Understanding the material flow path of friction stir welding process using unthreaded tools

Material flow during friction stir welding is very complex and not fully understood. Most of studies in literature used threaded pins since most industrial applications currently use threaded pins. However, initially threaded tools may become unthreaded because of the tool wear when used for high melting point alloys or reinforced aluminium alloys. In this study, FSW experiments were performed using two different pin profiles. Both pins are unthreaded but have or do not have flat faces. The primary goal is to analyse the flow when unthreaded pins are used to weld thin plates. Cross-sections and longitudinal sections of welds were observed with and without the use of material marker (MM) to investigate the material flow. Material flow with unthreaded pin was found to have the same features as material flow using classical threaded pins: material is deposited in the advancing side (AS) in the upper part of the weld and in the retreating side (RS) in the lower part of the weld; a rotating layer appears around the tool. However, the analysis revealed a too low vertical motion towards the bottom of the weld, attributed to the lack of threads. The product of the plunge force and the rotational speed was found to affect the size of the shoulder dominated zone. This effect is reduced using the cylindrical tapered pin with flats

Understanding the material flow path of friction stir welding process using unthreaded tools

Material flow during friction stir welding is very complex and not fully understood. Most of studies in literature used threaded pins since most industrial applications currently use threaded pins. However, initially threaded tools may become unthreaded because of the tool wear when used for high melting point alloys or reinforced aluminium alloys. In this study, FSW experiments were performed using two different pin profiles. Both pins are unthreaded but have or do not have flat faces. The primary goal is to analyse the flow when unthreaded pins are used to weld thin plates. Cross-sections and longitudinal sections of welds were observed with and without the use of material marker (MM) to investigate the material flow. Material flow with unthreaded pin was found to have the same features as material flow using classical threaded pins: material is deposited in the advancing side (AS) in the upper part of the weld and in the retreating side (RS) in the lower part of the weld; a rotating layer appears around the tool. However, the analysis revealed a too low vertical motion towards the bottom of the weld, attributed to the lack of threads. The product of the plunge force and the rotational speed was found to affect the size of the shoulder dominated zone. This effect is reduced using the cylindrical tapered pin with flats

Friction stir welding using unthreaded tools: Analysis of the flow

Friction stir welding (FSW) is a solid-phase welding process. Material flow during FSW is very complex and not fully understood. Most of studies in literature used threaded pins since most industrial applications currently use threaded pins. However initially threaded tools may become unthreaded because of the tool wear when used for high melting point alloys or reinforced aluminium alloys. In this study, FSW experiments were performed using two different pin profiles. Both pins are unthreaded but have or do not have flat faces. The primary goal is to analyse the flow when unthreaded pins are used to weld thin (4 mm) plates. Material flow with unthreaded pin was found to have the same features as material flow using classical threaded pins: material is deposited in the advancing side (AS) in the upper part of the weld and in the retreating side (RS) in the lower part of the weld; a rotating layer appears around the tool. The plunge force and the rotational speed were found to affect the thickness of the shoulder dominated zone. This effect is reduced using the cylindrical tapered pin with flats

Etude numérique du procédé de soudage par friction malaxage

Le procédé de soudage par friction malaxage (F.S.W.) est particulièrement bien adapté pour l'assemblage d'alliages d'aluminium. La présente étude porte sur la modélisation thermo-mécanique de ce procédé et sur son implantation dans le code d'éléments finis ABAQUS/Explicit. Un état de l'art est présenté, décrivant diverses écoles traitant de l'effet thermique et mettant en évidence différentes approches basées sur une formulation lagrangienne, eulérienne ou mixte (A.L.E.). Une première modélisation du procédé pour un outil avec pion lisse est ainsi proposée. Les résultats numériques concernent aussi bien le champ de températures que les champs mécaniques au sein de la tôle à souder durant les phases transitoire et stationnaire du procédé. Cette étude a pour but de fournir à long terme un outil prédictif permettant de déterminer les paramètres de soudage à utiliser lors de la mise en œuvre du procédé

