Quantitative Optical Measurements of Laser-Matter Interaction in Metal Additive Manufacturing
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The testbed for research on Fundamentals of Laser-Matter Interaction (FLaMI) in laser-based metal additive manufacturing (AM-LB/M) was developed at the National Institute of Standards and Technology (NIST) for the primary purpose of implementing unique and high-fidelity optical metrology under highly controlled conditions. The testbed allows for more accurate machine characterization and more precisely controlled processing parameters than a typical 3D build machine, while still representing laser processing conditions in AM. Machine performance calibrations included that of laser power, power density distribution, scan speed, turnaround time, positioning accuracy, and more, which will be briefly discussed. The goal of this research platform is to optically measure the fundamental characteristics of laser-matter interaction in physically accurate and meaningful units. Two unique measurements at the laser wavelength include that of the total reflected laser power (up to ≥ 1 MHz temporal resolution) and the directionally resolved reflected laser light distributions (at 60 kHz). Furthermore, high-speed imaging, up to 150 kHz with magnification of 1.8 μm/pixel, was used to visualize the melt pool and particle dynamics with accurate reference to the processing laser position. Particle and spatter dynamics are additionally measured with shadowgraphy with imaging speeds of 67.5 kHz with resolution of 14.5 μm/pixel. Finally, spectroscopy was used to identify emission bands from the byproducts plume of Ti-6Al-4V to then measure the spatial and spectral properties under varied processing parameters.