In-process optical monitoring has led to impressive enhancements in the quality control of metallic parts made by wire and arc additive manufacturing (WAAM). Identification of material defects during a WAAM process gives an opportunity to reduce post-process inspection, to pause the deposition to address the defect problem or terminate the process to save resources. This is of importance in the aerospace sector, where inferior quality components can have significant cost penalties. Many process factors, including deposition parameters, WAAM equipment, feedstock, the surrounding atmosphere and contaminants can all contribute to create a defect in the component. The contaminants can be introduced as organics (oils / grease) or inorganic elements coming from the deposition atmosphere, the WAAM system itself or the feedstock material. Contamination by tungsten (originating in the plasma torch electrode) is a particular concern as its melting point, 3422C, is much higher than that of titanium alloy (1674C for Ti-6Al-4V)[1]. Within the WAAM melt pool, a solidified drop of tungsten can remain dissolved which could result in a defect in the final part under tensile loading. Here, we demonstrate the development of an optical emission spectroscopy system to identify tungsten as a contaminant. Spectra were obtained from the plasma during the process using a spectrometer with an integration time of 110ms. Data analysis was undertaken to average over longer timescales, and unambiguously identify the emission lines of contaminating tungsten.
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