In-Situ Monitoring of Laser Additive Manufacturing for Al7075 Alloy Using Emission Spectroscopy and Plume Imaging

Most aluminum alloys, especially the 7xxx series, are incompatible with laser additive manufacturing due to many factors. In-situ process monitoring technology offers an excellent opportunity for process understanding and control, which improves the component quality and repeatability of AM. In this study, emission spectroscopy and plume imaging were utilized to monitor and understand the laser-directed energy deposition of Al7075 alloy. Characteristics of plasma were analyzed using spectra and plume image signals. Emission lines of Al I, Mg I, and Cr I observed in spectra signals demonstrated that primary elements in Al7075 were evaporated and excited during the AM process forming a plasma plume. The plasma plume intensity increased significantly as the laser power increasing. The periodic fluctuation of plasma was revealed using plume images, indicating that laser powers inputted into the target surface were unstable due to the laser and plasma interaction. The elemental evaporation and inconsistent laser input are the main challenges for Al7075 AM and are potentially monitored by plasma signals. Methods of signal process and feature extraction for spectra and plume images were developed. Experimental results showed that the aluminum emission spectral energy, the average baseline spectral intensity, and the plume area are practical for rough surface monitoring. Correlations between spectral features and key printing parameters were developed, demonstrating an excellent response of spectra features to the laser power and laser scanning speed. This investigation revealed the potentials and challenges of emission spectroscopy in the in-situ monitoring of laser AM, making progress towards intelligent additive manufacturing.