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Der Hauptaspekt der vorliegenden Dissertation ist die Sensitivitätsanalyse der FE- Schweißsimulation, basierend auf einer Variation der Werkstoffkennwerte, sowie deren Einfluss auf das transiente Temperaturfeld und die Verzüge. Dabei wird das Streuband der Werkstoffkennwerte für den gesamten Temperaturbereich sowie für diskrete Temperaturintervalle, die aus der Metallurgie und den experimentellen Randbedingungen abgeleitet sind, betrachtet. Die Untersuchung findet an drei verschiedenen Legierungen statt, welche zurzeit gebräuchliche Werkstoffe im Automobilbau innerhalb der folgenden Hauptlegierungsgruppen darstellen: • hochfester Dualphasenstahl • austenitischer Chrom-Nickel-Stahl • aushärtbare Aluminiumlegierung Die betrachteten Kennwerte sind Wärmeleitfähigkeit, spezifische Wärmekapazität und Dichte sowie E-Modul, Dehngrenze, thermische Dehnung, Querkontraktionszahl und Verfestigungsverhalten. Die Untersuchungen zeigen den großen Einfluss der spezifischen Wärmekapazität und der Dichte auf das berechnete Temperaturfeld und die anschließend ermittelten Verzüge. Mit Blick auf die thermomechanischen Kennwerte werden die Verzüge hauptsächlich von der thermischen Dehnung, dem E-Modul und der Dehngrenze beeinflusst. Die wichtigen thermophysikalischen und thermomechanischen Kennwerte werden für alle drei Legierungen gemessen. Diese sehr genauen Daten werden für eine Simulation ohne die möglichen Fehlerquellen der Streuung der Werkstoffkennwerte verwendet. Die Daten der Werkstoffkennwerte werden dann entsprechend der bekannten Streubänder variiert um die Sensitivität der simulierten Temperaturzyklen und Verzüge zu ermitteln. Die Berechnungsergebnisse werden über Schweißversuche an ebenen Platten mit Laserstrahl- Blindnähten validiert (Thermoelementmessungen, Nahtquerschliffe und Wegaufnehmermessungen der Verzüge). Darüber hinaus werden die Ergebnisse anhand einer Schweißsimulation und Verzugsoptimierung eines industriell relevanten Bauteils überprüft. Die Ergebnisse, Meinungen und Schlüsse dieser Dissertation sind nicht notwendigerweise die der Volkswagen AG.
In diesem Artikel wird eine Übersicht über die Methoden zurnumerischen Berechnung schweißbedingter Bauteilverzüge fürindustrielle Anwendungen gegeben. Zunächst werden die Anforderungen der Automobilindustrie an die benötigte Softwaredargestellt. Dabei wird zwischen der industriellen Forschungund der Entwicklung/Produktionsplanung differenziert. Es werden die verschiedenen derzeit verfügbaren Ansätze zur numerischen Schweißsimulation vorgestellt und deren Möglichkeitenzur Erfüllung der dargestellten Bedürfnisse erläutert. Anhand eines aktuellen Bauteils aus der Automobilindustrie (B-SäuleVW Golf) wird beispielhaft die Verzugsoptimierung mit Hilfe einer Berechnungsmethodik aufgezeigt, welche sich durch eine schnelle Modellerstellung, kurze Rechenzeiten und einfache Handhabung auszeichnet. Ein Vergleich der Simulationsergebnisse mit experimentell ermittelten Daten zeigt sehr gute Über-einstimmungen und verdeutlicht das immense Potenzial einer numerisch unterstützten Prozessoptimierung.
