A hybrid laser-assisted oxygen cutting technology has been developed and put into production at Bender Shipbuilding, Mobile, Ala. Mild steel plate of 1- to 2-inch thickness is being cut with a system using a CO2 laser head generating less than 2 kW of power.
The LASOX cutting head uses a laser beam to preheat and control the oxygen cutting process.
"A year ago," said Bender's R&D manager Pat Cahill, "cutting steel thicker than 50 mm would have been unheard of with a 2-kW laser. This process has the potential to cut steel plates as thick as 100 mm.
"This development opens the possibility of a new generation of steel ships that are stronger and cheaper to build."
The technology, dubbed "LASOX" by BOC Gases, the industrial gases company that pioneered the process, uses a cutting head with a laser beam directed through the center of a gas nozzle. The laser beam provides preheating of the steel workpiece to ignition temperature, and a high-speed oxygen jet targeted at the beam's footprint oxidizes the steel in a narrow cut. The head is mechanically moved relative to the plate, and the workpiece is severed as the force of a supersonic stream of oxygen expels molten metal and metal oxides from the kerf.
A part cut with the LASOX process from 1.5-in.-thick mild steel at Bender Shipbuilding.
Unlike oxyfuel cutting, no fuel is used to preheat the reaction zone. In a matter of a second or two, the laser power of the cutting head heats the targeted footprint on the workpiece to more than 900C. The laser power itself is insufficient to cut the plate; in fact, if it were more powerful, it would cause melting that would reduce the efficiency of the desired oxidative reaction. The laser beam is optically defocused to provide just enough power to create and maintain ignition temperature over the whole gas jet interaction zone.
"You've got to have a nice, round laser spot and fire the oxygen right at the bulls-eye in the middle of that spot," said Duncan Yates, technical manager at BOC's U.K.-based Fabrication Technology Center. That's where the process was first developed by BOC's Dr. Jack Gabzdyl in the 1990s in conjunction with Dr. Bill O'Neill of Liverpool University.
At Bender, the development of the technology into a commercially applied process was aided by Alabama Laser Systems (ALS), which developed the software to control the interaction of the laser beam power and the oxygen flow with programmed operation of a specialized cutting table. (Conventional laser beam cutting tables are not equipped to support
2-inch steel slabs.) The result is a technology that pierces 1.5-inch steel plate in about one second, and continues the cutting at a rate of 8 inches per minute, with a kerf of just a few millimeters.
Schematic diagram and photograph of the LASOX cutting process, in which a laser beam mounted coaxially in a high-velocity oxygen stream preheats the workpiece to enable precise cutting.
Compared with oxyfuel cutting, LASOX saves an average of 40 minutes of processing time per plate, so short runs are more economical. The standoff distance
for the cutting head is up to 7 mm, much farther than the 0.5 to 2 mm
nozzle-to-workpiece distance typical of standard laser cutting, diminishing the problem of ejected materials interfering with the head.
"I am amazed at the cut quality on the parts produced by LASOX," said Bob Lewis, general manager of Bender's metal processing facility. "Because of the cut edge surface quality, minimal heat-affected zone, and ability to hold very high tolerances, many post-cutting machining operations can be eliminated."
Gerry O'Connor, vice president and general manager of BOC's North American Industrial Products unit in Murray Hill. N.J., says the technology is being developed as a "bolt-on turbocharger" for existing laser beam cutting setups.
Schematic diagram and photograph of the LASOX cutting process, in which a laser beam mounted coaxially in a high-velocity oxygen stream preheats the workpiece to enable precise cutting.
"If you want to cut 11Z2-inch plate with your laser, just bolt a turbocharger head on. You'd never hope to cut that with a conventional laser," he said.
The project at Bender was funded through the National Shipbuilding Research
Program, a collaboration of 11 U.S. shipyards, with sponsorship from the Naval Sea Systems Command.
Other team members who are working with BOC and ALS on-site at Bender are Caterpillar and General Dynamics Electric Boat, which are expected to incorporate the next version of LASOX technology into manufacturing of mining equipment and submarines, respectively.
A short run of thick-plate parts cut from a mild-steel slab.
The team recently demonstrated bevel-cutting of steel plate with the system and are working to develop it further by adjusting to the effects of gravity induced by tilting the cutting head.
"It doesn't take an Einstein to see that this will allow better, cheaper parts in both military and civilian new builds and may revolutionize certain types of plate cutting," Lewis said. "This is some of the best plate cutting I've seen in my 37 years in the business."
ROSS HANCOCK (rhancock@aws.org) is Associate Editor of the Welding Journal.
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