Laser ultrasonic technique to non-Destructively detect cracks on a Ni-Based self-Fluxing alloy fabricated using directed energy deposition (DED)

Abstract

Miniaturization of bearing rollers used in autos and robots will require a manufacturing system that combines a deposition method that can fabricate thin jigs without defects and a non-destructive inspection method that can detect cracks on such jigs. Here, we are developing a system that uses directed energy deposition (DED), which is a 3D-printing (additive manufacturing, AM) process, to fabricate thin jigs, and then uses laser ultrasonics (LU) to inspect the jigs. Here, deposited layers having a 0.4 © 0.6 mm2 cross-section were fabricated using DED, and then non-destructively inspected using LU. However, using LU on such a small area has three problems: the effect of overlapping of the excitation and detection laser beams, difficulty in separating the multiple types of waves due to the simultaneous generation, and complexity of the acoustic field. Therefore, first, the acoustic field was examined using the finite element method (FEM), and then LU was used to inspect a small area of the deposited layer using complex discrete wavelet transform. Results show successfully detection of spontaneously occurring cracks, thus confirming the effectiveness of LU for non-destructive inspection of a thin jig.