Shortly after its invention, the laser was identified as a tool for precision heat delivery in metal manufacturing (cutting and welding). However, recently the opportunities for process enhancement with laser-based heat delivery have grown dramatically with metal additive manufacturing (3D printing)and laser-based material treatment (annealing, shock peening). Furthermore, practical lasers at increasingly higher powers are enabling traditional laser welding and cutting to find application in wider parameter space. NIST is assisting these industrially relevant processes by developing in-situ monitoring techniques to better quantify the process. This includes spectroscopic techniques for identifying alloy element loss during laser-metal interactions as well as radiometric techniques for measuring dynamic light coupling and laser parameters. This work presents two broad opportunities for a postdoctoral researcher.
Spectroscopic work is currently being done at NIST to provide real-time identification and quantification of alloy element losses in the vapor plume during laser material processing. This is being done through laser induced fluorescence (LIF) which provides enhanced sensitivity and specificity [1,2]. Opportunities for a post-doctoral researcher to expand this work include implementing planar laser induced fluorescence (PLIF) to permit 3D imaging of alloy element distribution in the weld plume, or the development of a way to use a CW laser (rather than a Q-switched YAG) to permit development of a compact LIF instrument which could be deployed in a manufacturing environment for real-time process feedback.
The radiometric work is designed to measure the dynamic coupling of the laser light into the metal workpiece as it goes from solid to liquid and interacts with ejected vapor and particles . Our effort is in measuring the total light “budget”; measuring source, scattered, and reflected power using an integrating sphere and calibrated detection to determine the dynamic light absorption by the metal. This indicates the phase and geometry changes in the metal and has being paired with a variety of complimentary techniques. Our high accuracy measurement provide reliable data for software modelling of laser welding and additive manufacturing processes.
 B.J. Simonds, P. Williams, J. Lehman, “Time-resolved detection of vaporization during laser metal processing with laser-induced fluorescence,” Procedia CIRP, 74, 628-631, (2018).
 B.J. Simonds, J. Sowards, and Paul A. Williams, “Laser-induced fluorescence applied to laser welding of austenitic stainless steel for dilute alloying element detection,” J. Phys. D: Appl. Phys. 50, 325602, (2017).
 B.J. Simonds, J.W. Sowards, J. Hadler, E. Pfeif, B. Wilthan, J. Tanner, C. Harris, P.A. Williams, J. Lehman, “Dynamic and absolute measurements of laser coupling efficiency during laser spot welds,” Procedia CIRP, 74, 632-635 (2018).
Laser; Laser welding; Additive manufacturing; Laser induced fluorescence; Spectroscopy; Metrology; Modelling; Sintering; 3D printing;