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Das Ziel der vorliegenden Vorstudie ist es, die grundsätzlichen Anforderungen, Funktionen und Möglichkeiten vorhandener Software zur Simulation schweißbedingter Phänomene (Prozess-, Struktur- und Werkstoffsimulation) zu erarbeiten und gegenüberzustellen. Die notwendigen Eingabedaten, die vorausgesetzte Anwendererfahrung, sowie die Systemanforderungen und der Rechenzeitbedarf werden für sowohl kommerziell erhältliche als auch zur Zeit noch rein in der Forschung angewandte Programme berücksichtigt.
Nach Aufarbeitung des heutigen Kenntnisstandes der Schweißsimulation wird aktuell verfügbare Software diskutiert. Diese Programme lassen sich in Anlehnung an Radaj in drei Teilbereiche (Software für Struktursimulation, Prozesssimulation und Werkstoffsimulation) unterteilen. Schließlich wird auf notwendige Eingabedaten, hier vor Allem auf die Werkstoffkennwerte, eingegangen. Da die quantitative Aussagekraft der Simulationsergebnisse gewährleistet werden muss, ist eine umfassende Prüfung der Plausibilität und der Genauigkeit der experimentell bestimmten Werkstoffkennwerte notwendig.
Fusion welding processes are widely used for joining metal structures, such as pipes, ships, and cars. In general, these joining processes offer a very good compromise between reliability, safety, cost and maintenance which are important issues in the current economical context. The negative heat effects of welding, i.e. distortions and residual stresses of the welded parts, are well known and many researches in this field have already been done in the last decades in order to minimize them. On the experimental side, many sophisticated procedures have become state of the art to deal with this problem. On the computational side, the improvement of the simulation algorithms and the computing power enables the simulations of many physical phenomena occurring during the welding process. The implementation of welding simulation techniques is nevertheless not an easy task and often associated with expert knowledge which hinders their global application in an industrial environment. This paper is focused on the industrial requirements of a welding simulation software with special respect to the needs of the automotive industry. The necessary information to run a welding simulation and the expectations of a weld specialist without deep knowledge in numerical methods are investigated. These expectations are tested on an automotive welded assembly with a commercially available welding simulation software designed especially for the needs of the automotive industry. A welding experiment is done and the measured temperature distributions and distortions serve as reference to validate the simulation results. The result quality of the simulations of temperature fields and distortions is in best agreement with experimental data. The workflow is well adapted for the considered industrial requirements and the time-tosolution as well as the computational costs are acceptable, whereas the efficient calibration of the heat input model is still a point which will be further investigated in current and future research works.
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.
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.
A goal of industry is to fully map the fabrication process — from the blank metal through the individual fabrication steps all the way to the end product — in a so-called "virtual process chain." The concept of continuous simulation of all relevant fabrication segments is intended not only to achieve a reduction in development and fabrication costs, but most of all to optimize products and fabrication procedures. An essential link in this virtual process chain is welding simulation.
In contrast to other simulation fields like forming simulation, welding simulation is still not widely used in industrial environments. A high user expertise, a high time-to-solution and the result accuracy are the most important problems that hinder its extensively application. Different modeling approaches influence these aspects and an analysis of their implementation is of interest especially for the automotive industry as a key user for production Simulation.
Distortion optimisation of beam-welded industrial parts by means of numerical welding simulation
(2008)
Distortion optimisation of beam-welded industrial parts by means of numerical welding simulation
(2010)
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.
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.
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.
Unter den rauen Bedingungen in der Automobilkarosseriefertigung lassen sich schweißbedingte Imperfektionen wie Risse beim Widerstandspunktschweißen von hochfesten Stählen nicht immer vermeiden. Dabei ist der Einfluss solcher Risse auf die Schwingfestigkeit insbesondere von modernen hochfesten austenitischen Stählen derzeit nicht hinreichend bekannt. Im Rahmen dieser Arbeit wurde daher der Einfluss von Schweißrissen verschiedener Lage und Ausbildung untersucht. Dabei konnte durch die Analyse der normierten Steifigkeitsverläufe von Proben sowie durch die Gegenüberstellung der Versagensschwingspielzahlen nachgewiesen werden, dass die spritzerfrei erzeugten Oberflächenrisse im Zentrum, im Übergangsbereich sowie im Randbereich der Schweißlinse keinen negativen Einfluss auf die Schwingfestigkeit des hier untersuchten hochfesten austenitischen Werkstoffs haben. Proben, die mit Schweißspritzern hergestellt wurden und Risse im Randbereich aufweisen, zeigen deutliche höhere Versagensschwingspielzahlen als rissfreie Referenzproben. ----------------------------------------------------------------------------------------------------------------------------------------------
In the rough conditions in the fabrication of automobile bodies, it is not always possible to avoid welding-induced imperfections such as cracks during the resistance spot welding of highstrength steels. In this respect, the influence of such cracks on the fatigue strength particularly of modern high-strength austenitic steels is not sufficiently well-known at present. The influence of welding cracks with various positions and formations was therefore investigated within the framework of this paper. In this case, the analysis of the standardised stiffness courses of specimens and the comparison of the numbers of failure stress cycles served to prove that the surface cracks produced without any spatter in the centre, interfacial region and peripheral region of the weld nugget do not have any negative influence on the fatigue strength of the high-strength austenitic material investigated here. Specimens which were manufactured with welding spatter and exhibit cracks in the peripheral region show considerably higher numbers of failure stress cycles than crack-free reference specimens.
