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Marriage of Laser/Arc Welding Promises More for Less

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Lawrence Normie

HAIFA, Israel -- Plasma-Laser Technologies (PLT) Ltd. has coupled arc plasma and a laser beam to produce a cutting and welding tool that offers more than just the sum of the two systems.
The notion of augmenting a laser beam with a plasma arc for welding has been around since the late 1980s. Until recently, devices consisted of separate laser and plasma heads directed at the point of work. One advantage of these hybrid systems is enhanced welding speeds of 1.5 to 4 times that of conventional plasma welding systems. In the past, however, these improvements came at the cost of high laser power outputs (up to 250 kW) and arc currents approaching 300 A.
More recently, attempts have been made to improve the efficiency of the combined laser-plasma process by means of a collinear arrangement where the laser beam is propagated through the plasma arc.

Efficient welding
The secret to PLT's Laser Plasmotron is that a portion of the laser energy propagating through the plasma is absorbed and coupled into the plasma arc before it reaches the work surface. Company officials say the collinear laser-plasma arc welding head produces several beneficial effects: increased plasma temperature and electroconductivity along the laser axis; a constriction of the plasma arc and a resultant increase in the plasma energy density; greater dynamic pressure at the weld; and increased rigidity of the arc.
Also, because the plasma head nozzle constricts the gases, a relatively small part of the laser beam power is lost to the plasma during transmission. These combined effects cause the arc to become more like a laser than an arc, according to company officials.
PLT has developed two heads that combine a plasma arc with either a CO2 or an Nd:YAG laser. Tests show that a 1-kW Nd:YAG laser with focal spot diameter of 0.67 mm, collinearly combined with a plasma arc, achieved the equivalent welding performance of a 2-kW stand-alone laser. This increases the life of arc electrodes while reducing consumption of welding gas and electrical energy. Also, welded joints are clean, a condition usually obtained with laser-only welding systems.
Potential commercial applications include the automotive, shipbuilding, aerospace and offshore sectors. The device was developed with an industrial R&D grant from Israel's Ministry of Industry and Trade.

Photonics Spectra
Sep 1997
industrialResearch & TechnologyTech Pulse

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