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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.

Welding processes imply rapid solidification, in presence of high thermal gradient and strong fluid flows in the weld pool. This work presents, in the case of welding, an analysis of the coupling between solidification mechanisms and fluid flows at the macroscale and the microscale. An experimental setup was designed in order to observe in situ a fully penetrated weld pool generated on a Cu30Ni plate with a GTAW torch. At the macroscale, observations are carried out by three cameras: two cameras recording in visible light the top and the back side of the whole weld pool, and one infrared camera catching the thermal field on solid part at the back side. At the microscale, a high-speed camera, mounted with a microscope lens, is used to observe dendritic growth and fluid flows at the back side trailing edge of the weld pool. The observations provide a lot of data allowing analyses and discussions on the correlations between solidification mechanisms and fluid flows, with respect to welding parameters. Then, the experimental results are compared to theoretical results obtained from analytical modelling, in order to discuss the possible limitations of models and try to better understand the coupling between physical phenomena.

The purpose of this article is to investigate the influence of growth kinetic models and nucleation models on the grain structure predicted by cellular automata (CA) during bead on Cu30Ni thin plate. Temperature field is obtained with the computation of two-dimensional finite element model (FE). Based on these temperatures, a CA model simulates the evolution of the envelope of grains along the solidification front. It is shown that for the same temperature field, the grains structure is modified if the growth model changes. The influence of the nucleation law parameters is also discussed from a modelling point of view. Experimental size of the weld pool are compared with thermal results and EBSD maps are compared with grain structure prediction obtained with the CA algorithm.

Wire Arc Addtive Manufacturing (WAAM) is a promising direct energy de-position technology to produce high-value material components with a low buy-to-fly ratio. WAAM is able to produce thin-walled structures of large scale and also truss structures without any support. To manufacture complex parts, process reliability and repeatability are still a necessity and this often leads to long developing times. In this paper, a method is proposed to automatically manufacture complex truss structures with point by point arc additive manufacturing and a six axis robot. Computer aided manufacturing (CAM) software is designed to manage (i) material deposition at intersections and (ii) collisions between the part under construction and the torch. Because it is difficult to model the deposition process, the bead geometry is monitored using video imaging. Image treatment program detects the contour of the deposit and computes its current position. With this position, the CAM software corrects the geometry of the part for future deposition. Simple case studies are tested to validate the algorithm. Two solid free form geometries designed by topology optimization are manufactured with this skeleton arc additive manufacturing process.