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.
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.
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
(2011)
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 minimize 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 discretization 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 optimization 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 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)
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.
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.
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, DIN German Institute for Standardization has set up the Standards Committee NA 092-00-29-AA "Welding Simulation" dealing with the preparation of respective documents. This committee was initiated in partnership with the joint committee FA 12 "Weld Simulation on Application" of the Research Association of DVS German Welding Society.
The objective of this Standardization work in the field of numerical welding Simulation is to prepare a DIN SPEC with a view to standardizing the approaches to the Simulation of various welding phenomena and processes over the long run. In a draft version of DIN SPEC 32534 that has already been prepared by the above mentioned Committee, the structure of the primary document was stated. The primary document specifies the application fields and the key terms of welding Simulation. In addition, the 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.
This article focuses on the presentation of the new DIN SPEC 32534-1 explaining the major Simulation Steps. It additionally addresses the Classification of the secondary documents depending on the welding process and on the desired Simulation result. Finally, it gives an overview of the other subject areas dealt with in the Standards Committee NA 092-00-29-AA "Welding Simulation" as well as of the international activities in this field.
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.
Grain refinement is an important possibility to enhance the weldability of aluminium weld metal that is usually defined by its susceptibility to solidification cracking. In this study, grain refinement was achieved through the addition of commercial grain refiner containing titanium and boron to the GTA weld metal of aluminium alloy 6082. The weld metal mean grain size could be reduced significantly from about 70 µm to a saturated size of 21 µm with a change in grain shape from columnar to equiaxed. The grain refinement prevented the formation of centreline solidification cracking that was present only in welds with unrefined grain structure. A variation of torch speed led to a strong change of solidification parameters such as cooling rate that was measured in the weld metal and the corresponding solidification rate and thermal gradient. The ratio thermal gradient/growth rate (G/R) decreased from 50 K s/mm² (high torch speed) to 10 K s/mm² (low torch speed). However, the variation of torch speed did not change the tendency for solidification cracking. The microstructure of unrefined and completely refined weld metal was compared. The observed change in size and distribution of the interdendritic phases was related to the change in susceptibility to solidification cracking.
In the rough conditions in the fabrication of automobile bodies, it is not always possible to avoid welding-induced imperfections such as cracks during the resistance spot welding of high-strength steels. In this respect, the influence of such cracks on the fatigue strength particularly of modern high-strength austenitic steels is not sufficiently well-known at present. The influence of welding cracks with various positions and formations was therefore investigated within the framework of this paper. In this case, the analysis of the standardised stiffness courses of specimens and the comparison of the numbers of failure stress cycles served to prove that the surface cracks produced without any spatter in the centre, interfacial region and peripheral region of the weld nugget do not have any negative influence on the fatigue strength of the high-strength austenitic material investigated here. Specimens which were manufactured with welding spatter and exhibit cracks in the peripheral region show considerably higher numbers of failure stress cycles than crack-free reference specimens.
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.
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.
Die Kornfeinung beim Schweißen ist mit einem Übergang von groben, stängeligen Körnern zu kleineren, globulitischen Körnern im Schweißgut verbunden. Die Feinung der Korngröße und Form führt sowohl zu einer wesentlichen Verbesserung der Schweißeignung als auch zu verbesserten mechanischen Eigenschaften. Heute gebräuchliche Schweißzusatzwerkstoffe enthalten zum Teil bereits geringe Mengen kornfeinender Zusätze, deren Wirksamkeit jedoch von einer Reihe weiterer Randbedingungen abhängt. Durch Zugabe definierter Mengen an Keimbildnern (AlTi5B1) in das Schmelzbad wurde die Abhängigkeit der Korn-größe und –form vom Titan/Bor-Gehalt untersucht. Weiterhin wurde der zur vollständigen Kornfeinung notwendige Mindestgehalt an Keimbildner für unterschiedliche Legierungen und unter unterschiedlichen Schweißbedingungen, sowohl beim WIG-Schweißen als auch beim Laserstrahlschweißen bestimmt. Die Ergebnisse zeigen, dass sich die Korngröße im Schweißgut bis auf ein Minimum von ca. 20µm verringern lässt und zugleich der Anteil der globulitischen Körner zunimmt. Der Mindestgehalt an Keimbildner für vollständige Korn-feinung hängt stark von Schweißgeschwindigkeit und Legierungszusammensetzung ab. Der Einfluss der Kornfeinung auf die Festigkeit, Duktilität sowie die Heißrissempfindlichkeit der Schweißverbindungen wird an ausgewählten Bespielen aufgezeigt.
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.
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.
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.