Spectrum analysis of the arc for laser-guided robot welding applications

In robot arc welding applications, in order to overcome inaccuracies of the robot itself and the workpiece, the tracking of the seam is of primal importance. To detect the seam, a novel sensor based on a laser scanner and using triangulation methods has been developed. A definite problem of the development is the difference in the optical power emitted by the arc which is in the range of hundreds of Watts and the power of the diode laser in the range of mW. In order to achieve good signal to noise ratio, it is necessary to select a wavelength where the glow of the arc is minimal and design an appropriate interference filter. For this purpose detailed measurements and analysis of the spectrum of the welding arc have been performed. The measurements extend for the UV region of the spectrum to the near IR region. The study was concentrated on the welding of ferrous metals using as shielding gas a mixture of 80 percent Ar and 20 percent CO2 and welding currents in the range of 100A to 160A. The measurements have revealed the presence of many strong emission lines in the spectrum.