Laser Ultrasound Detects Metal 3D Printing Defects

Researchers have developed a new laser ultrasound technique capable of performing on-demand characterization of melt tracks and detecting the formation of defects in a popular metal 3D printing process.

The researchers propose a diagnostic using surface acoustic waves (SAW), generated by laser ultrasound, that can reveal tiny surface and sub-surface defects in laser powder bed fusion (LPBF) metal 3D printing. The system can effectively and accurately evaluate laser melt lines — the tracks where the laser liquefies metal powder in LPBF printing — by scattering acoustic energy from melt lines, voids, and surface features that can be quickly detected. The team validated the findings using optical microscopy and X-ray computed tomography (CT).

The research demonstrates the potential for an all-optical ultrasound system capable of rapid, on-demand in situ characterization of LPBF processes and powders. The demonstrated laser-based ultrasound surface acoustic wave system showed excellent sensitivity to surface and near-surface features, including breaks in the LPBF melt line, metal surface splatter, and subsurface air voids.

Surface acoustic waves have historically been used in engineering materials to characterize surface, and near-surface features such as cracks, pits, and welds and are now used in geology — on a much larger length scale — to detect underground features such as caves. According to the researchers, SAWs are well-suited for characterizing melt lines in LPBF printing due to their surface and near-surface sensitivity.

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