"COLD" LASER BEAM IMPROVES ARC WELDING, SAVES MONEY
COLUMBUS, Ohio - While arc welding has been used for decades to join metal parts on everything from cars to boats to airplanes, the basic technology behind this multi-billion dollar industry has changed little since World War II.
Now, engineers at Ohio State University have devised a way to improve the precision of arc welding, and even to help manufacturers save energy and equipment costs.
Traditional arc welding is hard to control and sometimes damages metal parts, Albright said. More precise welding is now done with expensive multi-kilowatt lasers in the automobile and aerospace industries. The LAAW laser uses only seven watts -- little more than a Christmas tree light bulb.
Albright thinks that once the technology is commercialized, a LAAW system could cost one tenth of what today's typical laser welding systems cost.
"Just to improve our control over arc welding -- that would be worthwhile in itself," Albright said. "But with further development, LAAW could eventually enable us to weld materials with the same high precision as we can direct a laser beam."
Albright's co-inventors at Ohio State include J. William Rich, professor of mechanical engineering, and Walter Lempert, associate professor of chemistry and mechanical engineering. They partnered with Richard Miles, professor of mechanical and aerospace engineering, and Sergy Macheret, a research scientist, both of Princeton University.
Arc welding is popular in industry because it creates very strong material connections. With this technique, powerful electrical arcs -- unruly streams of electric current akin to mini lightning bolts -- melt metals at temperatures as high as 3500°C.
Arcs can move unpredictably, Albright said, and sometimes they warp welded parts or splatter liquid metal. "Ever wonder why lightning looks so jagged?" he asked. "When you start an arc, initially there's no telling where it's going to go." Welding arcs, like lightning bolts, tend to follow the path of least electrical resistance, Lempert added.
Since the late 1970's, researchers have known that laser beams could be used to create a path of electrons for arcs to follow. But generating enough electrons to attract a welding arc always required a high-power laser, and a high-temperature laser beam path.
A one-kilowatt laser, for instance, concentrates the power of a small space heater into a single, sub-millimeter size spot. Such lasers are often used to manufacture electronics, because they generate enough heat to melt thin metal parts in very small, controlled areas.
The Ohio State and Princeton engineers came up with a technique for creating an electron path with much more finesse than brute force: They infused small amounts of carbon monoxide gas into a welding gas, then used a low-power laser at just the right frequency to cause molecules of the gas to vibrate. The laser beam cut a glowing blue trail through the weld chamber as the vibrating carbon monoxide molecules shed their electrons, creating an attractive path for the welding arc to follow at low temperatures. Since very little energy is required in this process, very low power lasers can be used. The engineers dubbed this effect "cold ionization" because it charged, or "ionized," the carbon monoxide gas without generating heat.
When the engineers turned on the welding arc, it immediately jumped to the laser beam. First the engineers aimed the laser at the head of a bolt they'd placed in the weld chamber, then to a sheet of stainless steel. The arc followed the beam each time, creating welds in the metal.
Albright and his colleagues are now looking for a commercial partner to help them develop LAAW. Once commercialized, the LAAW system could save manufacturers money in a couple different ways, Albright said. First, the cost of electricity around the U.S. varies between seven cents and 15 cents per kilowatt-hour, so large manufacturing operations could save money if they used lasers that required less power.
But the real payoff of using the LAAW system would likely come from lower equipment costs, he said. A typical multi-kilowatt industrial laser costs between $200,000 and $300,000.
"We're hoping that, one day, with a $5,000 power supply and a $20,000 laser, we could do the work of a laser system costing ten times as much," Albright said.
This work was supported by AGA Gas, Inc., a maker of welding gas and equipment, headquartered in Cleveland.