Detecting Selective Laser Melting Beam Power from Ultrasonic Temporal and Spectral Responses of Phononic Crystal Artifacts Toward Real-Time Quality Monitoring.

Unlike many conventional manufacturing techniques, 3D Printing/Additive Manufacturing (3DP/AM) fabrication creates builds with unprecedented degrees of structural and geometrical complexities. However, uncertainties in 3DP/AM processes and material attributes could cause geometric and structural quality issues in resulting builds and products. Evaluating the sensitivity of process parameters and material properties for process optimization, quality assessment, and closed-loop control is crucial in practice. This study presents a framework for a nondestructive real-time ultrasonic monitoring approach based on the temporal and spectral dispersion analyses of specially designed artifacts with periodic internal structures called Phononic Crystal Artifacts (PCAs). The framework's effectiveness for monitoring of laser beam power in a Selective Laser Melting (SLM) process is experimentally demonstrated. A PCA is significantly simpler and/or smaller than the actual build, but it represents a specific subset of its geometric and mechanical features and complexities, which are relevant to the objectives of a quality monitoring program. Specifically, the influence of the SLM printer laser beam power on the ultrasonic responses and dispersion properties of stainless steel 316L PCAs is evaluated. Two sensing strategies based on cross-correlation and spectral dispersion analysis of ultrasonic waves transmitted in the artifacts are presented and utilized for evaluating the effect of laser power level on the mechanical and microgeometric properties of fabricated PCAs. The reported novel framework's potential in critical quality monitoring applications for real-time quality assessment of 3DP/AM processes is also discussed.