Modellbildung zur Entstehung dynamischer Nahtfehler während des Elektronenstrahlschweißens an Atmosphäre

An operating form of the electron beam with high economic potential is the welding at free atmosphere (Non Vacuum Electron Beam Welding: NV-EBW). The modern, technological NV-EBW systems dispose enough power to perform processes at high speeds. It opens up possibilities for extensive technological applications, for instance, for the welding of aluminium, steel, copper alloys and dissimilar materials. However, the increase of the process speed impairs the quality of the weld seam, mainly due to the dynamic effects in the welding pool like humping and undercuts. These effects are generated by the thermal and hydrodynamic processes in the weld pool at high welding speeds and by the thermocapillary effect. Seen from the existing theoretical models and experimental examinations, the NV-EBW is unexplored until now because of the complicated interaction of different physical mechanisms. A goal of this work consists in the determining of the conditions for the formation of weld seam failures. For this purpose, the influence of process parameters on the appearance of dynamic weld defects and physical processes in the molten pool are investigated using modern measurement techniques and theoretical modelling. A further goal is the transfer of gained insights on the practical NV-EBW process. To achieve these research objectives, detailed theoretical and practical welding examinations were carried out with observation of the weld pool dynamics and evaluation of the weld quality making possible the evaluation of the effect of welding parameter on weld formation. Thereby, the threshold of the welding speed, beam power and its distribution, the material properties and surface coating are of particular interest because they play a crucial role in the formation of humping and undercuts. Furthermore, for the analysis of the weld pool stability and its dynamics, a mathematical model was developed for the explanation of the process of humping formation depending on the weld geometry, which in turn is influenced by welding parameters. Such complex, experimental and theoretical examinations of the weld pool dynamics during NV-EBW and the reasons of the formation of dynamic weld defects were carried out in this work for the first time. This study gives an important results for the development of the non-vacuum electron beam welding process.