3D printing, also known as additive manufacturing, is thought to be a completely disruptive technology that will upend traditional processes in the world of manufacturing.
The technology allows engineers to actually print a metal part (for example, a piece of a car engine) layer-by-layer, rather than machining the part out of a large, solid block. The process has a laundry list of benefits – think cheaper, faster, lighter, more customized, better designs and less waste.
Despite metal 3D printing’s novel process and innovative design parameters, one aspect of the technology remains conventional – the materials. Currently used materials, such as the common titanium alloy Ti-6Al-4V, were designed and optimized decades ago for traditional manufacturing approaches. Manufacturers, however, are pushing for the creation of new materials so that they can use metal powders designed for 3D printing and its high cooling rates.
The Challenge
Currently, designing a new alloy means a lot of time and a lot of money.
“It’s very hard to develop new materials for additive manufacturing, because evaluating new alloys requires lot of powder. At least 100 pounds of powder would be needed per composition in order to test all the process variables related to that material. This is both expensive and time-consuming,” explained Bryan Webler, assistant professor of materials science and engineering at Carnegie Mellon University (CMU). “Even at a research scale, it’s not straightforward or efficient to fabricate small batches of powder for every possible material composition that we need to test. We need computational and experimental approaches to screen compositions to provide some initial guidance before we try to make test batches of powders.”
Alternative Approach
Researchers at CMU’s College of Engineering are addressing the experimental approach to composition screening by using solid material instead of powder. Webler can produce small metal buttons via arc-melting of virtually any composition. Up to 16 of these buttons can be placed in a 3D-printing machine to make tracks and pads of remelted material on each button over a range of process variables (e.g., beam power and travel speed). After characterizing the melt pools, initial insights can be gained into how that alloy reacts to the fast solidification rates of 3D printing.
“This screening method allows us to change alloy composition and additive process variables in a way that lets us more quickly understand and develop correlations between process variables and alloy composition,” Webler said.
Webler, a member of the NextManufacturing Center at CMU, is collaborating with the center’s co-directors, Jack Beuth and Anthony Rollett, on this project. Although the project is in its early stages, it builds on a strong foundation of research in process-variable development and in the role of powders in 3D printing from Beuth, a professor of mechanical engineering, and Rollett, a professor of materials science and engineering.
Material System: Titanium-Boron
Webler chose titanium-boron as the first material system to screen with this new method to act as a proof of concept for the technology, and it has worked well for the research team. They have successfully completed initial characterization of microstructure with promising data. Corrosion testing is planned next.
Adding boron to titanium could create a lightweight and high-strength material that performs better under high-temperature conditions than the standard titanium alloys.
“The system we are working with now, titanium-boron, is very interesting. We can use additive to control the dispersion of boride particles in the matrix of the titanium-alloy material,” Webler said. “The screening method then will allow us to look at different alloys with various boron amounts and try to see which one has the most potential for a uniform dispersion of boron particles.”
Next Steps
Although Webler is now testing out the method with titanium-boron, he plans to move on to other alloys in the future. The screening system is designed to work with any alloy type. Webler, who has a background in steel research and is a member of CMU’s Center for Iron and Steelmaking, has his sights set on developing new steel alloys for 3D printing.
“The versatility of steel is enticing for additive,” Webler said. “As additive technology becomes more and more widely used, I think you’ll see more efforts to try to apply this manufacturing process to steel. There are many steel parts (particularly tool steels) that are very difficult to machine traditionally because of their complex shapes. And complex shapes are what additive does best, right?”
This research was presented at the 2017 RAPID + TCT Conference in Pittsburgh, Pa., in May. For more information on this research, please visit the NextManufacturing website (www.engineering.cmu.edu/next/index.html).
For more information: Contact Hannah Diorio-Toth, communications manager, Carnegie Mellon University, College of Engineering, Pittsburgh, Pa.; tel: 412-268-1208; e-mail: hdiorio@andrew.cmu.edu; web:www.engineering.cmu.edu
