Fraunhofer-Institut für Produktionsanlagen und Konstruktionstechnik IPK

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  • Publication
    Einfluss von schweißbedingten Rissen auf die Schwingfestigkeit von Widerstandspunktschweißverbindungen aus hochfestem austenitischen Stahl
    ( 2012)
    Brauser, S.
    ;
    Schwenk, C.
    ;
    Rethmeier, M.
    ;
    Noack, T.
    ;
    Jüttner, S.
    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. Die erzielten Ergebnisse weisen nach, dass Oberflächenrisse bis zu einer Tiefe von 0,8 mm (Einzelblechdicke: 1,7 mm) bei den hier geprüften Bedingungen keinen negativen Einfluss auf die Schwingfestigkeitvon widerstandspunktgeschweißtem hochfesten austenitischen Stahl haben. Weiterhin ist nach derzeitigem Kenntnisstand davon auszugehen, dass diese Ergebnisse auf andere hochfeste austenitische Stähle übertragbar sind. Demzufolge können für Bauteile und Baugruppen aus hochfestem austenitischen Stahl im Hinblick auf eine wechselnde Belastung Oberflächenrisse bis zu 0,8 mm zunächst als unkritisch bewertet werden. Inwiefern eine Übertragbarkeit der Ergebnisse auf andere Belastungszustände (Zug-Druck-Wechsel, Scherzug usw.) besteht, ist in weiteren Untersuchungen zu klären. Darüber hinaus weisen die Ergebnisse darauf hin, dass auch eine Spritzerbildung beim Punktschweißen in Kombination mit den resultierenden Schweißrissen nicht zu einer Verringerung der Schwingfestigkeit führt. Vielmehr zeigt sich, dass die Spritzerbildung zu einer Erhöhung der Versagensschwingspielzahlen führen kann, sodass bezüglich der Schwingfestigkeit eine Spritzerbildung ebenfalls nicht als kritisch anzusehen ist. Da sich die hier dargestellten Ergebnisse auf gleichartige Verbindungen beziehen, im Rohkarosseriebau jedoch überwiegend Mischverbindungen, das heißt Schweißverbindungen aus unterschiedlichen Werkstoffen auftreten, ist eine Übertragbarkeit der Ergebnisse beispielsweise auf ferritisch-austenitsche Mischverbindungen in kommenden Untersuchungen zu prüfen.
  • Publication
    Influence of welding-induced cracks on the fatigue strength of resistance-spot-welded joints made of high-strength austenitic steel
    ( 2012)
    Rethmeier, M.
    ;
    Brauser, S.
    ;
    Schwenk, C.
    ;
    Noack, T.
    ;
    Jüttner, S.
    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.
  • Publication
    Influence of Ti and B additions on grain size and weldability of aluminium alloy 6082
    ( 2012)
    Schempp, P.
    ;
    Cross, C.E
    ;
    Schwenk, C.
    ;
    Rethmeier, M.
    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.
  • Publication
    Case study for welding simulation in the automotive industry
    ( 2012)
    Rethmeier, M.
    ;
    Perret, W.
    ;
    Thater, R.
    ;
    Alber, U.
    ;
    Schwenk, C.
  • Publication
    Standards and guidelines for numerical welding simulation
    ( 2011)
    Schwenk, C.
    ;
    Rethmeier, M.
  • Publication
    Different modeling approaches for efficient distortion calculation of an automotive assembly
    ( 2011)
    Thater, R.
    ;
    Perret, W.
    ;
    Schwenk, C.
    ;
    Alber, U.
    ;
    Rethmeier, M.
    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. In this study a MIG welded aluminum assembly from the automotive industry is investigated. Experimental and numerical methods are performed. On the experimental side, temperature cycles are obtained with thermocouples and transient distortion fields are measured using a 3D optical analysis system. On the numerical side, threedimensional nonlinear welding simulations are performed using the welding simulation software simufact.welding to obtain the transient distortion field of the investigated industrial assembly. Several modeling approaches are considered and are discussed with respect to the time-to-solution (modeling effort and the calculation time) and the result accuracy. Finally, a FE model with a good result accuracy and a reasonable calculation time for an industrial application is presented.
  • Publication
  • Publication
    Simulation of inverse heat conduction problems in fusion welding with extended analytical heat source models
    ( 2011)
    Karkhin, V.A.
    ;
    Pittner, A.
    ;
    Schwenk, C.
    ;
    Rethmeier, M.
    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 weld ing of steel plates.
  • Publication
    Efficient welding simulation of an automotive sheet metal assembly
    ( 2011)
    Perret, W.
    ;
    Thater, R.
    ;
    Alber, U.
    ;
    Schwenk, C.
    ;
    Rethmeier, M.
  • Publication
    Simulation of welding temperature field in laser beam welding by inverse techniques
    ( 2011)
    Karkhin, V.A.
    ;
    Pittner, A.
    ;
    Schwenk, C.
    ;
    Rethmeier, M.