Compréhension de la formation de porosités en fabrication additive (LBM). Analyse expérimentale de l’interaction laser – lit de poudre – bain liquide.

Abstract : The selective laser melting (SLM) process allows to produce dense metal parts directly from the melting of successive powder layers. However, many technical issues are still to overcome for making SLM a fully viable manufacturing process. This is the case of surface finishing and the systematic occurrence of porosities, which require post machining steps. Up till now, the origin of porosities remains unclear but is expected to be related to the stability of the process. This thesis proposes an original study of the laser-powder-melt pool interaction on 316 L and on two aluminum alloys (5086 and 4047) before studying the material’s densification conditions. The work is structured in two parts. In the first part, an experimental study of the laser-matter interaction has been carried out on an instrumented SLM setup equipped with a fast camera (>10 000 images /s). The conditions of formation of metal ejections, denudation and hydrodynamics of melt pool (including humping) have been characterized and quantified. All these phenomena are related to the high power densities used in SLM, which favor keyhole regime and vaporization. The aim of the second part of this work was to characterize the origin and the porosity fraction on an SLM machine. A first correlation has been made between the dimensions of the fusion beads and the densification conditions. A strong interaction (Rayleigh scattering or absorption) has been observed between the incident laser beam and the nanoparticles contained in the metal vapor column: this interaction is responsible for the significant dispersion of melting depths.
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Valérie Gunenthiram. Compréhension de la formation de porosités en fabrication additive (LBM). Analyse expérimentale de l’interaction laser – lit de poudre – bain liquide.. Mécanique des matériaux [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2018. Français. ⟨NNT : 2018ENAM0028⟩. ⟨tel-02025457⟩

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