Quantitative Imaging Detection of Additive Manufactured Parts Using Laser Ultrasonic Testing

Selective laser melting (SLM) is an important method of additive manufacturing, however it has some disadvantages such as poor surface qualities of the formed parts and the appearances of small surface defects. In this article, 360L stainless steel with artificial defects in different lengths are processed by SLM processing. A full noncontact laser ultrasonic-based B-scan detection system is built to detect the surface defects. The interaction between the scattered surface wave and the surface defect is verified through 3-dimension (3D) finite element simulation. In order to improve the signal-to-noise ratio (SNR) of laser ultrasonic signal in AM 316L part, Variational Mode Decomposition (VMD) algorithm based particle swarm optimization (PSO) is applied to denoise signals. Meanwhile, wavelet transform (WT) algorithm is used to compare SNR with VMD algorithm. Then, the time and amplitude parameters of different positions are extracted to realize B-scan imaging, and the lengths of defects are further accurately quantified through the time-amplitude-position imaging images. Otherwise, we find that the size of laser spot affects the precise quantification of defects. The smaller the spot is, the more precise the quantitative effect is. The results show that this method can quantitatively detect surface defects of AM 316L parts.