Using Taguchi method to optimize welding pool of dissimilar laser welded components

In the present work CO2 continuous laser welding process was successfully applied and optimized for joining a dissimilar AISI 316 stainless steel and AISI 1009 low carbon steel plates. Laser power, welding speed, and defocusing distance combinations were carefully selected with the objective of producing welded joint with complete penetration, minimum fusion zone size and acceptable welding profile. Fusion zone area and shape of dissimilar austenitic stainless steel with ferritic low carbon steel were evaluated as a function of the selected laser welding parameters. Taguchi approach was used as statistical design of experiment (DOE) technique for optimizing the selected welding parameters in terms of minimizing the fusion zone. Mathematical models were developed to describe the influence of the selected parameters on the fusion zone area and shape, to predict its value within the limits of the variables being studied. The result indicates that the developed models can predict the responses satisfactorily

Optimization of different welding processes using statistical and numerical approaches – A reference guide

Welding input parameters play a very significant role in determining the quality of a weld joint. The joint quality can be defined in terms of properties such as weld-bead geometry, mechanical properties, and distortion. Generally, all welding processes are used with the aim of obtaining a welded joint with the desired weld-bead parameters, excellent mechanical properties with minimum distortion. Nowadays, application of design of experiment (DoE), evolutionary algorithms and computational network are widely used to develop a mathematical relationship between the welding process input parameters and the output variables of the weld joint in order to determine the welding input parameters that lead to the desired weld quality. A comprehensive literature review of the application of these methods in the area of welding has been introduced herein. This review was classified according to the output features of the weld, i.e. bead geometry and mechanical properties of the welds

Application of response surface methodology to laser-induced breakdown spectroscopy : influences of hardware configuration

Response Surface Methodology (RSM) was employed to optimise LIBS analysis of single crystal silicon at atmospheric pressure and under vacuum conditions (pressure ~10-6mbar). Multivariate analysis software (StatGraphics 5.1) was used to design and analyse several multi-level, full factorial RSM experiments. A Quality Factor (QF) was conceived as the response parameter for the experiments, representing the quality of the LIBS spectrum captured for a given hardware configuration. The QF enabled the hardware configuration to be adjusted so that a best compromise between resolution, signal intensity and signal noise could be achieved. The effect on the QF of simultaneously adjusting spectrometer gain, gate delay, gate width, lens position and spectrometer slit width was investigated, and the conditions yielding the best QF determined

Comparison of ANN and DoE for the prediction of laser machined micro-channel dimensions

This paper presents four models developed for the prediction of the dimensions of laser formed micro-channels. Artificial Neural Networks (ANNs) are often used for the development of predictive models. Three feed-forward, back-propagation ANN models varied in terms of the number and the selection of training data, were developed. These ANN models were constructed in LabVIEW coding. The performance of these ANN models was compared with a 33 statistical design of experiments (DoE) model built with the same input data. When compared with the actual results two of the ANN models showed greater prediction error than the DoE model. The other ANN model showed an improved predictive capability that was approximately twice as good as that provided from the DoE model

DIRECT METAL LASER SINTERING OF TI-6AL-4V ALLOY: PROCESS-PROPERTY-GEOMETRY EMPIRICAL MODELING AND OPTIMIZATION

DIRECT METAL LASER SINTERING OF TI-6AL-4V ALLOY: PROCESS-PROPERTY-GEOMETRY EMPIRICAL MODELING AND OPTIMIZATIO

Effects of part-to-part gap and the direction of welding on laser welding quality

Engineering & Systems DesignThe use of laser welding has become quite widespread because it can achieve higher productivity than spot welding. This is due to its desirable features, which include high power density, faster welding speed, highly accurate welding, and excellent repeatability. In addition, laser welding can minimize the distortion in heat-affected zones (HAZs), and there is no tooling that wears out or must be changed over. In spite of these advantages, laser welding still causes many problems when used on compositions such as galvanized steel and aluminum alloy. Galvanized steel, for example, is composed of a zinc layer whose physical parameters differ from those of steel as a base material. Zinc vaporizes at a temperature of 907 K, whereas steel begins to melt at 1510 K. This phenomenon causes serious defects in welds because the pressure of zinc is more powerful than that of steel. As a result, a certain manipulable control is needed in order for the zinc coating to be able to evaporate. To prevent this circumstance, the following solutions have been proposed: (i) a de-gassing method that induces the zinc fumes to escape from the part-to-part gap between two materials; (ii) the removal of zinc layers that will be joined together; (iii) a pulsed laser method that minimizes zinc vaporization using a high energy per pulse and a short pulse duration; (iv) a laser hybrid method; and (v) the addition of additional elements to the surface, which form a compound with the vaporizing zinc. Despite these suggestions, applications involving zinc-coated steels are rarely used in the automotive industry because the shapes of the materials to be welded are not always uniform. In this study, we ascertain the effects of the part-to-part gap and the direction of welding on the quality of laser welding. Using a 2 kW fiber laser and galvanized steel sheets (with thicknesses of 1.4 mm and 1.8 mm), our experiments employed lap welding, which has been applied to side members in the automotive industry. The experimental design was used with a 33 factorial design with 3 replications. The three types of welding direction used are ascendance, descendance, and a uniform gap. Based on the experiments, using analysis of variance (ANOVA) it was determined that the direction of welding is an important factor that can affect the weld quality. In addition, the differences between the shear tensile strengths in the ascendance and descendance directions were determined using a t-Test. The maximum shear tensile strength in the ascendance direction was achieved with a laser power of 2000 W and a welding speed of 2100 mm/min, followed by a part-to-part gap of 0.32 mm/min as the steepest ascent method. Moreover, we analyzed cross-sections of sampling specimens, varying the gap differences in order to verify the differences in shear tensile strength based on two different directions of welding.ope

