Investigation of residual stress related mechanisms in the process chain of manufacturing cup extrusion products

• Applicant: Professorin Dr.-Ing. Marion Merklein
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 531877349

Residual stresses have a significant influence on the deformation that occurs during subsequent machining of cold-formed workpieces. In the fundamental research project, it was shown that the residual stresses of components can be influenced in general by the process design on the basis of a cold extrusion process. In the presented transfer project, the overall objective is to identify universal residual stress-relevant mechanisms in the manufacture of cup extrusion parts and to use them in industry-oriented process chains to improve the residual stress state of the components. Using a reference process based on the manufacture of an industrially produced coil housing, mechanisms of residual stress generation during the forming process chain are first investigated numerically and experimentally. Furthermore, fundamental functional relationships of residual stress generation during cup extrusion are to be identified. For this purpose, a more in-depth numerical and experimental investigation of residual stress-relevant elementary processes during the forming of round and elliptical cup geometries will be carried out. In order to improve the material efficiency of the overall process, forming with near-net-shape methods is target-oriented. However, this requires the production of cups with small wall thicknesses, which results in both process-related and residual stress-relevant challenges. For this reason, process limits are to be determined with regard to tool load and achievable wall and bottom thicknesses. The limiting factors here, in addition to the tool load, are the occurrence of oil explosions. Based on this, the influences of process-side control variables on the component residual stresses are to be characterized in order to enable the setting of a specific residual stress state. In particular, friction and punch geometry will be the main focus of the investigation. Based on the reference process, cause-effect relationships between existing residual stress states and resulting component distortion during subsequent machining of formed cups are to be identified numerically and experimentally. From this, a stress state to be set during forming will be derived, with which the distortion can be minimized. The findings will be used to develop a design method for the residual stress-sensitive production of cup extrusion components. An ideal variant will be derived from this, which will be used for experimental verification.

• DFG Programme: Research Grants (Transfer Project)
• Application Partner: Bilstein & Siekermann GmbH + Co. KG