MoVer - Model-Based Distortion Minimization in the Machining Post-Processing of Formed Thick Aluminum Sheets

Initial situation

Due to increasingly complex component geometries and the use of new materials, the qualitative requirements for sheet metal components are rising. During the manufacturing process, the control of distortions in the components in particular is of great importance. Component distortion occurs in almost all manufacturing processes, with casting, 3D printing, forming and machining being particularly important. During the manufacturing processes mentioned, residual stresses can be induced in the component, which in turn can lead to residual stress-induced distortions. The resulting deviations from the desired geometry pose a major problem for the industry, as cost- and time-intensive reworking is necessary. The avoidance of distortions in the individual manufacturing processes is therefore still the subject of numerous investigations. The entire manufacturing process is rarely considered, although the interactions between the individual machining steps, residual stress formation and the resulting component properties are of great importance for a satisfactory machining result.

Objective

In this research project, the residual stresses induced during the forming process are to be taken into account during post-machining in order to minimize component distortion. Currently, one problem in thick sheet forming with machining is the compensation of released residual stresses in the machining process. The released residual stresses lead to component distortion, which is currently compensated for by an additional post-processing step, straightening. However, this leads to a lengthening of the process chain and, accordingly, to higher time and cost requirements for the production of thick sheet metal components that have been post-processed by machining. The research objective of the planned project is to generate dimensionally accurate components after machining by systematically influencing the residual stress state or by a milling strategy adapted to the residual stresses. By deriving general machining strategies to avoid component distortion of machined formed components, the process chain is to be streamlined and the straightening process eliminated.
To achieve the research objective, the residual stresses as well as the residual stress state in the component must be considered over different scales. These include the forming-induced residual stresses, as well as the prevailing residual stress state after forming, the change in the residual stress state due to the geometric removal during machining and the superposition of the existing residual stress state by milling-induced residual stresses.
Based on numerical and experimental results, the influencing variables of the manufacturing processes, such as forming speed, friction, material removal strategy and feed rate on the residual stress state are characterized. With the aid of a broad database, the interrelationships of the influencing variables are analyzed and suitable measures for minimizing component distortion are derived. In contrast to the approaches used so far, which are mostly based on experience, the novel approach is intended to expand the understanding of the process and thus create the possibility of systematically producing dimensionally stable thick sheet components. The research results offer an innovative opportunity to increase efficiency in the production of machined thick sheet components.

Acknowledgements

The research project MoVer is funded by the German Research Foundation (DFG) (project number: ZA288/85-1). We would like to express our sincere thanks for this.