image: The research team awarded a $1 million, two-year grant to help revolutionize metal additive manufacturing includes, from left to right: Tao Sun, associate professor of mechanical engineering at Northwestern University; and Penn State faculty members Christopher Kube, associate professor of engineering science and mechanics; Andrea Argüelles, associate professor of engineering science and mechanics and of acoustics and affiliate of the Materials Research Institute; and Allison Beese, professor of materials science and engineering and of mechanical engineering.
Credit: Provided by Chris Kube
UNIVERSITY PARK, Pa. — Additive manufacturing, or 3D printing, has drastically improved the uniformity and speed of metal parts manufacturing, but the printed parts are often plagued with defects, such as pores, that limit their performance. The process also requires an inspection of each part after printing, which can slow down production and limit where parts can be made.
Christopher Kube, associate professor of engineering science and mechanics in the Penn State College of Engineering, was selected to lead a multidisciplinary team on a two-year, $1 million grant from the Structures Uniquely Resolved to Guarantee Performance (SURGE) program of the federally funded Defense Advanced Research Projects Agency (DARPA) to develop a method to detect, measure and localize porosity defects inside 3D-printed metal parts while they are being made. Instead of waiting until after printing to check for flaws, Kube’s team will develop acoustic sensors built into the printing platform and ultrasonic microphones to detect and measure pores during the print.
Penn State faculty members Allison Beese, professor of materials science and engineering and of mechanical engineering, and Andrea Argüelles, associate professor of engineering science and mechanics and of acoustics and affiliate of the Materials Research Institute, as well as Tao Sun, associate professor of mechanical engineering at Northwestern University, will serve as co-principal investigators on the grant.
In the Q&A below, Kube explained his plans for the research and its potential implications on the metal additive manufacturing industry.
Q: How will you utilize ultrasound, high speed X-ray imaging and microphones to improve metal additive manufacturing?
Kube: In laser-based metal 3D printing, a laser beam selectively melts metal powder in succession and layer-by-layer to create a 3D-printed part. Defects such as pores manifest from micron-sized bubbles formed in the laser melting process and get deposited into the solid part when the liquid melt pool solidifies.
Currently, advanced X-ray computed tomography is applied to inspect for the pores after the print, which is both costly and time-consuming. Our team recognized that the melt pools emit characteristic acoustic tones related to bubble formation in the liquid, which is a precursor to a pore. Our technique is based on stimulating the melt pools with short duration ultrasonic waves such that the bubbles “sing” to the acoustic microphones installed within the build chamber.
A unique aspect of the research is our collaboration with Sun and the Advanced Photon Source (APS) at Argonne National Laboratory. At APS, the bubbles and pores can be directly visualized with high-speed X-ray imaging. Our acoustic technique will be developed at APS, where direct high-speed X-ray images of bubbles and pores will provide the training data that will allow us to interpret the acoustic signatures when measurements are performed in printers at Penn State.
Q: How do these advancements aim to improve efficiency, quality control and reliability of 3D-printed metal parts?
Kube: There are currently no in-process sensing techniques that can reliably measure 25-micron subsurface pores and locate them to within 125 microns. Achieving these metrics enables downstream modeling of microstructure and mechanical properties like part strength to become accurate and viable. Coupled sensing and modeling is a paradigm shift from the current qualitycontrol practice. In the future, we could have print farms producing thousands of parts one day and installed into defense systems the next day. It is exciting to be part of a program that has the potential to impact supply chains, enable superior performance and make systems more sustainable.
Q: How do you plan to test the method, and where?
Kube: Our technique will be developed at Penn State and at APS. In late 2026, we will demonstrate the ability to detect, measure and locate pores in an actual print in a laser powder bed fusion 3D printer at Penn State.
Q: How does your project correspond to the SURGE program’s goals?
Kube: The DARPA SURGE program announcement was a major event for researchers conducting research in additive manufacturing. It was an honor to be selected as one of only four teams to participate in the program. DARPA is well-known for supporting high-risk, high-reward projects and, thus, presents a huge opportunity for our team and Penn State to be part of a revolution in 3D printing.
Q: How does this grant further your overall research program at Penn State?
Kube: This grant continues strong multi-disciplinary collaborations between the Kube, Beese, Argüelles and Sun research groups, which is at the intersection of advanced manufacturing, material science, acoustics and synchrotron X-ray research. Research in this area has been incredibly rewarding because of the multidisciplinary teams it demands and harbors.