The objective of this paper is to demonstrate a new simulation technique which allows fast and automatic generation of temperature fields as input for subsequent thermomechanical welding simulation. The basic idea is to decompose the process model into an empirical part based on neural networks and a phenomenological part that describes the physical phenomena. The strength of this composite modelling approach is the automatic calibration of mathematical models against experimental data without the need for manual interference by an experienced user. As an example for typical applications in laser beam and GMA-laser hybrid welding, it is shown that even 3D heat conduction models of a low complexity can approximate measured temperature fields with a sufficient accuracy. In general, any derivation of model fitting parameters from the real process adds uncertainties to the simulation independent of the complexity of the underlying phenomenological model. The modelling technique presented hybridises empirical and phenomenological models. It reduces the model uncertainties by exploiting additional information which keeps normally hidden in the data measured when the model calibration is performed against few experimental data sets. In contrast, here the optimal model parameter set corresponding to a given process parameter is computed by means of an empirical submodel based on relatively large set of experimental data. The approach allows making a contribution to an efficient compensation of modelling inaccuracies and lack of knowledge about thermophysical material properties or boundary conditions. Two illustrating examples are provided.
Distortion optimisation of beam-welded industrial parts by means of numerical welding simulation
(2008)
In a previously published model, gas metal arc welding of 1 mm thick DP600 overlap joints is validated for the transient temperature distribution, the welding distortion and longitudinal residual stresses. Tensile tests have been simulated and performed experimentally. Validations were performed for two clamping cases: an immediate release of the clamps after welding and a release of the clamps after cooling to room temperature. There is good agreement between experiments and simulations. It has been found that the temperature distribution, longitudinal stresses and welding distortions are dependent on the clamping conditions. To explain the effect of the clamping time, a bar model is proposed. It is shown that longer clamping times increase plastic deformation and hence reduce residual stresses and buckling distortion. Additionally for an overlap joint, it has been found that the longitudinal residual stresses are affected significantly by the sample's geometry.
Analytical and numerical methods are used to estimate the temperature field due to the heat effects of welding. Numerical techniques are more adapted for industrial complex applications where analytical solutions do not exist yet. However, computational time is much lower with analytical models and a combination of both methods is investigated. Therefore, the two approaches are introduced and confronted in this paper. The finite-element software Ansys has been used for numerical simulations and Scilab for analytical simulations. In order to get a similar result quality, both methods have to be analysed and compared with respect to boundary conditions. These configurations are presented in this paper. Before starting any analysis, the analytical and numerical models have to be comparable. For the numerical simulation, every in- or output is given in discrete form and, for the analytical simulation, in continuous form. Thus, an analysis of the energy input distribution in both models is compulsory to ensure that the same amount of energy is applied. After this first study, a comparison of the analytical and numerical temperature field simulation is done from a fix point source in an infinite volume in steady state to a moving point source in a finite dimension in a transient state. A good agreement between the analytical and the numerical simulation results is found. However, some techniques, like a consideration of an image heat source for the analytical model or the selection of boundary conditions for the numerical model, need to be taken into consideration when the degree of complexity of the study (finite dimension or cooling time) increases. The limit of the comparison is reached when the geometry becomes too complex and when the effect of variable thermal properties with temperature cannot be neglected.
The objective of this paper is to demonstrate a new simulation technique which allows the fast and automatic generation to temperature fields based on a combination of empirical and phenomenological modelling techniques. The automatic calibration of the phenomenological model is performed by a multi-variable global optimisation routine which yields the optimal fit between simulated and experimental weld charcteristics without the need for initial model parameters. For exemplary welding processes it is shown that linear 3D heat conduction models can approximate measured temperature fields with a high accuracy. The modelling approach presented comprises the automatic calibration against multiple experiments which permits simulating the temperature field for unknown process parameters. The validation of this composite simulation model is performed for exemplary welding processes and includes the prediction of the fusion line in the cross section and the corresponding thermal cycles.
Fast temperature field generation for welding simulation and reduction of experimental effort
(2009)
The quality of welding processes is governed by the occurring induced distortions yielding an
increase in production costs due to necessary reworking. Especially for more complex specimens
it is difficult to evaluate the optimal configuration of welding sequences in order to
minimise the distortion. Even experienced welding operators can solve this task only by trial
and error which is time and cost consuming.
