It is estimated that 23% of the global energy consumption is attributable to friction between surfaces and subsequent wear. Accordingly, improvements in the tribological characteristics in industrial procedures hold considerable promise. The modification of tribological performance within the context of forming operations using texturing is a common objective. Therefore, in this research project, deterministic semi-finished product textures are systematically designed for specific load cases in order to achieve an improvement in friction, wear and lubrication properties in the subsequent forming process. This will provide a wide range of users with a simple tool for resource-efficient processes.

Motivation

Germany is both the largest producer and the largest purchaser of sheet metal products in the EU. The manufacturing processes are diversified, the machinery is diverse, the energy required for production throughout the country is high, but the raw material is always the same: Sheet metal.

Research work and projects at the PtU have shown that the required friction force can be significantly reduced compared to industrial standards through the targeted texturing of metallic surfaces. Different textures qualify for different tribological load collectives. The aim of this project is to systematically analyze the rheological mechanisms acting through the structure by means of numerical simulations, to identify suitable structures for different processes (deep drawing, profiling, bending) and finally to transfer the deterministic topography to sheet metal. This means that existing production lines and value chains can be made significantly more resource-efficient through the targeted design of the semi-finished product topography. A microscopic approach reduces the energy required in the downstream production process of the end application by significantly lowering friction coefficients, decreasing tool wear and making concepts such as minimum quantity lubrication accessible to a wide range of users (see Fig. 1).

Approach

In this research project, the requirements of different sheet metal working processes, in particular the specific tribological load spectra of the forming processes, are first defined in collaboration with the comitee. Different areas of application result in varying characteristics, which requires precise knowledge of specific process variables. Based on the operating fields, a parametric CFD model is first set up, which allows a targeted, isolated mapping of the individual parameters. This forms the starting point for a variation and targeted fluid mechanical dimensioning of different micro texturing strategies. The result should be optimal structuring parameters for the previously defined operating fields. Subsequently, a roll stand is modified for use in the structuring of semi-finished products. This includes design measures on the stand as well as an adaptation of the control software so that continuous structuring of sheet metal strips is possible with user-friendly assembly and adjustment of the texturing module. It is also necessary to manufacture structuring rollers. For dimensioning, the incremental structuring process is first modeled using FEA in order to select suitable manufacturing strategies based on the loads acting on the micro-tips from the rolling process. In addition, the FEA will be used to kinematically model the semi-finished structuring strategies based on the combined rolling-stamping process. Due to the superimposed rolling, it may be necessary for the structure on the rollers to differ from the target structure on the semi-finished product surface. Different manufacturing strategies will be considered for the production of the rollers and ultimately four roller sets will be produced. Finally, structured sheet metal strips with the desired specification will be produced. Suitable system parameters for structuring will be tested and the service life of the rollers for the different semi-finished materials will be evaluated. This is followed by an evaluation of the tribological properties achieved using the strip drawing test with the load spectra defined at the beginning. Finally, the testing of the properties in the real process is examined using two selected processes.

Acknowledgement

The research work presented here is part of the IGF project no. 01FI23445N of the research association Europäische Forschungsgesellschaft für Blechverarbeitung e.V. (EFB). This is funded by the German Federal Ministry of Economics and Climate Protection (BMWK) via the German Aerospace Center (DLR) as part of the programme for the promotion of joint industrial research (IGF) on the basis of a resolution of the German Bundestag.

We would also like to thank all the industrial partners who support the research project in the project support committee.

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