Abstract: Mechanical properties of materials fabricated with additive manufacturing process are determined through optical monitoring in real time. A plasma generated in a zone where a laser interacts with deposited material is monitored using optical emission spectroscopy to generate one or more plasma spectral lines. The emission lines are analyzed to determine the hardness, micro-hardness, yield/residual stress, tensile strength, or other mechanical characteristics of the material. The composition may be an alloy such as an aluminum-magnesium alloy, including 7000 series aluminum alloys. The mechanical property may be derived from a change in a ratio of the plasma spectral lines, including a change in a ratio of ionic and neutral magnesium (Mg) associated with a 7000 series aluminum alloy. The apparatus and methods are extendable to other alloys and compositions.

Abstract: A smart additive manufacturing system uses a spectrometer to collect emission spectra along an optical axis from a laser-generated plasma plume, and wherein the laser beam and the optical axis of the emission spectra are co-axial, at least in the vicinity of the melt pool, thereby minimizing the fluctuation of spectral signals caused by ambient pressure/gas variations. The laser beam passes through a beam splitter prior to reaching the work piece, and the emission spectra from the work piece are redirected by the beam splitter to the spectrometer, and wherein the laser beam and the optical axis of the emission spectra are co-axial between the work piece and the beam splitter. The beam splitter may be a dichroic mirror or other type of beam splitter, including holographic beam splitters, and spectral filtering may be carried out with separate optical elements, as long as the overall goal of on-axis excitation and collection is achieved.