• Sciences de l'ingénieur/Matériaux
  
• Sciences de l'ingénieur/Mécanique/Thermique
  
• Sciences de l'ingénieur/Génie des procédés
  
• Sciences de l'ingénieur/Mécanique/Mécanique des solides
  

Ce document est un rapport d’étude qui présente les travaux effectués par l'équipe Assemblages Soudés (AS) du LMGC (Univ. Montpellier - CNRS, UMR 5508) dans le cadre du projet ANR Nemesis (Projet ANR-17-CE08-0036 du Programme AAPG 2017). Il s’agit d’une étude expérimentale réalisée principalement au cours du post-doctorat de Nicolas Blanc. Le but de cette étude est de pouvoir observer la solidification et le comportement du bain de soudage in-situ pour deux types d’alliages d’intérêt industriel : l’acier 316L et l’acier 22MnB5, intéressant de façon prioritaire respectivement EDF et Arcelor Mittal, partenaires du projet ANR. Les expériences doivent permettre d’obtenir des informations sur la taille et la forme du bain, sur les écoulements existants en son sein et sur le processus de solidification. Pour cela un dispositif similaire à celui utilisé par Alexis Chiocca [1] est utilisé. Le document est organisé autour de quatre chapitres. Le premier est dédié à un succinct état de l’art afin de rappeler le contexte scientifique général et l’utilité des observations réalisées dans la compréhension des phénomènes de solidifications pendant le soudage. Le deuxième chapitre est consacré à la présentation du dispositif expérimental spécifiquement conçu pour ce type de mesures et à la présentation des méthodologies d’étude. Les deux derniers chapitres sont consacrés à la présentation des résultats obtenus respectivement pour l’acier inoxydable 316L et les alliages 22MnB5.

A thermo-mechanical simulation of the wire + arc additive manufacturing (WAAM) process is presented in this work. The simulation consists in the deposition of 5 successive layers of 316 L stainless steel on a 316 L base plate. The thermo-mechanical analysis is solved in two dimensions under plane stress assumption. Nonetheless, the metal addition is taking into account in this numerical analysis. An increment of material is added at each time step. This numerical approach allows reducing the computational time. The temperature and residual stress fields are computed at each time step. Two patterns of deposition strategy are also investigated. It is shown that the longitudinal stress varies mainly along the vertical axis. A sample with 5 overlaid layers has been scanned with neutron diffraction technique in order to measure the final residual stresses. Both numerical and measured residual stresses are in good agreement. The Aster finite element software is employed for the numerical analysis.

4043 aluminium deposits were elaborated using a 3D print device equipped with a Cold Metal Transfer welding source. Two sets of process parameters leading to different average powers were compared in order to establish the relations between the powers and energies produced and the geometrical characteristics of the deposits. The effects of the travel speed and layer superposition on the transfer mechanisms as well as on the geometrical characteristics of the deposits were discussed for both sets of parameters. Finally, the formed microstructures were analysed and the porosity defects were quantified and discussed with regard to the heat input characteristics and the solidification conditions.

WAAM (Wire+Arc Additive Manufacturing) allows manufacturing mechanical components by adding successive layers of molten metallic wire using electrical arc. The WAAM process, compared to other processes using metallic powders, presents some advantages such as: high deposition rate (2-4kg/hour), manufacturing of large scales components and cheaper industrial installations. WAAM is then an interesting candidate for manufacturing components often CNC machined. However, the main disadvantages of this process are: high surface roughness requiring a post machining, strains and stresses states generated during the deposition process [1]. A better understanding of the relation between the welding parameters and the state of stresses can contribute to minimize residual stresses, eventually in relation with a deposition strategy [2]. As a first approach, the effects of the first deposition of molten metal on the base plate is investigated. This work focuses on finite element method, based on Code Aster solver, with a nonlinear thermo-mechanical model. Concerning the thermal aspects, the GMAW heat input is modeled by a Gaussian distribution [3]. The temperature fields are used to solve the mechanical problem. The material behavior laws are assumed to be elastoplastic with different hardening configurations: no hardening, linear isotropic or kinematic hardening and non-linear isotropic hardening. Based on the results from these elastoplastic models, the influence of the hardening is presented.

In this work, two indirect approaches are compared to estimate the efficiency of the cold metal transfer welding process with two different current waveforms. The first approach is based on an analytical heat transfer model coupled with thermocouple measurements. The second method includes numerical heat transfer simulation of aluminium filler on the galvanised steel sheet. Then a diffusional-growth model allows evaluating the thickness of the Fe-Al intermetallic layer that was compared it to that of the experimental one. Results show that both methods give very similar process efficiencies. The process efficiency reaches a high value (0.92) with current wave-forms using high-intensity pulses of short duration, whereas it decreases to 0.78 with current waveforms using low-intensity pulses of long duration.