Laser ultrasonic testing for near-surface defects inspection of 316L stainless steel fabricated by laser powder bed fusion

Abstract

The laser powder bed fusion (L-PBF) method of additive manufacturing (AM) is increasingly used in various industrial manufacturing fields due to its high material utilization and design freedom of parts. However, the parts produced by L-PBF usually contain such defects as crack and porosity because of the technological characteristics of L-PBF, which affect the quality of the product. Laser ultrasonic testing (LUT) is a potential technology for on-line testing of the L-PBF process. It is a non-contact and non-destructive approach based on signals from abundant waveforms with a wide frequency-band. In this study, a method of LUT for on-line inspection of L-PBF process was proposed, and a system of LUT was established approaching the actual environment of on-line detection to evaluate the method applicability for defects detection of L-PBF parts. The detection results of near-surface defects in L-PBF 316L stainless steel parts show that the cracktype defects with a sub-millimeter level within 0.5 mm depth can be identified, and accordingly, the positions and dimensions information can be acquired. The results were verified by X-ray computed tomography, which indicates that the present method exhibits great potential for on-line inspection of AM processes.

Prediction of Manufacturing Parameters of Additively Manufactured 316l Steel Samples Using Ultrasound Fingerprinting

“…Using ultrasound, high frequency sound waves are transmitted into a material and the reflections from internal interfaces are used to evaluate the material's properties. It is used to detect surface and subsurface defects (NDT), measure thickness, and determine the properties of materials such as metals (NDE) [9]. Ultrasound based NDE techniques allow for the detection of defects or flaws that may not be visible to the naked eye.…”

Laser-based ultrasound interrogation of surface and sub-surface features in advanced manufacturing materials

“…Here we propose an all-optical ultrasound system suitable for in situ characterization of single LPBF melt lines. Laser based ultrasound (LBU) has previously been studied for use on AM samples including for detecting residual stresses 24 , subsurface defects using bulk waves 25 , surface defects using resolved acoustic spectroscopy 26 , and subsurface features using Rayleigh and Lamb waves 27 . Rayleigh (surface acoustic) waves are promising for characterizing laser melt lines because they are sensitive to surface and near surface features.…”

Eddy Current Testing of Artificial Defects in 316L Stainless Steel Samples Made by Additive Manufacturing Technology

“…Ultrasonic testing was the essence of sensor development by Slotwinski, J A, et al [ 21 ], intended for porosity monitoring in metal AM products. Additionally, laser ultrasonic testing was applied for an in situ evaluation of subsurface defects in AISI 316L stainless steel [ 22 ] and for residual stress identification in a titanium alloy (Ti-6Al-4V) [ 23 ]. For the detection of microdefects in AM material, an acoustic emission was used by Ito, K, et al [ 24 ].…”