnessing the limitations of 3D printed structures caused my research team to question whether we could discover methods to include short and continuous reinforcement that would allow 3D printers to print structural quality plastic composites to broaden the use case for 3D printed items,” Ulven said.

Adding reinforcement to the materials can help make them stronger without losing the ability to print complex shapes. Some 3D printers can now reliably print thermoplastic composites (plastics with added fibers). However, these materials still have downsides, including their inability to handle high temperatures and lower fiber content, which limits their strength. Thermoset composites (plastics that harden permanently when cured) are more heat-resistant and stronger, thanks to their chemical structure. Adding long, continuous fibers instead of short ones can further strengthen parts.

The team’s research has produced several key advancements in 3D printing through the incorporation of fiber reinforcement, Ulven said. They have developed equipment and methods to integrate short fibers into SLA (Stereolithography)-type resins. SLA-type resins are photopolymer liquids or thermoset polymers that are cured by a light source to create 3-dimensional parts layer by layer. These offer properties like those of thermoplastics, such as ABS or PC, and can be tailored for various applications, including standard, tough, flexible, clear, high-temperature, and castable resins.

“Dr. Ulven’s work is highly translatable to real-world problems,” said NDSU Interim Vice President for Research and Creative Activity Heidi Grunwald. “The market size for advances in 3D printing is projected to grow from $20 billion in 2023 to $110 billion by 2033. This is the kind of exciting, commercially viable research and development that represents NDSU’s land-grant mission.”

Additionally, they created processing approaches that use directional flow control to orient the reinforcement directionally, layer by layer, during the printing process. “With the short fiber reinforcement technology strategy, we have been able to demonstrate that non-isotropic material properties in 3D printed articles can be produced,” Ulven said.

By using short fiber reinforcement technology in 3D printing, it's possible to tailor the material's mechanical properties so that they are non-isotropic, meaning they differ depending on direction within the printed part. This is a significant achievement because most conventional polymers are isotropic, displaying uniform properties in all directions.

Short fibers dispersed inside the 3D print resin can be aligned during the extrusion and deposition process, often following the direction of printing. This directional orientation gives rise to non-isotropic properties, including higher strength in directions parallel to the fiber alignment, which mimics natural structures (such as bamboo), where fiber alignment creates directionally optimized performance.

The team has also devised techniques for incorporating continuous fibers, such as carbon, glass, and basalt, into both photocurable and reactive resins. This was achieved by designing a new nozzle geometry that allows for proper wetting and dispensing of composite materials onto the print bed just before the gelation or curing of the liquid thermoset resin, Ulven said. “The nozzle geometry and how continuous fiber reinforcement is introduced into the liquid resin contained within the nozzle are paramount to producing quality composites with good resin wet-out onto the print bed just before consolidation.”

Ulven noted that engineers are constantly looking to push the envelope in terms of the ease and efficiency of materials processing, while controlling and improving the resulting material properties in a near-net shape form for a variety of applications.

“Our progress in developing composite 3D printing approaches allows for these engineering gains,” he said. “These technologies allow 3D printer users to print structurally sound composite materials easily and efficiently that have demonstrated uses like truss sections for girders, grid sections for complex composite sandwich cores, and various cones.”

"Working on Dr. Ulven’s research in 3D printing and continuous fiber composites has been both exciting and rewarding,” said NDSU Ph.D. student Prashant Lakhemaru. “I have gained valuable insights into how fiber reinforcement can significantly enhance the strength and performance of printed materials. Our group recently focused on additive manufacturing of continuous carbon fiber-reinforced thermoset composites.”

Ulven’s work has been funded by various federal agencies over the past several years, including the U.S. Army Research Laboratory (ARL), the U.S. Army Ground Vehicle Systems Center (GVSC), and the U.S. Army Engineer Research and Development Center (ERDC).

The research Lakhemaru has been involved with focuses on the challenge of 3D printing with continuous fiber-reinforced thermoset composites. The team built a 3D printer capable of printing a special resin that can be hardened by UV light and reinforced with continuous carbon fiber. They then tested how the fiber type and its twist affected the strength of the printed parts.

“Our team is also developing machine learning–based methods for defect detection on printed surfaces, aiming to eliminate defects such as voids and irregularities that compromise mechanical performance, Lakhemaru said. “I truly enjoy being part of this work, as it combines innovation with real-world applications. Looking ahead, I see this research paving the way for advanced manufacturing solutions that can transform industries ranging from automotive and aerospace to biomedical engineering."

“Dr. Ulven’s groundbreaking research is redefining what’s possible with 3D printing,” said Alan Kallmeyer, NDSU Dean of Engineering. “By pioneering methods that integrate fiber reinforcement into printed structures, he and his team are addressing the technology’s greatest challenges of strength and durability. Their work has the potential to transform industries by enabling more efficient, sustainable, and high-performance manufacturing solutions. It’s an exciting example of the innovation happening every day at NDSU’s College of Engineering.”

Even with the discoveries in continuous fiber reinforcement, the research is not done for Ulven’s team.

“Our next step is to scale up our methods and approaches so that we can print larger structures along with the incorporation of larger fiber bundles to build up structures layer by layer faster,” Ulven said.