Ultrasonic in situ measurements for hybrid metal additive manufacturing

Abstract

Hybrid additive manufacturing (AM) of metals includes synergistic secondary processes such as milling or peening that impart changes to the component for improved performance. Although a valuable concept, implementation is difficult to verify due to a current lack of in situ inspection methods. In this presentation, two different strategies are described with respect to ultrasonic inspections for hybrid metal AM. Both are used for inspections during laser-based directed energy deposition with milling as the hybrid process. The first uses a transducer mounted below the build plate. This configuration allows waves to interrogate the entire sample during all additive and subtractive manufacturing steps. Experiments with Ti6Al4V show the changes in ultrasonic wave speed and attenuation that track the manufacturing temporally. The second inspection approach uses ultrasonic surface waves at the top surface of the sample. These measurements are used on samples of 316L stainless steel at the end of additive steps as well as before and after milling to quantify localized information regarding the most recent layers. Wave speed and diffuse scattering information show the variability with respect to sample geometry, build height, and process parameters. Finally, advantages and limitations of both approaches and prospects for validated parts are discussed.