Real-time characterization of laser-generated melt pools using ultrasound

In this article, ultrasound is used to monitor the real-time evolution of laser-generated melt pools created on the surface of a stainless steel plate. A plurality of spherically focused immersion transducers was used to measure various shear scattering amplitudes from the generated melt pool as it evolves with increasing laser duration. The scattering of ultrasound out of the plane of incidence is found to be particularly sensitive to melt pool depth. A finite element model that incorporates both conductive thermal transport and elastodynamic wave propagation is used to help confirm the existence of scattering from the melt pool and the temperature field around it. Lastly, the scattered response is found to exhibit a temporal evolution that follows the temperature evolution in the plate. This work represents a step forward in the development of a real-time ultrasonic technique to (1) qualify additively manufactured parts, and (2) characterize melt pools created during additive manufacturing processes. keywords: additive manufacturing, ultrasonic scattering, real-time methods, welding.