In modern engineering the application of welding simulation is already known to be able to
analyse the heat effects of welding virtually. However, the welding process is governed by
complex physical interactions. Thus, recent weld thermal models are based on many simplifications.
The state of the art is to apply numerical methods in order to solve the transient heat
conduction equation. Therefore, it is not possible to use the real process parameters as input
for the mathematical model. The model parameters which allow calculating a temperature
field that is in best agreement with the experiments cannot be defined directly but inversely by
multiple simulations runs. In case of numerical simulation software based on finite discretisation
schemes this approach is very time consuming and requires expert users. The weld
thermal model contains an initial weakness which has to be adapted by finding an optimal set
of model parameters. This process of calibration is often done against few experiments. The
range of model validity is limited. An extension can be obtained by performing a calibration
against multiple experiments.
The focus of the paper is to show a combined modelling technique which provides an efficient
solution of the inverse heat conduction problem mentioned above. On the one hand the inverse
problem is solved by application of fast weld thermal models which are closed form
solutions of the heat conduction equation. In addition, a global optimisation algorithm allows
an automated calibration of the weld thermal model. This technique is able to provide a temperature
field automatically that fits the experimental one with high accuracy within minutes
on ordinary office computers. This fast paradigm permits confirming the application of welding
simulation in an industrial environment as automotive industry.
On the other hand, the initial model weakness is compensated by calibrating the model
against multiple experiments. The unknown relationship between model and process parameters
is approximated by a neural network. The validity of the model is increased successively
and enables to decrease experimental effort. For a test case it is shown, that this approach
yields accurate temperature fields within very short amount of time for unknown process parameters
as input data to the model contributing to the requirement to construct a substitute
system of the real welding process.
Fast Temperature Field Generation for Welding Simulation and Reduction of Experimentall Effort
(2009)
Experimentelle und numerische Analyse des Geometrieeinflusses auf den Schweißeigenspannungszustand
(2009)
Die vorliegende Arbeit stellt Untersuchungen im Rahmen eines Forschungsprojektes mit Schwerpunkt in der experimentellen und numerischen Analyse schweißbedingter Eigenspannungen und Verzüge beim Mehrlagenschweißen dar. Das Auftreten von kritischen Eigenspannungszuständen und untolerierbaren Verzügen während des Fertigungsprozesses verursacht durch erforderliche Nacharbeiten, wie z.B. Richten oder Wärmenachbehandlungen, zusätzliche Kosten. Diese Nacharbeiten können vermieden werden, wenn die numerische Schweißsimulation auf der Grundlage von zuverlässigen Berechnungsergebnissen zur Optimierung angewandt wird.
Die Analyse des Eigenspannungszustandes erfolgt an 5 mm dicken Blechen des unlegierten Baustahls S355J2, wobei Stumpfnaht-Verbindungen mittels Metall-Aktiv-Gas-(MAG)-Schweißen ausgeführt worden sind. Im Zusammenhang mit den Experimenten werden sowohl Temperaturzyklen und Eigenspannungen gemessen als auch Schmelzbadgeometrie und Mikrostruktur ermittelt.
Auf der Basis eines experimentell validierten Temperaturfeldes und umfangreichen röntgenografischen Eigenspannungsuntersuchungen erfolgen numerische Strukturberechnungen. Die auftretenden Phasenumwandlungen werden in der Simulation berücksichtigt.
Die Betrachtung verschiedener Blechkonfigurationen gibt den Einfluss der Blechlänge auf das Niveau der entstehenden Eigenspannungen wieder. Es stellt sich heraus, dass sich die Quereigenspannungen in den nahtnahen Bereich mit zunehmender Blechlänge in den Druckbereich verschieben. Dieses Verhalten kann durch die experimentell validierte Struktursimulation des vorliegenden Prozesses numerisch abgebildet werden und schafft somit den Ausgangspunkt für die spätere Berechnung von mehrlagigen Schweißnähten.
