# Spectroscopic Approach for the On-Line Monitoring of Welding of Tanker Trucks
## 4 Conclusions  
In this paper, we have presented an analysis associated with an on-line monitoring system designed and implemented for an arc-welding process employed in the manufacturing of tanker trucks. The system is based on plasma optical spectroscopy, although it also allows the acquisition of welding current, voltage, process and wire feed speed and protection gas flow rate information. The information provided by the plasma spectra of the welding process supports good performance in terms of its ability to detect different defective situations that may appear during the welding of Al-Mg alloys. Weld trials were designed and carried out to test the performance of the system by provoking different perturbations to the process. In addition, extensive in-line production validation has also been performed, verifying the obtained results with the X-ray inspection required by the associated standard. This point is highly relevant, as it allows a realistic test and validation of the monitoring system within a completely real production scenario, avoiding the uncertainties associated with the use of simulated defects. It has been demonstrated in production that the H I profile is a good parameter to evaluate atmospheric contamination in the process or contamination due to a lack of cleanliness and, therefore, the occurrence of porosities. In fact, the generation of these H I profiles against different H I lines or other averaged groups of lines (e.g., Al I) may give  
Figure 8: Output monitoring profiles for Tanker #2, seams 215712, 221219 and 222940. (**a**) Ratio of Mg I (553 nm) to an average of the Mg lines profile for the three seams. (**b**) Ratio of H I (656 nm) to an average of the Al I lines profile for the three seams. rise to profiles with improved features in terms of sensitivity or noise. The ability of other species, such as Ar I, Mg I or Na I, to detect other defects such as cracks that do not appear in H profiles has also been discussed. In this regard, it is also worth mentioning that our studies suggest that there are other porosities that appear in isolation whose causes are probably different from those of porosities that appear in groups, as they are not reflected in the H profiles. The results derived from the employment of Na lines should be carefully studied, although the correlation of the perturbations in these profiles with the appearance of porosities is quite evident. We have performed different studies, for example, analyses via LIBS (laser-induced breakdown spectroscopy) of the composition of all the elements involved in the welding process: plates, wire feed, tools used to prepare the joint, and so on. We have detected the participation of Na both in the wire feed and in the plates and it is known that during the manufacturing of some Al-Mg alloys the plates are cleaned with compounds containing Na. Deposition of environmental pollutants in stored raw materials can be another source of contamination [30]. In fact, recent preliminary studies performed by our group suggest that some elements not typically employed in spectroscopic analysis (Li, Na, K) may indicate contamination and can therefore be used to detect some specific weld defects. More studies will be needed to correlate Na profiles and the mentioned elements with seam contamination and final welding quality. The ultimate goal of this kind of monitoring system should be not only to offer real-time information about the process but also to help in discovering the causes underlying the appearance of defects. The proposed solution might prove useful in this regard, for example, by controlling ambient temperature and humidity or protecting the gas flow rate and establishing a correlation with the H profiles and the porosities detected in the X-ray inspection. Apart from extending the study to further tanker production processes, future works might be focused on adding more relevant sensors to the system.