Irregularities in process conditions during powder bed fusion (PBF) additive manufacturing (AM) can lead to localized defects and poor part quality. At the same time, because PBF-AM is a layer-by-layer process, material properties such as defect concentration can be characterized in situ, thus providing an opportunity to ‘qualify as you build.’ Here we review methods based on high speed, multi-wavelength optical measurements of melt pool evolution, material ejection and layer-to-layer height variation during PBF processing, and compare the results to ex situ x-ray tomographic measurements. We also discuss the complex mechanisms related to the interaction between the melt pool, laser beam, and powder bed which ultimately drive defect formation. Along with providing process monitoring data to facilitate part certification, data provided by in situ optical diagnostics can help validate process models. The practical implementation of these high speed diagnostics into commercial platforms is also discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Manyalibo J. Matthews, "Additive manufacturing of metals as seen from within: in situ optical probes for defect mapping (Conference Presentation)," Proc. SPIE 10597, Nano-, Bio-, Info-Tech Sensors, and 3D Systems II, 1059708 (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 05, 2018; Published: 27 March 2018); https://doi.org/10.1117/12.2299494.5759118828001.
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