Simulation Based Approach for Distortion Analysis and Optimisation of Beam Welded Automotive Parts
(2009)
Simulation based approach for distortion analysis and optimisation of beam welded automotive parts
(2009)
Continuous cooling transformation (CCT) behavior affects the transient state of
material properties employed in a numerical welding simulation, having a direct influence
on the developing stress state. Three different CCT diagrams for S355J2 steel
were employed to understand the influence of variations in CCT behavior on the numerical
calculation of welding-induced residual stresses. The CCT diagrams were
constructed from transformation data contained in the Sysweld software database,
measured dilatometric data from Gleeble experiments, and transformation data calculated
from the JMatPro software. The calculated transverse and longitudinal residual
stress distributions provided a qualitative correction only in comparison to experimental
measurements, with the largest deviation occurring near the weld
interface. Overall, the results indicate a weak dependency of the calculated residual
stresses due to anticipated CCT variations. The most significant effect on the calculated
residual stresses was shown to be related to the proportion of formed martensite.
It is suggested that CCT data of approximate accuracy is sufficient for reliable
calculation of welding-induced residual stresses.
Normen und Richtlinien für die numerische Schweißsimulation - Entwicklungsbegleitende Normung (EBN)
(2010)
Die Schweißsimulation ermöglicht frühzeitige Aussagen über schweißbedingte Phänomene und hilft so, den Entwicklungsprozess zu verbessern. Damit können die Ursachen auftretender Qualitätseinbußen besser identifiziert werden, sodass eine gezielte Vorgehensweise für die Bauteil- und Verfahrensoptimierung möglich wird. Das wirtschaftliche Anwendungspotenzial der Schweißsimulation ist enorm und mit dem der Umformsimulation vergleichbar. Bei unsachgemäßer Anwendung ist das Fehlerpotenzial jedoch sehr hoch, wodurch die Notwendigkeit einer strukturierten und definierten Vorgehensweise verdeutlicht wird. Hiermit werden nicht nur die Zuverlässigkeit und Aussagekraft der Simulationen sichergestellt, sondern auch eine Grundlage zur effektiven Vergleichbarkeit verschiedener Berechnungsprojekte geschaffen. Diese Sicherheit ist sowohl für Auftraggeber als auch für Auftragnehmer wichtig und hilft, die industrielle Anwendung der Schweißsimulation zu unterstützen und ihr Potenzial voll auszuschöpfen.
Distortion optimisation of beam-welded industrial parts by means of numerical welding simulation
(2010)
Mit Ausgabedatum März 2011 ist die Spezifikation DIN SPEC 32534-1 erschienen. Die Spezifikation wurde im DIN/DVS-Gemeinschaftsausschuss NA 092-00-29 AA „Schweißsimulation (DVS AG I 2.1)" des Normenausschusses Schweißtechnik (NAS) im DIN in Zusammenarbeit mit dem Ausschuss für Technik (AfT) im DVS - Deutscher Verband für Schweißen und verwandte Verfahren e. V. nach dem Vornormverfahren erarbeitet.
The non-uniform heat input during the welding process leads to problematic permanent deformations of welded parts. The control of these welding distortions is, with the absence of the knowledge of the fundamental mechanisms responsible for these deformations, an extremely time and cost consuming iterative “trial-and-error” optimization process. The visualization of the involved physical phenomena, like temperature and distortions, .is an indispensable tool to clearly identify these mechanisms in order to adapt the welding parameters and clamping conditions target-oriented. Both experimental and virtual methods exist to obtain these physical data, however the possibilities to visualize them with experimental methods are laborious, expensive and limited in their application. Welding Simulation using finite element analysis (FEA) offers many benefits and has a great potential to reduce the experimental effort. Nevertheless, the industrial application of welding Simulation is not yet established widely because of reservations regarding the computation costs and the resulting accuracy for instance. In this paper, the results of a case study for a welding Simulation with an industrial background are presented. A welded assembly from the automotive industry has been investigated with numerical and experimental methods. A comparison between both methods demonstrates the Potentials of welding Simulation in terms of visualization. Furthermore, the numerical results reveal the possibilities of current resources. regarding calculation time and result accuracy of an industrial applied welding Simulation.
