Project Details
Projekt
Generating residual compressive stresses in wire drawing for manufacturing highly-stressed torsion springs (DruDraZie)
Applicants
Dr.-Ing. Markus Bergmann; Professorin Dr.-Ing. Verena Kräusel; Professor Dr. Walter Reimers
Subject Area
Primary Shaping and Reshaping Technology, Additive Manufacturing
Term
from 2017 to 2020
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 372788207
The aim of the project is to influence wire as a starting material for the production of torsion bar springs with the use of specifically modified drawing die geometries in such a way that the different stress distributions formed during the tensile compression forming by wire drawing over the cross-section do not limit the formability of the wire and that bending radii, which cannot be produced with conventionally produced spring wires, can thus be achieved by the remaining residual stresses. Furthermore, the load capacity of the torsion bar springs is to be improved by the adjusted residual stress distribution of the wire. For this purpose, scientific fundamentals have to be worked out so that a targeted design of the internal geometry of the drawing die induces compressive residual stresses in the edge area of the drawn wire, which are advantageous for the component production and, above all, for the later loading behaviour in the application. In the second funding period, the property improvements of the components will be quantified on the basis of the process parameters determined and the process limits for "graduation drawing" from the first phase, and the simulation models will be validated. By means of extensively investigations on the specially developed test facility for wire drawing, it is planned to further optimize the partially differently introduced macro and micro residual stresses on the manufactured semi-finished products with new drawing die geometries for multiple drawing, taking into account the forming speed and temperature during wire drawing. A demonstrator spring is used to evaluate the interaction between the bending process and residual stresses in order to set the residual stress state optimized for the application. For this purpose, the bending tests already started will be continued simulatively and experimentally. In addition, static and dynamic load investigations on the wire products and demonstrator springs are planned in order to evaluate the set residual stress states and the resulting improvement in properties at defined vibration cycles (intervals) and to quantify the stability of the residual stresses. The further development of the measurement and evaluation strategies for the analysis of the microstructure and the macro and micro residual stresses in textured material states and their validation will allow the analysis of the residual stress distribution to be extended. The FE simulations are further validated by the development of a material model, which represents the phase transformation of the material during the forming process and thus improves the property prognoses. Further focal points are the analysis and determination of the relevance of disturbance variables and material fluctuations. The result will be an innovative tool and process concept for the production of torsion bar springs, which are characterized by specifically induced residual stresses.
DFG Programme
Priority Programmes
