THE LASER USER
ISSUE 114 AUTUMN 2024 LASER CUTTING
validates the observed increase in the number of smaller, high velocity particles present during air cutting. Preventing melt from being ejected effectively, leading to large dross formation, appears to reduce the occurrence of fine particle emissions.
Conclusions
The study's findings suggest that low-pressure laser cutting can be used as a technique to reduce the by-product emissions. However, this is at the detriment of cut quality. From the results presented here, reducing the shear stresses applied on the melt as well as melt temperature led to breakdown mechanisms that are more favourable for improved by- product generation. Hence, reducing assist gas pressure is recommended in applications such as nuclear decommissioning, where by-product formation and safety are of primary concern. For most optimal conditions it is recommend that nitrogen instead of air is used. Further research is recommended to refine these techniques and explore their applicability across various hazardous environments, as well as expand the understandings developed here to a wider range of industries.
Figure 2 (a-d) High speed images of melt ejection during laser cutting cut with different gases at different gas assist pressures. (a) 6 Bar air, (b) 3 Bar air, (c) 6 Bar nitrogen, (d) 3 Bar nitrogen. (e) Underside of plate after cut with air at different supply pressures. Cut 1 at 3 Bar, cut 2 at 4 Bar, cut 3 at 5 Bar.
Acknowledgements
This work has been funded by the UK Nuclear Decommissioning Authority (NDA) project “Bad Laser Cutting to Get Good Laser Fume” with supervision provided by the National Nuclear Laboratory (NNL).
References
[1] P. Hilton and A. Khan, “New developments in laser cutting for nuclear decommissioning,” WM Symposia Inc. 2014.
[2] A. Mallion et al, “LaserSnake2: Remote high powered laser cutting in confined hazardous spaces,” WM Symposia Inc. 2016.
[3] Lavin et al, “Controlling nozzle and kerf gas dynamics to manage hazardous laser cutting fume”, Journal of Laser Applications, 2022
[4] Lavin et al, “Reducing environmental risks in laser cutting: A study of low-pressure gas dynamics”, journal of Laser Applications, 2023
* L.C.R. Jones, E.J. Long, J.R. Tyrer, J.J. Robus T. Williams, M.T. Jones. Loughborough University. J.T. Spencer, J.M. Dodds. NNL (UK)
Figure 3: Change in shear stress along the cut depth for turbulent gas jet boundary layer.
the same pressure is not believed to be sufficient to justify the observed changes in breakdown mechanisms. However, the change in melt viscosity due to the change in melt temperature is significant. Based on the calculated melt temperatures, melt viscosities of 2.14 mPa.s for nitrogen and 1.65 mPa.s for air have been estimated. This reduction in melt viscosity
Contact: Jacob Lavin
J.Lavin@
lboro.ac.uk https://www.lboro.ac.uk/schools/ meme/
Jacob Lavin is a Research Associate at Loughborough University specialising in laser processing, thermofluids and optical diagnostics.
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