Measurement of melt pool dynamics in stationary laser welding using inline coherent imaging (Conference Presentation)

Troy R. Allen; Faleh AlTal; Brian J. Simonds; James M. Fraser

doi:10.1117/12.2509003

8 March 2019 Measurement of melt pool dynamics in stationary laser welding using inline coherent imaging (Conference Presentation)

Troy R. Allen, Faleh AlTal, Brian J. Simonds, James M. Fraser

Author Affiliations +

Proceedings Volume 10911, High-Power Laser Materials Processing: Applications, Diagnostics, and Systems VIII; 109110H (2019) https://doi.org/10.1117/12.2509003
Event: SPIE LASE, 2019, San Francisco, California, United States

Abstract

In laser welding and additive manufacturing, melt pool behavior is directly related to final part quality as instability can lead to pore formation and ejected spatter. In transition and keyhole mode welding of metals, the dynamic balance of forces working to open and close the resulting vapor cavity gives rise to melt pool surface oscillations at frequencies on the order of kHz. Existing process monitoring techniques, such as high-speed video, have been extremely useful to image melt pool boundaries, but are limited in their ability to quantifiably track oscillation amplitudes and monitor high-aspect ratio features. We exploit inline coherent imaging (a through-the-lens technique based on low coherence interferometry) to directly measure melt oscillations through the transition zone (from conduction to keyhole welding). An Yb:fiber laser is used to perform 10ms spot welds on 316 stainless steel with varying laser powers (120-630W). Morphology is measured in situ at a rate of 170kHz. Oscillations are observed starting at the onset of the transition zone (irradiance 0.63MW/cm²) with a frequency of 10.0 ± 0.3kHz. At higher power (keyhole mode, irradiance 1.8MW/cm²), the bottom of the keyhole oscillates with a frequency of 2.5 ± 0.5kHz around a maximum depth of 1mm. This trend agrees with analytic modelling dependent on melt surface tension, density and diameter, as well as complementary experiments that track total laser absorptance using an integrating sphere.

Conference Presentation

Citation Download Citation

Troy R. Allen, Faleh AlTal, Brian J. Simonds, and James M. Fraser "Measurement of melt pool dynamics in stationary laser welding using inline coherent imaging (Conference Presentation)", Proc. SPIE 10911, High-Power Laser Materials Processing: Applications, Diagnostics, and Systems VIII, 109110H (8 March 2019); https://doi.org/10.1117/12.2509003

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KEYWORDS

Coherence imaging

Laser welding

Image processing

Additive manufacturing

Coherence (optics)

Interferometry

Metals

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