Image denoising for laser ultrasonic inspection of wire arc additive-manufactured components with a rough surface

ABSTRACTLaser ultrasonic testing (LUT) is a non-contact and non-destructive testing (NDT) technique which can detect the wire arc additive manufacturing (WAAM) component defect in hot state. However, the complex surface topography of the WAAM component induces a low signal to noise ratio (SNR) and a poor detection sensitivity. In this paper, a denoising method based on improved empirical mode decomposition with adaptive noise (ICEEMDAN) and Wavelet Packet Transform (WPT) was applied in the LUT of the WAAM component. All the signals in the LUT scan maps with low SNR were decomposed into a series of intrinsic mode functions (IMFs) using ICEEMDAN. The Pearson correlation coefficient of the original signal and the IMFs were calculated. The high frequency (HF) and low frequency (LF) IMFs with correlation coefficients under the threshold were denoised using WPT and deleted, respectively. The denoised IMFs and the IMFs without processing were stacked up to compose the denoised signal and plot the denoised scan maps. The denoising results show that the proposed method improved the LUT efficiency and sensitivity. Finally, the denoising method was applied and verified in the LUT of the WAAM nuclear power pipeline nozzle.KEYWORDS: laser ultrasonicWAAMICEEMDANWPTscan mapnuclear power pipeline Abbreviation AM=Additive manufacturingWAAM=Wire arc additive manufacturingDED=Directed energy depositionPBF=Powder bed fusionSLM=Selective laser meltingLPD=Laser powder depositionEBD=Electron beam depositionCMT=Cold metal transfer3D=Three-dimensionalWHR=Width-height ratioSDH=Side-drilled holeLUT=Laser ultrasonic testingNDT=Nondestructive testingSNR=Signal to noise ratioEMD=Empirical mode decompositionEEMD=Ensemble empirical mode decompositionCEEMD=Complementary ensemble empirical mode decompositionCEEMDAN=Complete ensemble empirical mode decomposition with adaptive noiseICEEMDAN=Improved empirical mode decomposition with adaptive noiseWT=Wavelet TransformWPT=Wavelet Packet TransformIMF=Intrinsic mode functionTOF=Time of flightHF=High frequencyLF=Low frequencyLUSS=Laser ultrasonic scanning systemAcknowledgmentsThe authors would like to thank the National Key R&D Program of China (No.2019YFB1704500), the National Natural Science Foundation of China (No.51875428), the Key R&D Program of Hubei province (No.2020BAB144) and Excellent Youth Foundation of Hubei province (No.2019CFA041), and the 111 Project of China (No. B17034).Disclosure statementNo potential conflict of interest was reported by the author(s).