Acoustic emissions in directed energy deposition processes

Abstract

Acoustic emissions in directed energy deposition processes such as wire arc additive manufacturing and directed energy deposition with laser beam/metal are investigated within this work, as many insights about the process can be gained from this. In both processes, experienced operators can hear whether a process is running stable or not. Therefore, different experiments for stable and unstable processes with common process anomalies were carried out, and the acoustic emissions as well as process camera images were captured. Thereby, it was found that stable processes show a consistent mean intensity in the acoustic emissions for both processes. For wire arc additive manufacturing, it was found that by the Mel spectrum, a specific spectrum adapted to human hearing, the occurrence of different process anomalies can be detected. The main acoustic source in wire arc additive manufacturing is the plasma expansion of the arc. The acoustic emissions and the occurring process anomalies are mainly correlating with the size of the arc because that is essentially the ionized volume leading to the air pressure which causes the acoustic emissions. For directed energy deposition with laser beam/metal, it was found that by the Mel spectrum, the occurrence of an unstable process can also be detected. The main acoustic emissions are created by the interaction between the powder and the laser beam because the powder particles create an air pressure through the expansion of the particles from the solid state to the liquid state when these particles are melted. These findings can be used to achieve an in situ quality assurance by an in-process analysis of the acoustic emissions.

Effects of Contaminations on Electric Arc Behavior and Occurrence of Defects in Wire Arc Additive Manufacturing of 316L-Si Stainless Steel

“…This occurs by observing the peak occurrences around 250 A, which corresponds to the established peak current for the process, and a lower plateau of occurrence numbers associated to 50 A that was established as the reference base current for the transfer mode. Specifically, the highest occurrences for the base and peak current values were obtained for sample S 3 , since it is understood that the inclusion of contaminants disperses the pre-configured values for these parameters and, consequently, reduces the level of occurrences for these, as similarly discussed in [48], when evaluating different experimental conditions on CMT-WAAM transfer and deposit geometrical characteristics. This observation implies a notable stability of the welding arc, contrasting with sections in other samples where the contaminants were introduced.…”

Advancements in 3D Printing: Directed Energy Deposition Techniques, Defect Analysis, and Quality Monitoring

“…AE signals, characterized as one-dimensional, time-dependent data, requires less computational effort to process and can reveal distinct variations associated with different levels of porosity and power [235,238], as shown in Figure 20. This reduces the need for subsequent quality assurance, making the entire process more efficient and economical [239]. The development of AE sensing technologies is, thus, critical for detecting defects in metal AM.…”

Anomaly Detection in WAAM Deposition of Nickel Alloys—Single-Material and Cross-Material Analysis

“…A variety of research works indicate the utility of acoustic signal analysis in anomaly detection during WAAM deposition [15][16][17]. Defects that are linked to arc instabilities, including porosity, spatter and lack-of-fusion, typically show distinct audio signatures.…”