• Mathématiques/Optimisation et contrôle [math.OC]
  
• Sciences de l'ingénieur/Traitement du signal et de l'image [eess.SP]
  
• Informatique/Robotique [cs.RO]
  
• Sciences de l'ingénieur/Mécanique/Génie mécanique
  
• Sciences de l'ingénieur/Mécanique/Mécanique des fluides
  
• Sciences de l'ingénieur/Matériaux
  
• Sciences de l'ingénieur/Mécanique/Mécanique des matériaux
  
• Sciences de l'ingénieur/Génie des procédés
  
• Sciences de l'ingénieur/Mécanique/Thermique
  
• Sciences de l'ingénieur/ Robotique
  
• Physique/Physique/Instrumentations et Détecteurs
  
• Physique/Mécanique/Génie mécanique
  
• Sciences de l'ingénieur/Mécanique/Matériaux et structures en mécanique
  
• Physique/Mécanique/Matériaux et structures en mécanique
  
• Physique/Mécanique/Mécanique des matériaux
  
• Physique/Mécanique/Mécanique des fluides
  
• Sciences de l'ingénieur/Mécanique/Mécanique des solides
  
• Physique/Mécanique/Mécanique des solides
  
• Sciences de l'ingénieur/Mécanique/Mécanique des structures
  
• Physique/Mécanique/Mécanique des structures
  
• Physique/Mécanique
  

Wire Arc Additive Manufacturing (WAAM) is revolutionizing the field of Additive Manufacturing (AM) by being the technological solution to manufacture thin-walled structures of large dimensions and medium geometric complexity at reduced cost with an excellent buy-to-fly ratio. Manufacturing parts with this technology is nowadays done through 2.5D strategies. This type of strategy consists in cutting a 3D model using planar layers parallel to each other. This 2.5D technique limits the complexity of the geometries that can be produced in WAAM without taking advantage of height deposit modulation. It also requires several start/stop phases of the arc during the transition from one layer to another, which leads to poor quality. This paper presents a new fast and efficient path planning strategy aiming at creating a continuous manufacturing path, thus increasing poor part quality. This strategy so called "Scalar Thermal Field for Continuous Toolpath" is generating a continuous spiral manufacturing toolpath for thin shaped parts. The modulation of deposition, by controlling the welding torch travel speed at constant wire feed rate, allows continuous deposition of material throughout the manufacturing process. The keypoint of the method is the use of a thermal scalar field associated with a 6-axis robotic arm kinematics which allows the manufacturing of closed parts after optimal closure point determination or direct manufacturing of opened parts with non-planar free edges. Validation of the presented method is performed by manufacturing three distinct parts : an opened, a closed part and a multi-branch part. The fabrication of these parts and their precise measurement have shown the reliability and the restitution capacity of our method which is clearly superior to 2.5D strategies nowadays commonly used in WAAM technology.

Fluid flow motion controls energy transfer in the weld pool and drives solidification process. Experimental investigation of fluid flow during welding is made particularly difficult by unsteady movements in the molten pool. In this paper, proper orthogonal decomposition (POD) based on images during gas tungsten arc welding (GTAW) on thin plates is used to investigate coherent structures revealed by thermal field in the molten pool. The POD method is based on fluctuating gray levels related to surface temperature. Based on this decomposition, two dimensional spatial modes and temporal coefficients are calculated allowing the identification of regions where temperatures are correlated. To explore the potential of POD method, weld beads were performed on 316L stainless steel plate at three welding speeds (2.3, 3.3 and 4.3 mm.s −1) and constant current (80A). These three conditions lead to different sizes of fully penetrated weld pools and different temperature distributions. Spatial modes and temporal coefficients provide information on temperature fluctuations along the free surface. Based on POD first modes, thermal field is reconstructed along the free surface to understand the heat transfer. Combining these results with side-view observations of the arc allows us to derive three dimensional flow patterns within the weld pool.

Additive Manufacturing (AM) processes enable the reduction of manufacturing time, material waste, and allows for the creation of complex structures. However, anisotropic mechanical behaviour is frequently observed in additively manufactured parts, and it is directly linked to the component's grain structure characteristics, which itself is dependent on the process parameters. The formation of grain structure in 316 L stainless steel fusion lines is investigated in this paper, combining experimental results and numerical simulations. Experimentally, fusion lines are built on a 316 L substrate, using an instrumented LPBF process. The high-speed camera recordings combined with the characterization of the samples enables capturing of melt-pool sizes and grain characteristics. The numerical modelling is based on a three-dimensional “CAFE” model, coupling Cellular Automata and Finite Element models to predict grain formation. The thermal model is defined and calibrated using the experiments. The experimental and numerical grain characteristics are compared. Numerical results are discussed with regards to the growth models and the process parameters. The growth model defined here is compared to existing models and is well fitted to capture grain formation in single-track configurations. Finally, the average grain size and aspect ratio of the grains increase with an increase of the process' linear energy.

Wire arc additive manufacturing (WAAM) is emerging as the main additive manufacturing (AM) technology used to produce medium-to-large-sized thin-walled parts (order of magnitude: 1 m) at lower cost. To manufacture a part with this technology, the path planning strategy used is the 2.5D. This strategy consists in slicing a 3D model into different planar layers parallel to each other. The use of this strategy limits the complexity of the topologies achievable in WAAM, especially those with large variations in curvature. It also involves several start/stops of the arc as it passes from one layer to another, which induces transient phenomena in which the control of the supply of energy and matter is complex. In this article, a new manufacturing strategy to minimize the start/stop phases of the arc to one unique cycle is presented. The goal of this strategy, called "Continuous Three-dimensional Path Planning" (CTPP) is to generate a continuous trajectory in spiral form for closed-loop thin parts. An adaptive wire speed coupled with a constant travel speed allow a modulation of the deposition geometry that ensures a continuous supply of energy and material throughout the manufacturing process. Using the 5-axis strategy coupled with CTPP allows the manufacture of closed parts with a procedure to determine the optimum closing area and parts on non-planar substrates useful for adding functionalities to an existing structure. Two geometries based on continuous manufacturing with WAAM technology are presented to validate this approach. The manufacturing of these parts with CTPP and several numerical evaluations have shown the reliability of this strategy and its capacity to produce complex new shapes with a good geometrical restitution, difficult or impossible to reach today using 2.5D with WAAM technology.

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.