The usage of continuous cooling transformation (CCT) diagrams in numerical welding simulations is state of the art. Nevertheless, specifications provide limits in chemical composition of materials which result in different CCT behavior and CCT diagrams, respectively. Therefore, it is necessary to analyze the influence of variations in CCT diagrams on the developing residual stresses. In the present paper, four CCT diagrams and their effect on numerical calculation of residual stresses are investigated for the widely used structural steel S355J2 + N welded by the gas metal arc welding (GMAW) process. Rather than performing an arbitrary adjustment of CCT behavior, four justifiable data sets were used as input to the numerical calculation: data available in the Sysweld database, experimental data acquired through Gleeble dilatometry tests, and TTT/CCT predictions calculated from the JMatPro and Edison Welding Institute (EWI) Virtual Joining Portal software. The performed numerical analyses resulted in noticeable deviations in residual stresses considering the different CCT diagrams. Furthermore, possibilities to improve the prediction of distortions and residual stress based on CCT behavior are discussed.
Welding simulation is a powerful, cost-efficient tool to predict welding induced distortion. Nevertheless, effects on calculation result quality are often unknown, thus, sensitivity analyses should be performed to evaluate the influences of certain parameters on distortion development.
In the present paper, a single-layer gas metal arc (GMA) weld of 5 mm thick structural steel S355J2+N is experimentally and numerically investigated. Subsequent to welding, the numerical modeling begins with a mesh analysis based on modal analyses. Hereby, the influence of different coarsening methods and element edge length (EEL) in welding direction on the deformation behavior or the stiffness of the discrete geometry is the focus of the analysis. Secondly, phase transformations in structural steels such as S355J2+N are decisive for final product properties. The sensitivity of welding-induced distortion is examined regarding different continuous cooling transformation (CCT) diagrams for S355J2+N.
The present investigations deal with different relevant influences on numerical calculation of welding-induced distortion. The quality and quantity of these effects are clarified based on the experimental and numerical set-up employed. Consequently, prediction of welding-induced distortion is possible and potential for pre-production optimization is present.
For differentiating the applicability of various numerical welding simulation methods as well as unifying the prerequisites and the steps to be taken in simulation, normative codes are required for the user. Since any standard-like documents are currently still lacking in this field, the DIN German Institute for Standardization in partnership with the Research Association of DVS German Welding Society have set up a standards committee dealing with the preparation of respective documents.
This article focuses on the presentation of the new DIN Spec 32534-1 explaining the major simulation steps and specifying the application fields and the key terms of welding simulation. In addition, a generally valid simulation structure has been established which is intended to serve as a recommendation for customers and suppliers in formulating and handling a service order as well as for persons who start doing welding simulation for the first time. It additionally gives an overview of the other subject areas dealt with in the standards committee as well as of the international activities in this field.
During welding, residual stresses build-up created by the steep thermal gradient that occurs in the weld zone from localized heating and cooling, and phase transformations appearing in low-alloyed structural steel is inevitable. Welding of rather simple test plates do not cover the actual structural effects, which have to be considered during real component welding. However, the resulting welding-induced residual stress state is highly influenced by the structural characteristics, i.e. restraint conditions, of the welded construction. Therefore, a unique large-scale testing facility providing a specific shrinkage restraint while welding and subsequent cooling was used for the present investigations. Hereby, a six bead multi-pass gas metal arc weld of 20 mm thick structural steel S355J2 + N was welded under shrinkage restraint. The residual stresses were experimentally and numerically investigated, and compared to an analysis of plates welded under force-free support and free shrinkage conditions.
