Engineers at the Ohio State University may have changed the future of welding and the automobile industry. For years, auto manufacturers have sought ways to improve vehicle safety and efficiency by pioneering new metals and techniques to lighten and strengthen their products. Some of you may recall the stir created when Ford introduced its aluminum bodied F-150. The redesigned truck was lighter, faster and more fuel efficient, but required Ford to establish training programs for their repair facilities because of the complexities involved in bonding aluminum to other metals. “Materials have gotten stronger, but welds haven’t. We can design metals with intricate microstructures, but we destroy the microstructure when we weld,” said Glenn Daehn, Professor of Materials Science and Engineering at Ohio State.
Ohio State’s new welding process is called vaporized foil actuator welding (VFAW). With VFAW, the difficulties that come from using lighter, more advanced metals like aluminum may soon be a thing of the past. Although the name is intimidating, the process is surprisingly simple. VFAW is a solid-state collision process like explosion welding. In explosion welding, a controlled explosion hurls a movable workpiece against a stationary workpiece at a velocity great enough to create a metallic bond between them when they collide. VFAW is based on the same principle, only at a much more reduced and manageable scale.
In laboratory experiments, researchers place a thin sheet of aluminum foil, called the vaporizing foil actuator, onto a solid block of steel. This is followed by a piece of electrical insulation and a flyer. The flyer is the workpiece that will be launched against the stationary workpiece above it. Next, the researchers place two plastic standoff sheets on either side of the flyer. This provides the space necessary for the flyer to be propelled against the stationary workpiece. Then, the stationary workpiece, called the target plate, is placed on top of the plastic standoff sheets. Finally, the whole stack is capped with another solid block of steel.
This set-up is connected to a high-voltage capacitor bank. When triggered, the capacitor delivers a very brief electrical pulse to the thin piece of aluminum foil. Within microseconds, the current vaporizes the foil, skipping the liquid state and immediately turning the foil into a burst of hot gas that OSU engineers refer to as “foil plasma.” The force of the rapidly expanding gas slams the flyer against the target plate at speeds approaching hundreds of meters per second. As a result, the atoms of the flyer bond to the atoms of the target plate without ever melting. The strength of the bond becomes evident under the microscope. In one microscopic view, you can see tendrils from a piece of titanium extending outward and “gripping” the piece of copper to which it has been fused. Check out this video for a closer look at the process.
Studies conducted so far show that the new welding process could revolutionize the auto industry’s weld quality and limit its environmental impact. VFAW uses 80 percent less energy than spot welding thanks to its reliance on short, high-voltage bursts instead of constant power sources. The process also creates deep molecular bonds that are about 50 percent stronger than resistance spot welds. Moreover, the VFAW process can be used to join the types of metals that manufacturers have until now been forced to pass over because of the difficulty, or impossibility, of getting those metals to bond. These include different combinations of copper, aluminum, magnesium, iron, nickel and titanium. Researchers have even used the process to produce strong bonds between commercial steel and aluminum alloys. The technique is also powerful enough to shape metal parts at the same time it welds them together, saving manufacturers a step that could have major impacts in auto-manufacturing efficiency. “With our method, materials are shaped and bonded together at the same time, and they actually get stronger,” said Daehn. Daehn and his team now plan to join with manufacturers to further develop the technology, which will be licensed through Ohio State’s Technology Commercialization Office.
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