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Proceedings Paper

In-process imaging of morphology and temperature for laser welding and selective laser melting (Conference Presentation)

Paper Abstract

Directly measuring morphology and temperature changes during laser processing (such as in keyhole welding and selective laser melting) can help us to understand, optimize, and control on-the-fly the manufacturing process. Even with such great potential, the technical requirements for such an in situ metrology are high due to the fast nature of the highly localized dynamics, all the while in the presence of bright backscatter and blackbody radiation, and possible obstructions such as molten ejecta and plumes. We have demonstrated that by exploiting coherent imaging through a single-mode fiber inline with the processing lens, we can image morphology at line rates up to 312 kHz, with sufficient robustness to achieve closed loop control of the manufacturing process. Applied to metal additive manufacturing, inline coherent imaging can directly measure powder layer thickness and uniformity, and formed track roughness including the onset of balling. Inline coherent imaging measures morphology dynamics but that is only part of the story. Temperature is also key to final part quality. Standard thermal imaging exploits blackbody radiation but are plagued by the highly variable emissivity of the region of interest, making quantitative measurement challenging. We were able to exploit the same apparatus used for coherent imaging to collect surface temperature profiles. Since we spectrally resolve a wide signature, we have overcome the emissivity problem to measure absolute temperature on the micron scale during laser processing.

Paper Details

Date Published: 13 May 2019
Proc. SPIE 10991, Dimensional Optical Metrology and Inspection for Practical Applications VIII, 109910V (13 May 2019); doi: 10.1117/12.2520188
Show Author Affiliations
Tristan G. Fleming, Queen's Univ. (Canada)
Troy R. Allen, Queen's Univ. (Canada)
Stephen G. L. Nestor, Queen's Univ. (Canada)
Faleh AlTal, Queen's Univ. (Canada)
James M. Fraser, Queen's Univ. (Canada)

Published in SPIE Proceedings Vol. 10991:
Dimensional Optical Metrology and Inspection for Practical Applications VIII
Kevin G. Harding; Song Zhang, Editor(s)

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