Tracking the evolution of structural resonances during the build phase of a wire-arc additively manufactured part

Acoustic resonance tracking is investigated for a wire arc additive manufacturing process as a possible real time in situ diagnostic during the build. A small 40kHz acoustic emission sensor was attached to one end of a 5 × 1.5 in. cylindrical 316 SS rod. A series of layers (weld beads) were programmed into the control software of the robot to build a thin bar upward off the end of the cylinder. A high-speed long-duration digitizer-recorder was used to capture the transient acoustic signals (100 Hz–70 kHz) during the build process. Typical build durations were on the order of 1–2 h. The transient data were analyzed using short time window FFTs, as a function of build parameters. The model and experiment share similar features, however there are some notable differences. In particular, the number of actual modes recorded in the experiment is less than predicted due to the sensors low in-plane sensitivity. The current results indicate that the evolving spectral response of a part during the build process has the potential to provide real time process monitoring information. The time-frequency analysis of the diffuse sound field in the part, reveals a unique spatial and temporal perspective of temperature, stress and geometric features.