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Knowledge based process development of bobbin tool friction stir welding
Citation Link: https://doi.org/10.15480/882.1069
Other Titles
Wissensbasierte Prozessentwicklung des Rührreibschweißens mit Bobbin Tool
Publikationstyp
Doctoral Thesis
Date Issued
2012
Sprache
English
Author(s)
Advisor
Title Granting Institution
Technische Universität Hamburg
Place of Title Granting Institution
Hamburg
Examination Date
2012-07-17
TORE-DOI
Over the last twenty years Friction Stir Welding (FSW) has proven to be a very promising new joining technique. Especially high strength aluminium alloys can be welded with large advantages as compared to conventional fusion welding processes. For some joint configurations and desired applications bobbin tool welding is a process variant that can circumvent limitations arising from the high process forces in conventional tool FSW. As bobbin tools are highly mechanically loaded, in-depth understanding of the evolution of temperatures and forces is desirable to avoid tool failure and extend the range of applicable process parameters together with overall productivity. Up to now the process and tool development has been mostly empirical. A transition to a science based approach is highly necessary.
The work presented here was conducted to establish a set of numerical models that can be used in process development of bobbin tool FSW. The first model covers the transient temperature fields that are needed as input for any further model. The material flow model predicts the acting forces and shear layer shape. Finally the mechanical loads on the tool are predicted by a mechanical model.
The models predict very time and position dependent conditions for the investigated specimen sizes and welding speeds. This explains the instability that can be observed experimentally under certain conditions. A control strategy is needed to produce sound welds at reasonable productivity. A versatile controller has been successfully designed, implemented and tested as part of the work presented here.
The models are applied to the existing tools and validated experimentally. A novel tool design is developed based on the experimental results and further improved using the models predictions. Finally the new tool design is tested. The results have shown that the productivity of the process as well as the joint quality could be significantly improved. The knowledge about the thermal history and extent of plastic deformation gained from the process model is a valuable input to the understanding of microstructure formation and the development of residual stress fields.
The work presented here was conducted to establish a set of numerical models that can be used in process development of bobbin tool FSW. The first model covers the transient temperature fields that are needed as input for any further model. The material flow model predicts the acting forces and shear layer shape. Finally the mechanical loads on the tool are predicted by a mechanical model.
The models predict very time and position dependent conditions for the investigated specimen sizes and welding speeds. This explains the instability that can be observed experimentally under certain conditions. A control strategy is needed to produce sound welds at reasonable productivity. A versatile controller has been successfully designed, implemented and tested as part of the work presented here.
The models are applied to the existing tools and validated experimentally. A novel tool design is developed based on the experimental results and further improved using the models predictions. Finally the new tool design is tested. The results have shown that the productivity of the process as well as the joint quality could be significantly improved. The knowledge about the thermal history and extent of plastic deformation gained from the process model is a valuable input to the understanding of microstructure formation and the development of residual stress fields.
Subjects
FSW
Simulation
Process
Bobbin tool
DDC Class
620:Engineering and allied operations
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Dissertation_J_Hilgert_2012_online.pdf
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