The experimentally determined and calculated residual stresses using both 2D and 3D numerical models are in a good agreement. Furthermore, the influence of a shrinkage restraint on the residual stress distribution is both experimentally and numerically shown for the present test set-up.
Welding is a key technology in the area of industrial production due to its flexibility and efficiency. However, new materials and welding techniques necessitate permanent research activities in order to keep up with the demands. A detailed knowledge about the process itself and the heat effects of welding, e.g., temperatures, distortions, and stresses, is the basis for a target-oriented optimization instead of a trial-and-error approach. Numerical welding simulation is a powerful tool to meet these demands. Complementary to an experimental investigation, it enables the analysis of the specimen during the welding process, commonly known as computational welding mechanics (CWM). Whereas simulation is nowadays a common tool in different development processes, the modeling of welding still remains difficult because of the multiple physical effects taking place. One of the most important problems for the user is the lack of knowledge about the material properties as input data for the simulation. Furthermore, any scattering of the data causes uncertainties that can have major effects on the calculations. The objective of this paper is to give an overview about the experimental determination and analysis of the material properties needed as input data for a welding simulation. The measurement techniques and the occurring deviations of the results are discussed. Additionally, the collected data for three representative alloys (dual-phase steel, austenitic steel, precipitation-hardenable aluminum alloy) are analyzed. Finally, the temperature-dependent thermophysical and thermomechanical material properties for these three alloys are given in a ready-to-use format for a numerical welding simulation.
Welding is one of the most widely used joining processes in structural applications, like in car body production in the automotive industry. It is well-known that distortions and residual stresses occur during and after the welding process. Many procedures exist to decrease these negative heat effects of welding, but are often coupled with highly cost intensive experiments. For several decades, simulation models have been developed to understand and predict the heat effects of welding and to reduce experimental effort. In the production planning of various Original Equipment Manufacturers (OEM), some simulation tools are already well established, e.g. for crash test, forming or casting simulations. For welding, the demand is high but the implementation of welding simulation software is still not established yet. Welding is a complex process and the development of a flexible simulation tool, which produces good simulation results without expert knowledge in simulation, is not an easy task. In this paper, a welded assembly from the automotive industry has been simulated and compared to experimental data. Temperature fields and transient distortion distributions have been measured with thermocouples and with an optical 3D deformations analysis tool, respectively. The simulation has been run with a commercially available welding simulation software. The simulated temperature fields match the numerical ones perfectly. The simulated distortions are also qualitatively in best agreement with the experimental ones. Quantitatively, a difference of approximately 20 % between the simulated and the measured distortions is visible; this is acceptable considering the simplifications and assumptions of the simulation model. The global time to solution to get these results without expert knowledge in welding simulation was between 4 and 6 weeks, which is a reasonable time frame for an industrial application of welding simulation.
A single-layer pulsed gas metal arc weld of structural steel S355J2+N with a thickness of 5 mm is experimentally and numerically investigated. Two tack welds are considered in the numerical simulation into two different ways. First, the tack welds are represented by elements belonging to the initial material. This implies that the 'tack weld material' was not exposed to any thermal load or phase transformation before actual welding was performed. The weld seam is shortened and there is an influence on the stiffness of the whole structure affecting the calculation result. Secondly, the tack welds were simulated as conducted in the experimental welding procedure. The cases considering tack welding are compared to a simulation neglecting tack welding and to the experimental results.
The influence of tack welds on the calculated welding-induced distortion is clarified and a contribution to an improved simulation-based prediction of welding-induced distortion is possible by modeling tack welding according to the realistic fabrication procedure.
The present investigations cover different relevant influences on the numerical calculation of welding-induced distortion. Therefore, a single-layer pulsed gas metal arc (GMA) weld of structural Steel S355J2+N with a thickness Öf5 mm is experimentally and numerically investigated. The influences of mesh density, tack-welds, and continuous cooling transformation (CCT) diagrams on welding-induced distortion are studied. The quality and quantity of These effects are clarified based on the used experimental and numerical set up. The occurring differences between the investigated cases achieve significant values. Consequently, prediction of welding-induced distortion can be improved considering the present investigations.
