In deep drawing and drawing of car-body parts the friction conditions have a great influence on process limits, on the robustness of the production process and on the quality of the produced parts. Beside the used lubricant, the friction conditions are influenced by the topography of the sheet metal surface and of the tool surface. Therefore the roughness of these surfaces has to be measured.
It is well established to measure the roughness of sheet metal surfaces with a stylus device. But more and more optical measurement techniques are upcomming. There are for example instruments on the market which can characterize the roughness profile along a line with an infra-red laser beam. Doing this for parallel lines the topography can be plotted in three dimensions. The disadvantage of all those systems is that the samples to be measured have to be cut from the sheet or from the coil and that is not possible to measure directly the surface of heavy forming tools. Furthermore the measuring time is quite long, up to a few minutes.
At the Institute for Metal Forming Technology (IFU) in cooperation with the Institute for Technical Optics (ITO) both of the University of Stuttgart - Germany, a new optical measuring device called “IFU/ITO-TopMess” was developed. This is a portable sensor linked to a PC with a special software. This allows the measurement of sheet surfaces as well as the measurement of tool surfaces directly in the press shop. The measuring time is less than one second.
Together with the automotive industries and european steel suppliers new three-dimensional roughness parameters have been developed for describing the microstructure of sheet metal surfaces. These new parameters correlate more closely with the frictional behaviour than the usual measured two-dimensional roughness parameters. Results from laboratory tests and from investigations in press shops demonstrate this correlation.