Generating residual compressive stresses in wire drawing for manufacturing highly-stressed torsion springs (DruDraZie)
Final Report Abstract
Aim of the research project was to influence the residual stress distribution over cross-section during wire drawing by geometric elements in the drawing dies. So that generated residual stress conditions in a reproduceable process, which would have a positive effect on manufacture and application of torsion bar springs. First, the material was analyzed. In order to design geometric elements in the dies, FE simulations were set up and specific geometric elements were considered. Based on a wire drawing device was developed and experiments performed. To investigate further processing to torsion bar springs and the influence of the adapted residual stress states of components in the bending process, a modular bending tool was developed. Folding and 3-point bending operations can be analyzed using different bending radii. Based on investigations could be demonstrated that the geometric elements in the dies influence the distribution of the residual stresses over the wire crosssection. The phase-specific residual stresses could be determined by X-ray, depth-resolved and qualitatively verified. Using metallographic and texture analyses, the effect on deformation-induced martensite formation near the surface was evaluated. The geometric elements are able to reduced residual tensile stresses, ideally compressive stresses are generated. The stability of residual stresses was verified in fatigue tests. Results were used to validate the FE simulations and assess the effect to change residual stress distribution on the bending process. In second funding phase the controlled adjustment of residual stresses during the drawing process was intensify. Investigations of relevance of disturbance variables and material fluctuations have been performed. The borehole method, analyze of macro residual stresses, supplement the X-ray analysis. The wires were drawn with the developed drawing dies at different temperatures and drawing speeds. A demonstrator was designed and produced, which has characteristic component areas of a torsion bar spring. The evaluation of the wires was focused on failure and influence of the spring back, and represent a potential improvement of component properties. The FE simulations have been further developed with regard to predictability and investigations into the depiction of phase transformation. In addition material cards for kinematic hardening were prepared. The stability of the residual stresses was quantified and confirmed by dynamic loads in fatigue tests. The interaction between the residual stresses introduced into the wire by the geometry elements and the bending deformation to the torsion bar spring could be investigated in the project and demonstrated with regard to the property formation.
Publications
- Influence of a modified drawing process on the resulting residual stress state of cold drawn wire. MATEC web of Conferences 190, (2018)
Baumann, M., Graf, A., Selbmann, R., Brömmelhoff, K., Kräusel, V., Landgrebe, D., Bergmann, M.
(See online at https://doi.org/10.1051/matecconf/201819004004) - Adjusting the Residual Stress State in Wire Drawing Products via In-Process Modification of Tool Geometries. Materials, (2021), 14, 2157
Baumann, M.; Selbmann, R.; Milbrandt, M.; Kräusel, V.; Bergmann, M.
(See online at https://doi.org/10.3390/ma14092157) - Concept for controlled adjustment of residual stress states in semi-finished products by gradation extrusion. Arch Appl Mech, (2021)
Selbmann, R., Baumann, M., Dobecki, M., Bergmann, M., Kräusel, V., Reimers, W.
(See online at https://doi.org/10.1007/s00419-021-01937-x) - Gezielte Beeinflussung umformtechnisch induzierter Eigenspannungen beim Drahtziehen. Forsch Ingenieurwes (2021)
Baumann, M., Selbmann, R., Dobecki, M., Kräusel, V., Reimers, W., Bergmann, M.
(See online at https://doi.org/10.1007/s10010-021-00501-x) - Strategies for residual stress adjustment in bulk metal forming. Arch Appl Mech, (2021)
Franceschi, A., Stahl, J., Kock, C., Selbmann, R., Ortmann-Ishkina, S., Jobst, A., Merklein, M., Kuhfuß, B., Bergmann, M., Behrens, B.-A., Volk, W., Groche, P.
(See online at https://doi.org/10.1007/s00419-021-01903-7)
