Acoustic Source Localisation of Crack Initiation During Laser-Based DED: Experimental Validation and Challenges

Area of Science:

• Materials Science and Engineering
• Additive Manufacturing
• Non-Destructive Testing

Background:

• Cracks are critical defects in laser-based directed energy deposition (DED-LB/M) additive manufacturing.
• In situ monitoring is crucial for real-time defect detection and process control.

Purpose of the Study:

• To evaluate the feasibility of airborne acoustic source localisation (ASL) for in situ crack localisation in DED-LB/M.
• To assess the accuracy and limitations of ASL for identifying crack positions during fabrication.

Main Methods:

• Utilised a four-microphone array and Generalised Cross-Correlation with Phase Transform (GCC-PHAT) algorithm.
• Optimised microphone array geometry numerically for industrial constraints.
• Estimated crack positions from acoustic emissions and time differences of arrival (TDOAs).
• Validated results against post-process microscopic measurements.

Main Results:

• Localisation errors varied: X (12-68 mm), Y (0.7-32 mm), Z (5-100 mm).
• Achieved centimetre-scale accuracy for horizontal crack localisation.
• Depth (Z-direction) estimation showed greater variability.
• Confirmed ASL provides spatial information on crack formation.

Conclusions:

• Airborne ASL is industrially feasible for in situ crack investigation in DED-LB/M.
• Performance is sensitive to TDOA accuracy, array constraints, and acoustic environment.
• Further advancements in array design and signal processing are needed for robust 3D defect localisation.