Mechanical and microstructure analysis of AA6061 and Ti6AI4V fiber laser butt weld

Dissimilar metal welding involves the joining of two or more different pure metals or alloys, usually by melting and mixing and often with the addition of filler metal. There are several types of dissimilar metal welds including stainless steel, either as base metal or as filler metals. Dissimilar metal joints have distinctive features because of differences in the chemical composition of base metal and filler material. Their alloying elements will diffuse intensely during welding. The structures near the fusion line are very complex. Despite of great potentiality in aircraft and automotive industries, dissimilar joining of hybrid Al-Ti structures is often challenging because of the unavoidable formation of brittle intermetallic compounds, mixing of molten phases, and significant differences in material properties. In this work, dissimilar 2 mm thickness AA6000 and Ti6Al4V butt joints were produced by shifting an Yb fiber laser beam on the upper surface of the Ti sheet. Neither filler wire nor groove preparation was adopted. Different working conditions and seam shapes were assessed. The welds were characterized in terms of metallurgical and mechanical behaviors

Integrated approach to Wire Arc Additive Manufacturing (WAAM) optimization: Harnessing the synergy of process parameters and deposition strategies

The flexibility of Additive Manufacturing (AM) technologies in the metal 3D printing process has gained significant attention in research and industry, which allows for fabricating complicated and intricate Near-Net-Shape (NNS) geometry designs. The achievement of desired characteristics in Wire-Arc Additive Manufactured (WAAM) components is primarily contingent upon the careful selection and precise control of significant processing variables, including bead deposition strategy, wire materials, type of heat source, wire feed speed, and the application of shielding gas. As a result, optimizing these most significant process parameters has improved, producing higher-quality WAAM-manufactured components. Consequently, this has contributed to the overall rise in the method's popularity and many applications. This article aims to provide an overview of the wire deposition strategy and the optimization of process parameters in WAAM. The optimization of numerous wire deposition techniques and process parameters in the WAAM method, which is required to manufacture high-quality additively manufactured metal parts, is summarised. The WAAM optimization algorithm, in addition to anticipate technological developments, has been proposed. Subsequently, a discussion ensues regarding the potential for WAAM optimization within the swiftly growing domain of WAAM. In the end, conclusions have been derived from the reviewed research work

Prédiction des attributs géométriques du joint de soudure dans le cas de soudage au laser par recouvrement de tôles en acier galvanisé : modèle 3D et réseaux de neurones

