Contribution au développement d'un procédé de découpe laser haute-énergie / jet d'eau haute-pression couplés. Application à la découpe d'alliages métalliques

Abstract : For a decade, the hybrid jet cutting where a water jet acts as waveguide for the laser has been successfully used in the field of microelectronics. To develop this technology and bring it up to other markets such as automotive, boiler or aerospace, it is necessary to increase both the laser energy and the water jet pressure. At these high energy levels, new interactions that occur between light and fluid as well as the material changes caused by the hybrid jet have never been studied from a physicochemical point of view. So, at first, we have devised a system allowing measurements of optical properties of water at high pressure with a possible direct application in optical sensor for fluid pressure. In an original way, this work has allowed us to measure the refractive index and polarizability of water up to 250 MPa and model their evolution using Tait, Sellmeier and Lorentz-Lorenz equations, respectively. A direct result of this study is the creation of a model linking directly the fluid density to the measurement of its refractive index. Following these developments and after hydrodynamics simulations, we have designed a specific head for coupling a high power laser guided by high pressure water jet. Then we have tested various head types allowing the coupling of a new generation hybrid jet. In the same time, we have studied the physicochemical impact of decoupled hybrid jet where the laser and water jet are both focused, for cutting, at the surface of 301L steel and titanium alloy TA6V samples. The analysis have been done by Raman spectroscopy, X-ray diffraction (XRD), optical microscopy and scanning electron microscopy coupled with EDS (Energy Dispersive Spectroscopy) analysis and the crystallographic orientation (EBSD) analysis. During cutting, a phase transformation and an oxidized layer appear on the surface of the samples. We have shown in particular that these oxide layers and cutting residues are mainly composed of magnetite (Fe3O4) and rutile (TiO2)
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Laurent Weiss. Contribution au développement d'un procédé de découpe laser haute-énergie / jet d'eau haute-pression couplés. Application à la découpe d'alliages métalliques. Autre. Université de Lorraine, 2013. Français. ⟨NNT : 2013LORR0112⟩. ⟨tel-01750100⟩

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