Laser Enables Precision Arc Welding

Kevin Robinson

Welding is big business. Approximately $2 billion and $600 million are spent annually on arc welding and laser welding equipment, respectively. Now researchers at Ohio State University have demonstrated a technique that could revolutionize the field by reducing the cost of precision industrial welding systems by 90 percent. The technique uses a laser to create a path of ionized molecules across which an arc prefers to jump.

In arc welding, a high-amp current passes between two electrodes, creating a spark that melts metals together, but it is difficult to control the position of these arcs. Laser welding, in contrast, is precise but expensive: With a price tag of about $300,000, an industrial laser welding system is 50 to 60 times more costly than a similar arc system.

The research group, led by Charles E. Albright, a professor of industrial, welding and systems engineering, and Walter Lempert, an associate professor of chemistry and mechanical engineering, has demonstrated what it calls the laser-assisted arc welding process, a low-power laser technique that combines the best of both approaches. Albright said the work began when Bill Rich, also of the university, showed him that shining a CO laser through a chamber of carbon monoxide gas created a blue glowing path of ionized molecules. Albright decided to find out if a high-power electrical arc would form along the ionized gas, taking the path of least resistance, as if the ionized gas were a thin wire.

His team used a 7-W CO laser in an experimental welding chamber filled with argon gas and 1 percent carbon monoxide. The laser produced the ionized path, and an arc jumped along that path. The researchers have directed test welds to the head of a stainless steel bolt with the technique.

Other researchers had exhibited the phenomenon previously, but their setups required 1-kW lasers that create ionized paths by heating plumes of high-temperature material. The new process uses cold ionization, wherein the laser affects only the vibrational energy levels of the molecular gas, and thus requires a much less powerful laser source.

Looking for backing

Albright estimated that the laser and an electric arc power supply would cost roughly $35,000, a tenth of the cost of today's precision laser welding systems. With more testing, he expects the technique to work well with pulsed arc welding, and a similar system might be used to cut steel. He also hopes to control a continuous arc with the system.

The scientists are searching for a sponsor who will fund large-scale research into the technique. Until then, they are carrying out related work. For example, Albright said that although the CO laser is reliable and relatively inexpensive, they are investigating other molecules with which other lasers will work. "We would like to find molecules that would work in the 600-nm to 1-µm range, where we could look at a diode laser to excite them," he explained. This would bring down the cost of the system even further.