Online laser-induced breakdown spectroscopy for metal-particle powder flow analysis during additive manufacturing

The analysis of the metal powder flow during an additive manufacturing process was carried out by laser-induced breakdown spectroscopy (LIBS). Coaxial laser cladding is an additive manufacturing technology (laser direct metal deposition) based on a part build-up process with metal powder melting by a powerful continuous wave laser. A compact and lightweight LIBS probe was designed to equip the laser cladding setup. Metal powder jet ablation by the LIBS probe was carried out to protect the probe's optics and to use a non-gated spectrometer. Poor LIBS measurement reproducibility was observed for metal powder jet ablation compared to that for a solid metal target. Two different procedures for calibration curve construction ("spectra counting" and "spectra averaging") were compared in terms of root mean square error of cross-validation (RMSECV) and curve linearity (R-2). Better analytical capabilities of online LIBS analysis for tungsten and nickel were achieved with the "spectra averaging" approach.