Spectroscopic Diagnosis Of Temperature Distribution Of Twin-Electrode Tig Coupling Arc Based On ART Algorithm

The twin-electrode TIG coupling arc is a new type non-axisymmetric welding heat source developed in recent years, which is generated by a special welding torch that has two slanting tungsten electrodes insulated from each other. And two power supplies are separately connected to the two electrodes. The shape of the coupling arc is no longer axisymmetric. The physical properties of this coupling arc are unknown. Measurements of plasma properties, such as the temperatures or the densities of species, can greatly improve the understanding and performance of the coupling arc applications. To the present little research has been reported. In this paper, the temperature distribution of the coupling arc is systematically determined by spectroscopic technique.According to the study object of a stationary coupling arc between both slanting electrodes and a water-cooled copper plate, a monochromatic imaging system is capable of acquiring two-dimensional images with a high speed camera, a neutral, and a narrow-band filter and a lens. For the purpose of acquiring coupling arc images from different directions, the welding torch can rotate around its axis from 0°to 180°.Due to the asymmetry of the coupling arc, the emission coefficient of the non-axisymmetric plasma is not only related to radial location, but also related to azimuth. Thus, the Abel inversion is not applicable to it. In this investigation, the emission coefficient of the coupling arc was reconstructed on the basis of the algebraic reconstruction technique (ART) which was programmed by matlab language. The dependence of the reconstructed quality on three configurations (four, eight, ten projected views) were presented and discussed via a displaced gaussian model in order to define optimal scheme for good quality with limited views. The results show that the four-view configuration has a high reconstructed error. The minimum error is found for the ten-view configuration due to the largest number of views. For the ten-view configuration, the emission coefficient was reconstructed with error ranging between 1% and 8%. Furthermore, the results are more accurate and noise-resistant in the center area of the arc, which is one of the most critical parts to determine, the maximum error is less than 1%.The developed ART program was used to reconstruct the emission coefficient of a coupling arc with a current of 140 each, electrode distance 1 mm and arc length 4mm. The temperature distribution of the coupling arc was determined according to the normal temperature method. The results indicate that the maximum temperature in the high temperature region is approximately 18500 K. It is in the middle of both electrodes not below the electrodes. The distribution of temperature is different from centrosymmetric shape which is the conventional shape of a single arc. It is similar to an ellipse, and the short axis of the ellipse is in the direction that both electrodes are arranged along.The dependence of the welding parameters, such as the current, the electrode distance and arc length, were investigated. Increase of the arc current is associated with an increase of the arc temperature and the extension of the temperature distribution. The electrode distance ranging between 0.5 and 2 has no distinct affect on the temperature distribution because of the smallness of the electrode distance, but it has a significant effect on the bulk temperature,with the increase of the electrode distance, the bulk temperature decreases. Arc length seldom affects the distribution of the maximum temperatures, with the increase of the arc length, the extension of temperature distribution is larger. So the influence of the arc length on the temperatures of the coupling arc is limited.