Measurement and characterisation of the microtopography in the contact area between workpiece and tool in microforming

Abstract

The forming load in metal forming processes is transmitted from the tool to the workpiece only by a certain fraction of the nominal contact area. According to the mechanical-rheological model, these fractions are mainly the real contact area (RCA) and the so-called closed lubricant pockets (CLP). As the number of these contact area—RCA and CLP—is reduced drastically in micro forming processes due to small part dimensions and approximately scale invariant surface topographies, the influence on the tribological conditions is increased significantly. Therefore, the knowledge about the real contact state in these areas in micro forming is much more important compared to conventional “macro” length scale. In the macro case, the real contact area is regarded as completely flattened during the forming process while the sub-topography, which emerges on single asperities, is not considered. This chapter introduces a test rig for the characterization of the flattening behavior of single asperities by in-situ observation and for the recording of the force-displacement characteristics. It also presents a strategy for the evaluation of the sub-topography on single asperities leading to an improved understanding of the tribological behavior in micro forming processes. Thus, an improved simulative process design of micro forming processes is enabled.