On the correlation between crystallographic grain size and surface evolution in metal forming processes

Today, there is an obvious trend for implementation of net shape or near net shape forming technology products in nearly all branches of industry. Often, these components underlie specifications in terms of surface quality. However, the surface topology will change during forming operations, and cause an effect called “surface evolution”. Especially in sheet metal forming processes increase in surface roughness, caused by the in plane plastic straining, is frequently observed. Contact loading is capable to decrease surface roughness. In sophisticated forming applications, like deep drawing and ironing of small tubular-like cups the surface evolution is quite dependent on the crystallographic grain size of the workpiece. With respect to this phenomenon, often the question arises whether there is a ratio of surface topology characteristics to grain size constituting the limit of a single grain's influence on roughness evolution. Therefore, in the present work fundamental analyses on the mechanisms governing surface evolution are conducted. The influence of crystallographic grain size and grain orientation on roughening as well as on roughness reduction is shown. Moreover, a correlation between surface topology, grain size and surface evolution is derived.