Advanced manufacturing techniques have advantages over traditional approaches in their ability to create complex geometries, internal features, and light-weight components. Laser powder bed fusion is a common advanced manufacturing technique in which a part is built in consecutive layers by laser melting of powder which is mechanically distributed over the surface. Intra- and inter-layer integrity is dependent upon rapid heating, melting, and solidification processes. Currently, there is a need for new techniques to provide *in situ* feedback on these processes. In this work, we describe a laser-based ultrasonic technique to probe thermal effects induced by a high-power continuous wave laser in titanium samples. A pulsed laser is used to generate high frequency surface acoustic waves that propagate through the laser-heated region and are subsequently detected using a photorefractive crystal-based interferometer. Wave propagation through the heated region is influenced by the temperature-dependent thermal properties of the sample and, at sufficiently high heating laser power, interaction with a liquid metal pool. We present experimental results showing the acoustic wave response as a function of heating laser power and melt pool size. Surface acoustic wave interaction with the laser heated region is also investigated using time domain finite element simulations. We consider both the low heating power regime where wave propagation is only influenced by the temperature-dependent thermal properties, and a higher power regime where the waves also interact with a melt pool. Our experimental and simulation results indicate that this laser ultrasonic technique may offer a means of tracking the subsurface temperature distribution and the spatial extent of the melt pool. Furthermore, this approach may ultimately find application in the real-time monitoring of laser powder bed fusion thermal processes.

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and was supported by the LLNL-LDRD Program under Project No. 19-ERD-008.

 


Laser Ultrasonic Monitoring of Thermal Processes

No proceedings papers in 2020. Video only.

QNDE2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.