Détermination de cartographies des pénétrations en soudage par laser YAG

Il a été possible d'établir des cartographies permettant de déterminer la pénétration obtenue dans un matériau donné et ce en fonction de quatre paramètres : la puissance moyenne, la fluence, l'irradiance et la durée d'interaction laser-matière. Ces cartographies sont établies à partir d'un calcul numérique monodimensionnel de transfert thermique prenant en compte l'effet de la pression de radiation des photons. Ensuite les évolutions calculées ont été validées expérimentalement grâce à des essais réalisés sur un alliage du type Inconel 690. Ils montrent que deux types de cartographies sont nécessaires, l'une pour les cordons continus et l'autre pour les cordons discontinus (matière solide lors des impacts). La modélisation doit maintenant être développé de façon à obtenir des valeurs de pénétrations plus proches de la réalité dans le cas du soudage avec des puissances élevées (> 1 kW) et des temps d'intéraction plus longs (> 6 ms)

Traitement de surface en continu avec un laser Nd:YAG impulsionnel

This work presents the results of investigations in case of laser cladding with a pulsed Nd:YAG laser. We discuss about the experimental parameters in view to realize single clad and particulary the laser data (energy, frequency, pulse duration). The main results are the clad formation beyond an energy threshold and beyond a threshold pulse duration, the clad behaviour is the same as a clad obtained with a cw laser. Thanks to a cross-section modeling, we compare calculations with experiments and we conclude that the interaction efficiency depends widely on powder spray characteristics

CHARACTERISTICS OF A CW AND PSEUDO PULSED YAG LASER OF 1,2 KW

The main characteristics of the beam are derived from its quality factor (or the Lagrange-Smith invariant). This parameter has been found to vary from 77 to 266 µm, as a function of the beam power, the source functionning mode (CW or pseudo-pulsed), and its transport modalities (throw an optical fiber or throw lenses and mirrors). The maximum power density delivered varies from 0,2 to 2 Mw/cm2. The size of the beam waist after the focalisation system, the depth of the field and the spatio-temporal distribution of the beam energy have also been determined. The knowledge of all these characteristics allows the user to control and reproduce the materials processing by the high power laser beam

INTEREST OF BEAM QUALITY IN MATERIALS TREATMENTS BY HIGH POWER LASER

The aim of the study is the increasing of performances of the YAG Lasers. For this, we use the principle established by Boquillon and Taisne : an X geometry of the resonator. In this case the number of emitted modes is lower than for the linear conception and the beam quality is greater. So, reached power density can be 7 times higher than for the classical cavity and consequently cutting speed can be about 2 times higher than for the linear one. Concerning welding, thick materials need a lot of energy and our system is not competitive. however it exists an interest for thin joining with an easely formed key hole and later a more important penetration

SURFACE TREATMENTS BY Cw YAG LASER

The feasability of surface treatments by cw YAG laser has been established. Concerning solid phasis treatment, we explored superficial quenching of grey cast iron. It brings out that it's no necessar to precoat the sample before treatment, the natural absorptivity is suffisant. Concerning liquid phasis transformation two examples are presented : surface alloying and cladding. For the first one, the power required for a given melted depth is 2 times lower than for a CO2 beam. Concerning the second example, it appears that the use of a step index fiber could ameliorate obtained results. Finally from a metalurgical point of view, obtained structures are the same than with a CO2 beam