Now showing 1 - 10 of 17
  • Publication
    High-power laser beam welding for thick section steels - new perspectives using electromagnetic systems
    ( 2022)
    Rethmeier, M.
    ;
    Gumenyuk, A.
    ;
    Bachmann, M.
    In recent years, it was shown that the introduction of additional oscillating and permanent magnetic fields to laser beam and laser-arc hybrid welding can bring several beneficial effects. Examples are a contactless weld pool support for metals of high thickness suffering from severe drop-out when being welded conventionally or an enhanced stirring to improve the mixing of added filler material in the depth of the weld pool to guarantee homogeneous resulting mechanical properties of the weld. The latest research results show the applicability to various metal types over a wide range of thicknesses and welding conditions. The observations made were demonstrated in numerous experimental studies and a deep understanding of the interaction of the underlying physical mechanisms was extracted from numerical calculations.
  • Publication
    Recommendations for an Open Science approach to welding process research data
    ( 2021)
    Fabry, C.
    ;
    Pittner, A.
    ;
    Hirthammer, V.
    ;
    Rethmeier, M.
    The increasing adoption of Open Science principles has been a prevalent topic in the welding science community over the last years. Providing access to welding knowledge in the form of complex and complete datasets in addition to peer-reviewed publications can be identified as an important step to promote knowledge exchange and cooperation. There exist previous efforts on building data models specifically for fusion welding applications; however, a common agreed upon implementation that is used by the community is still lacking. One proven approach in other domains has been the use of an openly accessible and agreed upon file and data format used for archiving and sharing domain knowledge in the form of experimental data. Going into a similar direction, the welding community faces particular practical, technical, and also ideological challenges that are discussed in this paper. Collaboratively building upon previous work with modern tools and platforms, the authors motivate, propose, and outline the use of a common file format specifically tailored to the needs of the welding research community as a complement to other already established Open Science practices. Successfully establishing a culture of openly accessible research data has the potential to significantly stimulate progress in welding research.
  • Publication
    Shielded metal arc welding of 9%Ni steel using matching ferritic filler metal
    ( 2021)
    El-Batahgy, A.
    ;
    Saiyah, A.
    ;
    Khafagi, S.
    ;
    Gumenyuk, A.
    ;
    Gook, S.
    ;
    Rethmeier, M.
    Motivated by the tensile strength loss of 9%Ni steel arc welded joints made using Ni-based austenitic filler metals, the feasibility of maintaining the tensile strength using matching ferritic filler metal has been demonstrated. In comparison with shielded metal arc welded joint made using Ni-based austenitic electrode ENiCrMo-6, higher tensile strength comparable to that of the base metal was obtained using matching ferritic electrode. Besides, sufficient impact toughness energies with much lower mismatch were obtained for weld metal and heat-affected zone. Welded joint with a lower mechanical mismatching is of considerable importance for achieving acceptable combination of tensile strength and impact toughness. A better combination of these mechanical properties is ensured by applying a post weld heat treatment.
  • Publication
    Avoidance of liquid metal embrittlement during resistance spot welding by heat input dependent hold time adaption
    ( 2020)
    Böhne, C.
    ;
    Meschut, G.
    ;
    Biegler, M.
    ;
    Rethmeier, M.
    Liquid metal embrittlement (LME) cracking can occur during resistance spot welding (RSW) in zinc-coated advanced high-strength steels (AHSS) for automotive production. In this study, a methodological variation of hold time is performed to investigate the process-related crack influence factors. A combination of numerical and experimental investigations confirms, that the extent of heat dissipation and re-heating of the sheet surface can be influenced and thus the degree of crack formation can be controlled in a targeted manner by the parameterisation of the hold time. The temperature and stress history of crack-free and crack-afflicted spot welds are analysed and a conclusion on the borders defining the LME active region is derived.
  • Publication
    Experimental and numerical study on the influence of the laser hybrid parameters in partial penetration welding on the solidification cracking in the weld root
    ( 2020)
    Bakir, N.
    ;
    Üstündag, Ö.
    ;
    Gumenyuk, A.
    ;
    Rethmeier, M.
    The aim of the present study is to investigate the influence of the laser hybrid welding parameters on the solidification cracks in the weld root for partial penetration welding. Welding trials were performed on thick-walled high-strength steels of grade S690QL under the same critical restraint intensity, with a variation of the welding velocity, wire feeding rate, and the focal position of the laser beam. It was ascertained that the welding velocity has a high impact on the solidification cracking phenomenon. A decrease in the welding speed leads to a reduction of the number of cracks in the weld root. The arc power has also a slight influence on the solidification cracking, while the change of the focal position of the laser beam shows also a remarkable effect. Besides, numerical simulation was performed to understand the thermomechanical behavior of the welds for different welding parameters to assist the interpretation of the experimental results.
  • Publication
    Design of neural network arc sensor for gap width detection in automated narrow gap GMAW
    ( 2018)
    Fabry, C.
    ;
    Pittner, A.
    ;
    Rethmeier, M.
    An approach to develop an arc sensor for gap width estimation during automated NG-GMAW with a weaving electrode motion is introduced by combining arc sensor readings with optical measurements of the groove shape to allow precise analyses of the process. The two test specimen welded for this study were designed to feature a variable groove geometry in order to maximize efficiency of the conducted experimental efforts, resulting in 1696 individual weaving cycle records with associated arc sensor measurements, process parameters and groove shape information. Gap width was varied from 18 mm to 25 mm and wire feed rates in the range of 9 m/min to 13 m/min were used in the course of this study. Artificial neural networks were applied as a modelling tool to derive an arc sensor for estimation of gap width suitable for online process control that can adapt to changes in process parameters as well as changes in the weaving motion of the electrode. Wire feed rate, weaving current, sidewall dwell currents and angles were defined as inputs to calculate the gap width. The evaluation of the proposed arc sensor model shows very good estimation capabilities for parameters sufficiently covered during the experiments.
  • 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
    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 production-related gaps on strength properties and deformation behavior of spot welded TRIP Steel HCT690T
    ( 2012)
    Brauser, S.
    ;
    Pepke, L.-A.
    ;
    Weber, G.
    ;
    Rethmeier, M.
    In this study, the influence of production-related gaps on the shear tension strength and fatigue performance was investigated for resistance spot welded TRIP steel HCT690. Furthermore, the local strain distribution in shear tension test was calculated by the digital image correlation technique (DIC). The static shear tension strength was found to be almost independent of gaps up to 3 mm. The maximum local strain in the spot weld region however decreases depending on which sample side (deformed or undeformed) is considered. In addition, it has been ascertained that gaps of 3 mm lead to a significant drop in fatigue life compared to gap-free shear tension samples. This fact could be attributed to decreased stiffness, higher transverse vibration and higher rotation (?) between the sheets as well as increased local stress calculated by 2 dimensional FE simulation.
  • 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.