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April 11, 2022

A penetrating gaze: System allows world’s first X-ray look at electron-beam 3D-printing process

Written By: Renee Meiller


One of the greatest areas of potential for 3D printing might be in the ability to realize geometrically challenging or one-of-a-kind designs—for example, a patient’s replacement scapula, designed from a scan of the original bone, or strong, lightweight components of a system that traveled to Mars for sampling the planet’s rocks and soil.

In cases such as these—in which each complex metal part was printed using an additive manufacturing technology known as electron beam powder bed fusion—failure due to defects hidden deep within the parts is not an option. Yet because of a lack of understanding of that printing process, those hidden defects still very much exist.

Now, a team of mechanical engineers at the University of Wisconsin-Madison has pioneered the world’s first system for concurrently using synchrotron X-ray imaging and diffraction, with complementary thermal and visible light imaging, to fully study the electron beam powder bed fusion process in real time.

Led by Mechanical Engineering Assistant Professor Lianyi Chen, this integrated system is a major step forward in researchers’ understanding of the fundamental mechanisms underlying this unique 3D printing process, which previously has been limited to what they could see on the surface of the printed materials.

Lianyi Chen, Charles Ringrose Assistant Professor of Mechanical Engineering

That’s key to a future with defect-free parts—in particular, high-end parts that can withstand harsh environments. “For electron beam powder bed fusion, right now, there’s pretty fast growth,” says Chen. “It’s an important technology to make parts for aerospace—for example, for jet engines, with titanium aluminide. We can’t make these with any other 3D-printing technology.”

The team completed its system in early January 2022 and has already tested it successfully on the Advanced Photon Source, an ultra-bright, high-energy synchrotron X-ray user facility at Argonne National Laboratory. “It is the first time we have the ability to see what happens beneath the surface—what are the defect formation mechanisms,” says Chen. “With a deeper understanding of the process, we can design better technology to move the process to a much higher level.”

Like an X-ray of the human body, the high-energy synchrotron X-ray enables the researchers to see, in unprecedented detail, how the material is behaving within the entire part—as it’s printing. A thermal camera on the researchers’ system allows them to study how the temperature evolves during the process, while a visible light camera enables them to study the part’s evolving surface morphology. “It is quite fascinating,” says Luis Izet Escano, the mechanical engineering PhD student in Chen’s group who led development of the system. “With only one run on our machine, we are able to see several aspects of the printing process simultaneously.”

In a nutshell, electron beam powder bed fusion begins with a base of metal powder on a substrate; an electron beam then melts and fuses additional powder layers to construct a part from the bottom up. While the process sounds straightforward, there actually are lots of physical phenomena at play—and today’s commercial printers aren’t built for gathering data like that from the synchrotron facility. That’s why Escano and his colleagues designed and fabricated their system from scratch.

For its design, the group drew on its extensive experience building tools that allow them to use a synchrotron to study and improve another additive manufacturing technology called laser powder bed fusion.

The team also overcame several technical challenges associated with studying the electron beam powder bed fusion process—among them, maintaining the high vacuum needed for the process, mitigating vibrations from the vacuum pump in their measurements, and manufacturing special viewports so that the synchrotron’s X-rays could pass through them effectively.

The result is not only the world’s first window into the electron beam powder bed fusion printing process, but also its most versatile. “Development and integration of the system has been a great challenge, as it requires expertise in multiple engineering areas,” says Escano. “Now, the flexibility of our machine allows us to run experiments and collect data quite fast—and this will accelerate our research toward the fundamental understanding and perfection of this printing technology.”

Chen is the Charles Ringrose Assistant Professor and a fellow of the UW-Madison Grainger Institute for Engineering. Graduate students in his group who also contributed to the system’s development include Xinhang Zhang, Qilin Guo, William Dong and Minglei Qu. Samuel J. Clark and Kamel Fezzaa, who are beamline scientists at the Advanced Photon Source, assisted with the group’s synchrotron X-ray experiments. Funding for the work came from the National Institute of Standards and Technology and Chen’s faculty startup package at UW-Madison.

Photo caption: Preventing defects in 3D-printed parts requires understanding the process. To learn more about a nascent metal-printing process known as electron beam powder bed fusion, a team of UW-Madison mechanical engineers, led by assistant professor Lianyi Chen, pioneered a system that allows them to use synchrotron X-rays to view virtually all aspects of it—including inside the part being printed—in real time. PhD student Luis Izet Escano (pictured), whose advisor is Mechanical Engineering Assistant Professor Lianyi Chen, led development of the system.