The identification and intensity estimation of some aluminium emission lines have been proposed to perform an on-line quantification of the Al contribution to the laser-welding process of Usibor blanks. This boron steel is protected by an Al-Si coating that is removed by laser ablation before welding. If this process fails to remove Al from the joint surface, its contribution may affect the final properties of the resulting seams, therefore compromising their quality. Experimental tests have been performed, some of them in a real production scenario. They have been analysed and compared to the results of welding test specimens, analysis of the associated tensile properties and fracture locations and seam macrographs. These studies have indicated that on-line quantification of the Al contribution to the process is feasible and that a correlation can be established between the Al content estimated in real-time and the results derived from the off-line tests considered.The authors would like to thank the staff of Autotech Engineering and Solblank (both Gestamp companies) for their valuable help during the design, implementation and test of the monitoring system. This work has been supported by the project TEC2013- 47264-C2-1-

In this paper, an analysis on the suitability of employing a colorimetric analysis of the acquired plasma spectra to perform on-line arc-welding quality monitoring will be discussed. Different colorimetric parameters like the color temperature or the parameters associated with the hue, saturation, luminance color space will be evaluated in comparison with the standard approach based on the estimation of the plasma electronic temperature. This approach does not require the identification of the emission lines involved in the analysis, thus giving rise to a more efficient solution in terms of computational efficiency, and avoiding unambiguous identifications that may give rise to incorrect results. In particular, experimental tests performed with a tungsten inert gas arc-welding process will show the feasibility of using the proposed solution and its ability to perform an online detection of different welding perturbations.

The appearance of defects during the manufacture of tanker trucks via arc-welding is a significant problem in the industry. A reliable low-cost and non-destructive on-line method could aid the discovery of solutions to overcome productivity problems. Plasma optical spectroscopy was employed in this study to correlate the presence of several elemental emission lines with certain quality-related events, such as the appearance of porosities. Results obtained through field trials and also during in-line production show that the convenient processing of acquired process signals facilitates not only the detection of defects, but also the identification of their causes. Output monitoring signals have been compared with X-ray inspections of the seam welds performed. It has been demonstrated that the spectroscopic monitoring variables obtained are good indicators for evaluating contamination in the process and therefore the occurrence of welding defects.

In this paper an analysis on the suitability of employing a colorimetric analysis of the acquired plasma spectra to perform online arc-welding quality monitoring will be discussed. Different colorimetric parameters like the color temperature will be evaluated in comparison to the standard approach based on the estimation of the plasma electronic temperature. In particular, experimental tests performed with a TIG arc-welding process will show that some colorimetric parameters exhibit a better response in terms of detection and correlation to some defects than the traditional spectroscopic approach.