Shielded gas arc welding is an indispensable technology for joining all kinds of metals. In order to guarantee, that those processes fulfill high requirements for modern industrial applications, they take advantage of e.g. specific gas compositions or transient current phenomena for production of reliable welding joints. However, for a stable and safe process operation a profound understanding of the physics taking place in the arc plasma is needed. The level of knowledge for basic welding processes in stationary operating conditions has advanced in the past years. Yet, there is still a high demand for diagnostic techniques, which are able to resolve transient phenomena and measure parameters of plasmas containing gas mixtures or metal vapor. In this work two plasma spectroscopy techniques, Thomson scattering and Stark broadening, have been applied for the investigation of plasma parameters in stationary as well as transient welding processes operated with different shielding gas mixtures and in the presence of metal vapor. Thomson scattering uses scattering of the laser radiation by the free electrons in a plasma to provide information about their electron temperature and density. At first, it has been set up for the investigation of stationary gas tungsten arc welding (GTAW) processes with inert and molecular shielding gas mixtures. Thereafter, this technique has been extended for application to pulsed gas metal arc welding (GMAW) processes operated with aluminum and iron wire electrodes. It has been demonstrated, that this technique can be applied to transient GMAW processes in the presence of metal vapor. It has yielded spatially and temporally resolved electron density and temperature profiles without previous knowledge of plasma composition, the arc column shape and without the assumption of local thermal equilibrium (LTE). The measurement data could be additionally used for spatially and temporally resolved plasma composition estimation. Stark broadening is a passive spectroscopic technique, which relates the width of resonance lines emitted by the plasma to the free electron temperature and density. The emission spectra of stationary GTAW processes operated with pure argon and with argon-helium gas mixture as well as the pulsed GMAW processes operated with aluminum as the wire electrode have been investigated by means of this technique. It has been successfully applied for the spatially and temporally resolved electron density determination without assumption of LTE. Temperature values have been additionally estimated, when LTE assumptions were taken into account. The comparison of Thomson scattering and Stark broadening techniques has shown, that both methods deliver comparable results for electron density within the experimental error of the respective methods. Good agreement with the experimental results available in the literature could be also found for both techniques at least for the stationary processes, since not much data for transient processes exist.    «

Shielded gas arc welding is an indispensable technology for joining all kinds of metals. In order to guarantee, that those processes fulfill high requirements for modern industrial applications, they take advantage of e.g. specific gas compositions or transient current phenomena for production of reliable welding joints. However, for a stable and safe process operation a profound understanding of the physics taking place in the arc plasma is needed. The level of knowledge for basic welding proce...    »