ABSTRACT This work describes exploratory experimental procedures implemented for the development of a non-intrusive and real-time sensor for weld defect tracking which uses emission spectrometry for measuring the electromagnetic content of the plasma-weld pool interface in the GMA welding arc. The welding process monitoring is carried out by calculating the Iron (Fe) and the Manganese (Mn) electronic temperatures within the welding arc column, admitting that the observed region is at local thermodynamic equilibrium. The temperature was calculated by utilizing the relative intensity method, which is based on the Boltzmann and the Saha Laws and on the definition of the emission line intensity. The calculated electronic temperatures of the two elements were correlated with the position of welding defects, which have been introduced for simulation purposes. These simulated defects resulted in abrupt changes in the average temperature values, thus providing an indication of the presence of a defect.
INTRODUCTION For many years, several different monitoring techniques have been studied, attempting to develop a general technique capable of dealing with the inherent complexity of the arc welding processes. Such studies aimed mainly at developing methods of on-line controlling the quality of the welds in order to prevent the need for the costly and time consuming post weld inspection processes. The innovations generated by these studies are based on the physical phenomena involved in the arc welding processes, mainly those related to the plasma arc and its influence on the weld pool (Degout, D., 1986). The applied techniques range from numerical simulation of the arc (Haidar, J., 1996), image analysis (Kim, W., 1987), sound spectrum analysis and electromagnetic emission analysis (Lacroix, D., 1999), (Ancona, A., 2001), (Sforza, P., 2002) to the use of intelligent systems, based on neural networks and fuzzy logic (Moon H.S., 1996).