RÉSUMÉ: Le soudage au laser est une des techniques d'assemblage qui a révolutionné de nombreux secteurs industriels, y compris le secteur de l'industrie automobile, grâce à sa productivité et à sa flexibilité. En raison de la nature focalisée du faisceau laser et de sa puissance élevée, le soudage au laser se distingue des autres procédés conventionnels par un apport de chaleur, bref et localisé, favorisant la production de soudures étroites profondes et esthétiques avec des vitesses d'exécution pouvant atteindre plusieurs cm/s, une zone affectée par la chaleur très étroite et des distorsions thermiques limitées. Pour faire face aux contraintes de positionnement précis imposé dans le cas de soudage bout à bout et de soudage d'angle, la configuration de soudage par recouvrement s'avère être mieux adaptée pour la fabrication en grande séries. Cependant, le soudage par recouvrement des aciers galvanisés peut être instable et à cause de l'évaporation prématurée du recouvrement du zinc à l'interface des tôles superposées. Des précautions additionnelles sont nécessaires pour mettre en œuvre ce procédé de façon adéquate. Le choix d'un écart optimal entre les tôles à souder combiné à une sélection adéquate des paramètres du laser peuvent résoudre le problème de l'évaporation du zinc et produire des soudures de très grande qualité. Les propriétés mécaniques d'une soudure réalisée au laser découlent généralement de la forme et des dimensions de sa section transversale, qui dépendent elles-mêmes des paramètres du laser et des conditions de soudage telles que la puissance du laser, la vitesse d'avance du faisceau laser, le diamètre focal et l'écart entre les tôles. Pour exploiter efficacement les avantages du procédé, il faut développer une stratégie qui permet de contrôler les paramètres et les conditions de soudage pour obtenir des soudures avec les caractéristiques désirées, sans avoir recours à la lente et couteuse méthode traditionnelle essai-erreur. L'objectif principal de ce projet consiste à développer des modèles prédictifs permettant d'estimer les attributs géométriques du joint de soudure dans le cas de soudage au laser par recouvrement de tôles en acier galvanisé. L'approche proposée combine expérimentation, modélisation numérique, analyse statistique et modélisation par réseau de neurones pour produire le meilleur modèle prédictif possible. Cette approche est structurée en trois phases. La première phase a permis de réaliser une investigation expérimentale du procédé dans le but faire une l'évaluation qualitative et quantitative des effets des paramètres et conditions de soudage sur la variation des caractéristiques géométriques de la soudure. Les expériences ont été réalisées à l'aide d'un laser Nd-YAG 3KW à émission continue selon une planification d'expériences basée sur la méthode Taguchi. La seconde phase a permis de développer un modèle de simulation numérique 3D du procédé de soudage au laser basé sur la méthode des éléments finis dans le but de simuler le comportement du procédé dans des conditions difficiles à réaliser expérimentalement. Le modèle numérique s'appuie sur les équations de transfert thermique en tenant compte des propriétés du matériau dépendant de la température et de l'enthalpie de changement de phase. Le modèle de source de chaleur utilisé a été adapté de manière à modéliser simultanément le soudage en mode conduction et en mode trou de serrure. Les résultats de la première phase ont été utilisés pour la validation du modèle numérique 3D. Dans la troisième phase, on a développé et testé un modèle prédictif en utilisant les réseaux de neurones artificiels. Une large base de données combinant données expérimentales et données de simulation a servi à l'entrainement et à la validation de plusieurs versions de modèles. Plusieurs critères ont été utilisés pour sélectionner le meilleur modèle, pour l'évaluation de la qualité de ses prédictions et sa capacité de généralisation. Les résultats montrent que le modèle obtenu est un modèle de prédiction rapide et robuste présentant des prédictions compat bles avec les mesures expérimentales générant une erreur de prédiction moyenne ne dépassant pas les 7%. -- Mot(s) clé(s) en français : Soudage au laser par recouvrement, laser Nd-YAG, acier galvanisé à faible teneur en carbone, modèles prédictifs, planification d'expériences, méthode des éléments finis, réseau de neurones. -- ABSTRACT: Laser welding becomes more and more popular in many industrial fields, including the automotive industry, thanks to its high productivity and flexibility. Due to the focused nature of the laser beam and its high incident power, laser welding is well-known for its high and fast heat input, localized in a very small area, thus promoting the production of deep narrow and aesthetic welds with speeds of up to several cm /s, a very narrow heat affected zone and limited thermal distortions. To deal with the positioning constraints imposed on butt welding and fillet welding, the overlap welding configuration is best suited for large-scale fabrication, but the welding of galvanized steels in this configuration becomes unstable and requires additional precautions, because of the premature vaporization of the zinc coating at the interface of the overlapped parts. An optimal gap between the parts and a better combination of laser parameters can overcome this situation and produce defect free welds. The mechanical properties of a laser weld seam depend on the shape and dimensions of its cross-section, which themselves depend on the laser parameters and the welding conditions, namely laser power, welding speed, focal diameter and gap. To effectively exploit the benefits of the process, a strategy must be developed to control welding parameters and conditions to achieve welds with desired characteristics, avoiding the slow and expensive traditional test-fail method. The main purpose of this dissertation is to provide a deep understanding of the dependency relationships between welding parameters and weld characteristics. To be able to predict accurately and instantly these characteristics, a three-phase approach is adopted. The first phase is an experimental investigation of the process, its objective is the qualitative and quantitative evaluation of laser welding parameters effect on the variation of the weld geometry. The experiments are planned according to Taguchi method and conducted using a 3KW continuous Nd-YAG laser on specimens of overlapped galvanized steel sheets. The second phase is the modeling of laser welding process using finite element method, to simulate the process behavior under conditions difficult to perform experimentally. The developed model is based on heat transfer equations and considers temperature-dependent properties of the material and phase change enthalpy. A heat source model is adapted to simulate both laser welding in conduction mode and in keyhole mode. The experimental results are used to validate the 3D finite element model. In the third phase, a large database consisting of experimental results and simulation results is used to train and test a predictive model based on artificial neural networks. Several criteria are used to evaluate the prediction quality of the model and its capacity for future predictions. The obtained results showed a perfect agreement with the experimental measurements, the average prediction error observed is less than 7%. -- Mot(s) clé(s) en anglais : Overlap laser welding, Nd-YAG laser, low carbon galvanized steed, predictive modelling, design of experiments, finite elements method, neural networks