4th Symposium on Materials and Additive Manufacturing
Lecture
14.06.2024 (CEST)
In situ Crack detection during Laser Directed Energy Deposition using frequency resolved Acoustic Emission Testing
JM

Dipl.-Ing. Jacob-Florian Mätje

Fraunhofer-Institut für Werkstoff- und Strahltechnik IWS

Mätje, J.-F. (Speaker)¹; Hendel, J.²; Riede, M.¹; Lopez, E.¹; Brückner, F.¹; Leyens, C.²
¹Fraunhofer Institute for Material and Beam Technology IWS, Dresden; ²TUD Dresden University of Technology
Vorschau
19 Min. Untertitel (CC)
One of the main barriers to utilizing additive manufacturing (AM) in an industrial environment is reliable quality control. To ensure the repeatability and cost-effectiveness of AM parts, in situ non-destructive testing (NDT) is a very useful tool. Prevalent in situ NDT tools, are mainly based on optical or infrared imaging; hence, the data gained is mainly related to surface information. However, for the quality of mechanically stressed parts, avoiding internal defects is of great importance due to their great impact on the (fatigue) strength. Promising results for in situ NDT can be obtained by using Acoustic Emission Testing (AET), a method that analyses acoustic emissions which occur from solids when a material undergoes changes in its internal structure. Defects are discerned from variations in the intensity of acoustic emissions during defect formation in contrast to the base acoustic signal. AET is already being used for detecting and tracking defects in structures like wind turbines. Concluding, this method has great potential for AM regarding in situ quality control. However, due to the inherently passive signal detection, adapting the approach for Directed Energy Deposition presents significant challenges that need to be addressed. These include signal interference from the process environment, variations in acoustic behaviour between different setups, and the constantly changing geometry due to material buildup.


This work aims to demonstrate that by obtaining a time- and frequency-resolved intensity distribution, these challenges can be overcome and distinguished acoustic patterns of defects and random interference can be analysed. To gain an understanding of the acoustic emission profiles that occur during deposition and to set up thresholds for automated defect detection, two types of samples are fabricated and monitored using enhanced AET: near defect-free references and samples that crack during processing. The recorded intensity distributions are analysed to identify possible cracks. Samples are further investigated using µ-focus computer tomography to confirm the presence of defects and ensure the quality of the reference. A correlation between defect size, acoustic profile, and crack location can be made to evaluate the suitability of in situ AET for quality control.

Abstract

Abstract

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