Fracture margins for growing cracks in weld repairs

The residual stress field around a single-pass weld filling a slit in a thin rectangular plate has been simulated using both 2D ABAQUS and 3D SYSWELD finite element models, with good agreement between the two codes. Through-wall cracks of varying lengths have been inserted into the plate along the weld centre-line, and the non-linear crack driving force due to residual stress evaluated using three formulations of the J-integral: the standard ABAQUS J, the G-theta approach coded into SYSWELD, and a modified J-integral, J mod, that retains its path independence under non-proportional loading. Cracks were introduced into the FE meshes either simultaneously (all crack flank nodes released in the same step) or progressively (crack opened in small increments from mid-length to tip). The results were compared with crack driving force estimates made using linear elastic fracture mechanics (LEFM) and the R6 procedure. The crack driving forces predicted by all three J-formulations agree well for simultaneous opening, showing that the crack driving force rises to a peak for a crack length equal to the weld length, and falls for longer cracks. Linear elastic fracture mechanics gives a good estimate of the crack driving force for very short defects (confirming the absence of elastic follow up), but is conservative for longer defects, overestimating the peak driving force by 20%. The R6 estimates, which incorporate plasticity corrections, are more conservative than LEFM, overestimating the peak crack driving force by up to 60%. The crack driving force for a progressively opened crack is much lower than for simultaneous opening, indicating that there may be considerable excess pessimism in conventional assessments of defects of this type. Copyright © 2005 by ASME

Mouvement de la matière lors du soudage FSW : Expériences et Simulations

International audienceAfin de diminuer les temps de calculs et coûts de développement, un modèle numérique est développé pour déterminer les paramètres optimaux pour une soudure Friction Stir Welding. La caractérisation du mouvement de la matière doit permettre de qualifier la qualité de la soudure. Une étude de ces mouvements de matière est proposée ici et compare les résultats expérimentaux à ceux issus de simulations numériques sous FLUENT

ENPOWER - Investigations by Neutron Diffraction and Finite Element Analyses on Residual Stress Formation in Repair Welds Applied to Ferritic Steel Plates

The European collaborative research project ENPOWER has as one of its main objectives the development of guidelines for the application of repair welds to safety critical components in nuclear power plants. In this ocntext letter box repair welds applied to thin ferritic steel plates to simulate repair of postulated shallow cracks have been manufactured for the purpose of experimental and numerical analysis of welding residual stresses. Two speciments have been procured, one of them prepared in accordance with a standard welding procedure, while in the second case a different procedure was followed in order to obtain extended martensite formation in th heat affected zone. Residual stresses have been determined in both speciments by neutron diffraction at the HFR of the JRC in Petten, The Netherlands. In parallel Institut de Soudure in France has performed a full 3-dimensional analysis of the residual stress field for the standard welding case taking into account the materials and phase transformations. The experimental data obtained for both specimens clearly suggest that the non-conventional welding procedure rendered higher maximum stress values. In the case of the standard welding procedure numerical and experimental data show a reasonable qualitative agreement. The maximum stress value was in both cases found in the same region of the material - in the base metal justundernaeth the weld pool - and in both cases found to be of similar magnitude (~800 MPa found in neutron diffraction and ~700 MPa found in numerical analysis). In this paper the experimental and numerical approaches are outlined and the obtained results are presented. In addition an outlook is given to future work to be performed on this part of the ENPOWER project. A main issue pending is the application of an optimized advanced post weld heat treatment in one of the two cases and the subsequent numerical and experimental determiniation of its impact on the residual stress field. At the same time further evaluation of the materials transformations due to welding is pursued.JRC.F.3-High Flux and Future Reactor

Simulation numérique du procédé de soudage "friction stir welding"

Des simulations numériques tridimensionnelles sont effectuées afin de déterminer les contraintes résiduelles générées par le procédé `Friction Stir Welding' (FSW). Ces calculs transitoires thermo-mécaniques sont réalisés à l'aide de deux codes aux éléments finis (sysweld et marc). L'apport de chaleur du procédé FSW est modélisé par deux sources de chaleur numériques différentes. Ces sources numériques sont calibrées à l'aide de mesures thermiques expérimentales. Lors du calcul mécanique, l'outil en lui-même ainsi que le flux de matière ne sont pas modélisés. Par contre, les caractéristiques mécaniques de tous les matériaux recristallisés présents dans la structure sont prises en compte dans les calculs. Finalement, des mesures expérimentales de contraintes résiduelles sont comparées aux résultats numériques des deux codes

Numerical Simulations of a Two Roll Round Bar Straightener

peer reviewedA 2-roll bar straightener is a finishing process applied after the rolling operation of round steel bars. During the straightening, the bar rotation is induced by the two rotating rolls. It also undergoes an alternate bending in such a way that the bar section is finally deformed uniformly. The purpose of this process is to correct the curvature defaults of the rolled bar. Indeed, the bar must be straight before being sent to the client and a straightened uniform surface layer is appreciated. With the apparition of new grades and also new diameters of steel round bars, it becomes essential to better understand the straightening process in order to (i) have a better knowledge of what the round bar undergoes during the process, (ii) precisely understand the straightening process, the effect of each component and the process parameters.Stage Flipon master student INSA Rouen Ascometal and ULG LTAS and MS