Optical emission spectroscopy of tungsten inert gas wire-arc plasma for in situ monitoring in additive manufacturing

In situ diagnostics for defect detection and compositional assessment remain critical for addressing persistent challenges in Additive Manufacturing (AM). Among the available diagnostic techniques, Optical Emission Spectroscopy (OES) stands out for its strong capability to provide in situ and non-intrusive monitoring of the AM process. As part of our ongoing efforts to develop a low-cost, real-time AM monitoring tool, this study represents an initial investigation focused on the concentration of key species in the Tungsten Inert Gas (TIG) wire-arc plasma generated during welding of an aluminum (Al-6061-T6) sheet using OES. Emission spectra from the arc plasma were analysed to identify and quantify key spectral lines associated with aluminum and potential alloying elements. The plasma temperature and electron number density were estimated to support quantitative analysis through Boltzmann and Saha methods to enable accurate concentration determination by calibration-free approach. The results demonstrated the potential of OES as an effective tool for monitoring and optimizing the aluminum welding operations through in situ non-intrusive plasma composition analysis.