Vaporized Foil Actuator Welding technique from OSU uses 80% less energy and delivers bonds 50% stronger; joining dissimilar materials
30 October 2015
Engineers at The Ohio State University have developed a new welding technique—Vaporized Foil Actuator Welding (VFAW)—that consumes 80% less energy than a common welding technique, yet creates bonds that are 50% stronger. The new technique could have a significant impact on the auto industry, which is poised to offer new cars which combine traditional heavy steel parts with lighter, alternative metals to reduce vehicle weight.
Glenn Daehn, professor of materials science and engineering at Ohio State, who helped develop the new technique, explained the new process in a keynote address at the recent Materials Science & Technology 2015 meeting. The Materials Science & Engineering annual meeting is organized by the American Ceramic Society, the Association for Iron & Steel Technology, ASM International, and the Minerals, Metals & Materials Society.
Despite recent advances in materials design, alternative metals still pose a challenge to manufacturers in practice. Many are considered un-weldable by traditional means, in part because high heat and re-solidification weaken them, said Daehn.
Materials have gotten stronger, but welds haven’t. We can design metals with intricate microstructures, but we destroy the microstructure when we weld.
—Professor Daehn
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| A diagram showing vaporized foil actuator welding, a technique developed at The Ohio State University. Image by Glenn Daehn, courtesy of The Ohio State University. Click to enlarge. |
In commonly used resistance spot welding, manufacturers pass a high electrical current through pieces of metal, so that the metals’ natural electrical resistance generates heat that partially melts them together and forms a weld. However, generating high currents consumes a great deal of energy, and the melted portions of metal are never as strong afterward as they were before.
Over the last decade, Daehn and his team have been trying to find ways around those problems. They’ve amassed more than half a dozen patents on a system called vaporized foil actuator welding.
The basic premise of VFAW is that when the energy deposition rate is very high, a thin conductor can be heated far above its energy of sublimation due to the constraint of inertial and magnetic forces. When these inertial forces let go, the conductor vaporizes and the stored energy is released as a pressure pulse. This pulse can push two metals together, bonding them.
In VFAW, a high-voltage capacitor bank creates a very short electrical pulse inside a thin piece of aluminum foil. Within microseconds, the foil vaporizes and a burst of hot gas pushes two pieces of metal together at speeds approaching thousands of miles per hour.
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| Top: Microscope view of copper (top) welded to titanium (bottom) using VFA. Bottom: Microscope view of steel (top) welded to aluminum alloy (bottom) using VFA. Images by Glenn Daehn, courtesy of The Ohio State University. Click to enlarge. |
The pieces don’t melt, so there’s no seam of weakened metal between them. Instead, the impact directly bonds the atoms of one metal to atoms of the other. Seen under a high-powered microscope, the bond often features delicate curlicues in spots where veins of both materials extend outward and wrap around each other.
The collision-welding technique uses less energy because the electrical pulse is so short, and because the energy required to vaporize the foil is less than what would be required to melt the metal parts.
So far, the OSU engineers have successfully bonded different combinations of copper, aluminum, magnesium, iron, nickel and titanium. They have created strong bonds between commercial steel and aluminum alloys; high-strength steel and aluminum join together with weld regions that are stronger than the base metals.
The technique is powerful enough to shape metal parts at the same time it welds them together, saving manufacturers a step.
Daehn and his team now want to join with manufacturers to further develop the technology, which will be licensed through Ohio State’s Technology Commercialization Office.
This project is funded by the Department of Energy and the National Science Foundation (NSF), and was one of the first to participate in I-Corps@Ohio, a new collaboration modeled after and approved by NSF’s successful I-Corps commercialization program. Ohio is the first to have a statewide collaboration that is based on the NSF model, yet fully funded by the state. The program is funded and supported by the Ohio Department of Higher Education.
Resources
Glenn S. Daehn and Anupam Vivek (2015) “Collision Welding of Dissimilar Materials by Vaporizing Foil Actuator: A Breakthrough Technology for Dissimilar Materials Joining” DOE Annual Merit Review 2015
Anupam Vivek, Glenn S. Daehn (2014) “Vaporizing Foil Actuator: A Versatile Tool for High Energy-rate Metal Working,” Procedia Engineering, Volume 81, Pages 2129-2134 doi: 10.1016/j.proeng.2014.10.297
Vivek, A., Hansen, S. R., Liu, B. C., & Daehn, G. S. (2013) “Vaporizing foil actuator: A tool for collision welding” Journal of Materials Processing Technology, 213 (12), 2304-2311 doi: 10.1016/j.jmatprotec.2013.07.006
A good technique for steel to aluminium bonds would be very useful. Reducing weight (mass) while maintaining strength is good no matter what powertrain you use.
Posted by: mahonj | 31 October 2015 at 05:07 AM
What happens to the atoms in the aluminium foil?
Where does the vaporized (sublimated) aluminium go?
Those ESM photos show some pretty convincing metal bonds!
Posted by: Thomas Pedersen | 03 November 2015 at 06:45 AM
The atoms will be partially oxidized and will cling to surrounding materials but are small in quantities. It is expanded gas which makes up most of the bonding force.
Explosive bonding with more standard explosives is well known. ..HG..
Posted by: Henry Gibson | 04 November 2015 at 02:23 PM
The field of inquiry this actually belongs to is brazing, not welding, because two dissimilar materials are bonded. This really looks OK for weldments that represent large surfaces like pipe joints, not really fastener designed parts, such as bumpers.
Posted by: kalendjay | 12 November 2015 at 02:27 PM