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EfoS – Surface evolution during the production of car body parts

 

Motivation

Developments in sheet metal forming increasingly require a higher information content regarding the sheets used, starting with the delivery condition, through the changes in the manufacturing process to the properties of the final component. While the semi-finished product properties are very well determined by extensive material characterization, there is only very little information content regarding the properties of the formed component, in particular of its surface texture. A derivation of surface properties of the formed part from the semi-finished product properties often coincides with major simplifications. For example the strains induced in the sheet during the forming process lead to a significant roughening of the sheet surface, which is yet to be analyzed and modeled.

 

Objective

The aim of this project is to develop a holistic qualification methodology for body sheet metal forming including the influence of strain on subsequent processes (bondability, corrosion protection, paint appearance). Experimental basis is the development of a laboratory test methodology for the generation of different strain states on large, flat sheet metal specimens. This test method is used to investigate material properties such as deformation-induced surface changes caused by biaxial strains. In addition the relationship between surface changes and the quality of subsequent processes such as paint appearance is analyzed. Furthermore a numerical model will be developed, which is suitable to implement the grain structure of the sheet for the deformation-induced surface analysis. Thereupon software for the qualification of forming sheets will be developed. This software should predict the surface changes of forming sheets as a function of strain conditions and therefore enables the developer to make statements about their post-processing properties.

 

[01] Influence of uniaxial strain on surface topography (left).
Experimental setup for the application of defined strains in flat sheet samples (right).

 

Approach

In close cooperation with the project partners Filzek TRIBOtech and Opel Automobile GmbH an application-oriented, experimental implementation path is being pursued. Filzek TRIBOtech is developing a mechanical forming tool that enables the generation of defined biaxial strains on flat sheet metal specimens.

The PtU primarily focus on the scientific aspect. With the construction of a numerical model, a tool will be created that enables the prediction of strain-induced surface transformation. A high accuracy is to be achieved by the transfer of real grain structures and orientations of the investigated sheet metal.

[02] Schematic sequence of the scientific project focus
[02] Schematic sequence of the scientific project focus
 

Acknowledgment

This project (HA-Project No.: 652/18-75) in the framework of Hessen Modell Projekte, financed with funds of LOEWE – Landes-Offensive zur Entwicklung Wissenschaftlich-ökonomischer Exzellenz, Förderlinie 3: KMU-Verbundvorhaben (State Offensive for the Development of Scientific and Economic Excellence). In addition thanks goes to the project partners Filzek TRIBOtech and Opel Automobile GmbH.