Fusion welding is widely used in the automotive industry to join metal structures. It is well-known that distortions and residual stresses occur during and after the welding process. Many procedures exist to decrease these negative heat effects of welding, but are often coupled with highly cost intensive experiments. The implementation of a welding Simulation tool to reduce this very expensive experimental procedures is therefore of high interest. Despite the fact that the automotive industry is a key sector for Simulation procedures, welding Simulation Software is nevertheless not yet widely implemented. This is mainly due to the complexity of the Simulation tools requiring expert users and the resulting high time to Solution.
In this study, a new fast thermo-mechanical Simulation of a complex and large laser beam welded automotive sheet metal assembly with several non linear welds is simulated. Assumptions and simplifications of the complex physical welding phenomenon, which are made to keep the computational cost and the complexity of the Simulation in an industrial frame, are discussed. The calibration time of the phenomenological heat source model has been optimized with a very fast analytical thermal model and the resulting simulated temperature fields match perfectly with the measured ones. Additionally, the user experience and the time-to-solution are kept within a reasonable time frame for arr industrial environment. All Simulation results are validated with experimental results.
Für die Abgrenzung der Anwendbarkeit verschiedener Methoden der numerischen Schweißsimulation sowie für die Vereinheitlichung der Voraussetzungen und der durchzuführenden Schritte bei der Simulation sind normative Regelwerke für den Anwender erforderlich. Da es derzeit noch keine normähnlichen Dokumente auf diesem Gebiet gibt, wurde vom DIN der Arbeitsausschuss NA 092-00-29-A "Schweißsimulation" gegründet, welcher sich mit der Erarbeitung der entsprechenden Dokumente befasst. Dieses Gremium wurde gemeinsam mit dem Gemeinschaftsausschuss FA 12 "Anwendungsnahe Schweißsimulation" der Forschungsvereinigung des DVS initiiert.
Das Ziel der Normungsarbeit im Bereich der numerischen Schweißsimulation besteht in der Erarbeitung einer DIN SPEC, die die Vorgehensweisen bei der Simulation verschiedener Schweißphänomene und -verfahren langfristig standardisieren soll. In einem durch den genannten Arbeitsausschuss bereits vorbereiteten Entwurf der DIN SPEC 32534-1 wurde die Struktur des Hauptdokuments festgelegt. Im Hauptdokument sind die Anwendungsbereiche und die wesentlichen Begriffe der Schweißsimulation spezifiziert. Des Weiteren wurde die allgemein gültige Simulationsstruktur erarbeitet, welche als Empfehlung für den Auftraggeber und den Auftragnehmer bei der Formulierung und Abwicklung eines Dienstleistungsauftrages sowie für den Neueinstieg in die Schweißsimulation dienen soll.
Den Schwerpunkt stellt die Vorstellung der neuen DIN SPEC mit der Erläuterung der wesentlichen Simulationsschritte dar. Im Weiteren wird auf die Klassifizierung der Unterdokumente in Abhängigkeit des Schweißverfahrens und des angestrebten Simulationsergebnisses eingegangen. Schließlich wird ein Ausblick auf die weiteren Themenfelder des Arbeitsausschusses NA 092-00-29-A "Schweißsimulation" sowie auf die internationalen Aktivitäten auf diesem Gebiet gegeben.
This article studies the three dimensional transient weld pool dynamics and the influence of groove angle on welding of low carbon structural steel plates using the ForceArc® process. The deformation of the weld bead is also calculated with an accurate coupling of the heat transfer with fluid flow through continuity, momentum and the energy equations combined with the effect of droplet impingement, gravity, electromagnetic force, buoyancy, drag forces and surface tension force (Marangoni effect). Different angles of V groove are employed under the same welding parameters and their influence on the weld pool behavior and weld bead geometry is calculated and analyzed, which is needed for subsequent calculations of residual stress and distortion of the workpiece.
