Numerical and experimental study of attenuation inspection during FDM with ultrasonic leaky waveguide

This work proposes an ultrasonic leaky waveguide (ULWG) for in-situ structural integrity inspection during fused deposition modeling (FDM). Since the ultrasonic wave propagation speed (m·s−1) is much higher than the deposition speed (mm·s−1), a quasi-static finite element model is first established to simulate the wave propagation during this dynamic process. The amplitude and energy attenuation coefficients (α and ζ) are chosen as the inspection features. Processing parameters including deposition layer thickness and number, inspection frequency, plate thickness and interface impedance are explored. For the first layer printing, a thinner thickness, higher frequency and proper interface impedance will enable a better inspection with high sensitivity. For multilayer printing, the multimodal dispersion curves change continuously and α oscillation is observed due to waveform aliasing that ζ is more reliable. Printing failures such as detachment can be predicted as well from the model established. The ULWG is then integrated into a commercial FDM machine to capture the attenuation coefficients of an “S” shape sample. The poor adhesion, local and global detachments, path planning impact can all be revealed by ζ experimentally. Moreover, being consistent to the simulation, the fluctuation of α in multilayer printing increases, which prevents a further printing evaluation.