Monitoring of Laser Powder Bed Fusion by Acoustic Emission: Investigation of Single Tracks and Layers

Abstract

Quality concerns in laser powder bed fusion (L-PBF) include porosity, residual stresses and deformations during processing. Single tracks are the fundamental building blocks in L-PBF and their shape and geometry influence subsequent porosity in 3D L-PBF parts. The morphology of single tracks depends primarily on process parameters. The purpose of this paper is to demonstrate an approach to acoustic emission (AE) online monitoring of the L-PBF process for indirect defect analysis. This is demonstrated through the monitoring of single tracks without powder, with powder and in layers. Gas-borne AE signals in the frequency range of 2–20 kHz were sampled using a microphone placed inside the build chamber of a L-PBF machine. The single track geometry and shape at different powder thickness values and laser powers were studied together with the corresponding acoustic signals. Analysis of the acoustic signals allowed for the identification of characteristic amplitudes and frequencies, with promising results that support its use as a complementary method for in-situ monitoring and real-time defect detection in L-PBF. This work proves the capability to directly detect the balling effect that strongly affects the formation of porosity in L-PBF parts by AE monitoring.

When am (additive manufacturing) meets ae (acoustic emission) and AI (artificial intelligence)

“…As mentioned in the introduction, AE system is one of the most effective monitoring methods for dynamical processes [15]. Due to its advantages, AE sensors have been used in AM, particularly L-PBF for online quality monitoring [16,[23][24][25][26][27][28][29] and combining AI [9,14,[17][18][19][20][21][22]30]. It is important to mention that these publications have in common the fact that experiments are conducted for single material and single process parameter per regimes and/or category.…”

“…Still, the data processing was straightforward and primarily qualitative. Finally, since 2020, the number of scientific contributions using AE for online monitoring of LPBF has increased significantly, each addressing a specific scientific question and bringing a small stone towards the development of a universal online monitoring system for laser AM processes [25][26][27][28][29][30].…”

Developing a Ti6Al4V specimen to induce residual stress deformations and cracks for use in metal additive manufacturing online monitoring

“…Deformations and cracks within the material caused by the residual stresses pose a quality assurance challenge for industries. Modern methods of attempting to address these challenges are in instances being implemented, and further investigated, such as the use of thermal based online monitoring techniques [7], acoustic emitted signal monitoring techniques [8], and build-plate sensors used by Hehr et.al. [9] which were used to detect the deformation and delamination of the parts during the L-PBF build process by means of a fibre optic sensor which measured the strains in the buildplate as the deformation occurred.…”

Assessment of the Integrity of Reinforced Concrete Beams Strengthened With Carbon Fibre Reinforced Polymer Using the Acoustic Emission Technique

“…The acoustic emission technique, one of the NDT techniques, is relatively easy to install and capable of predicting the location in which damage has occurred. Acoustic emission is a versatile method as it can be developed and applied with different approaches and for specific needs (Kouprianoff et al, 2021). Not only is it versatile, but the acoustic emission technique also analyses the properties of elastic waves caused by microscopic damage in a concrete member (Yun et al, 2010).…”