Such a simulation is an effective way to study welding processes because the influence of all welding parameters can be analyzed separately with respect to heat transfer, weld pool dynamic, and microstructure of the weld. Good agreement is found between the predicted and experimentally determined weld bead cross-section and temperature cycles. It is found that the main flow pattern is more or less the same although the groove angle increases, but it will evoke larger amount of fluid to flow downward to get deeper penetration.
The paper presents bounded volume heat sources and the corresponding functional-analytical expressions for the temperature field. The power density distributions considered here are normal, exponential and parabolic. The sources model real heat sources like the welding arc, laser beam, electron beam, etc., the convection in the weld pool as well as the latent heat due to fusion and solidification. The parameters of the heat source models are unknown a priori and have to be evaluated by solving an inverse heat conduction problem. The functional-analytical technique for calculating 3D temperature fields in butt welding is developed. The proposed technique makes it possible to reduce considerably the total time for data input and solution. It is demonstrated with an example of laser beam welding of steel plates.
This paper presents volume heat sources and the corresponding functional analytical Solutions for the transient temperature field. The considered energy distributions are normal, exponential and parabolic. The method follows the common approach in Computational Welding Mechanics (CWM) to account for the physics of the welding process and the resulting temperature field by phenomenological models for heat conduction. Therefore, the used heat source models are apparent heat sources that incorporate the real heat input as well as the fluid flow in the weld pool and the latent heat connected with phase transformations. The heat source models provide welding characteristics like thermal cycle and Fusion line in the cross section within short computational time. Consequently, inverse techniques on basis of optimisation algorithms enable the adaptation of the models to the experimental data efficiently. Furthermore, the direct evaluation of the energy distribution for the experimental fusion line in the cross section is demonstrated which enhances the numerical optimisation by reducing the number of unknown model Parameters and providing a reasonable initial guess within the model parameter space. The proposed temperature field models are validated with real laser beam welding experiments.
The results of numerical welding simulations strongly depend on its temperature field. In the present paper, the temperature field of a pulsed gas metal arc weld of structural steel S355J2+N (ASTM A572 Gr. 50) with a thickness of 5 mm is experimentally and numerically investigated. In the case of temperature field validation, volumetric Gauss and double-ellipsoid Goldak heat sources are applied. Additionally, different heat source configurations, including adaptations of thermal conductivity, are analyzed regarding their influence on the calculation of welding-induced distortion.
The investigations clarify the influence of heat source configurations on the calculated results, thus, contribute to an improved prediction of welding-induced distortion.
Kornfeinung im Schweißgut kann die mechanischen Eigenschaften der Schweißnaht und die Schweißeignung des Grundwerkstoffs deutlich verbessern. Eine Möglichkeit korngefeintes Schweißgut zu erreichen, ist das Versetzen des Schmelzbades mit kornfeinenden Mitteln. In dieser Studie wird gezeigt wie Titan- und Borzusätze Korngröße und -struktur von WIG-Schweißnähten der Al-Legierung 5083 (Al Mg4,5Mn0,7) beeinflussen. Dazu wurden in einem Gießprozess stäbchenförmige Einlagen hergestellt, die aus Grundwerkstoff und definierten Zusätzen der Kornfeinungslegierung Al Ti5B1 bestanden. Sie wurden als Ersatz für einen Schweißzusatzwerkstoff in einer Nut im Grundwerkstoff untergebracht und im WIG-Verfahren überschweißt. Durch die Steigerung des Titan- und Borgehalts im Schweißgut konnte dessen mittlere Korngröße deutlich verringert werden. Außerdem wurde eine Änderung der Kornstruktur beobachtet. Die Ergebnisse können als Grundlage genutzt werden, um die empfohlene chemische Zusammensetzung von Schweißzusätzen für Lichtbogenschweißen von Aluminium anzupassen.