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Etude des mécanismes de génération des stries dans le procédé de découpe laser d'aciers

Abstract : This study investigates the mechanism of striation generation in inert gas laser cutting of steel. In spite of its scientific and industrial importance, the mechanism has remained unknown for several decades. First, hydrodynamics of molten liquid on a kerf front is experimentally observed using a high speed video camera. Observation from the above of a sample reveals for the first time generation of melt flow instabilities from the sample surface. Unstable melt flow involves molten droplets: so called humps and melt accumulations, in the central and side parts of the kerf front, respectively. It is clearly observed that striations are generated by periodic generation and downward displacement of the melt accumulations along kerf sides. Lateral observation of a kerf front through a glass plate demonstrates that also humps in the central part can disturb the dynamics of the melt accumulations and degrade quality of striations. Then the origin of the observed instabilities is discussed. Characteristics of the melt flow instabilities observed both in the central and side parts can be explained coherently by a unique mechanism related to surface tension. We consider that striations are created by local melting of solid surface due to heat transfer from the melt accumulations. Surface roughness is theoretically predicted by a heat transfer analysis and the result roughly agrees with experimental results. Finally, using the newly revealed mechanism of striation generation, we discuss an interesting topic of cut surface quality difference between 1 and 10 microns laser wavelengths. We propose two factors which can cause the wavelength dependence: stability of melt flow in the central part and absorptivity of laser beam on melt accumulations along the kerf sides. The validity of each mechanism is confirmed by analytical modelling of related physical processes.
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https://pastel.archives-ouvertes.fr/pastel-00751668
Contributor : Koji Hirano <>
Submitted on : Wednesday, November 14, 2012 - 7:10:09 AM
Last modification on : Friday, July 17, 2020 - 2:54:12 PM
Long-term archiving on: : Saturday, December 17, 2016 - 10:37:11 AM

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  • HAL Id : pastel-00751668, version 1

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Koji Hirano. Etude des mécanismes de génération des stries dans le procédé de découpe laser d'aciers. Mécanique [physics.med-ph]. Arts et Métiers ParisTech, 2012. Français. ⟨pastel-00751668⟩

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