8. Roughness measurement

In the case of poorly lubricated crushing, the final surface appears very shiny, reflecting high shear at the tool-tool interface. When crushing is carried out in the presence of a high-performance lubricant, the final surface appearance is matt. Various studies agree that roughness is directly related to the lubrication regime (mixed, boundary, hydrodynamic) during shaping. Indeed, when the lubricant film is thin, the asperities of the part and tools are in contact, leading to a reduction in roughness. On the other hand, with a thick lubricant film, the initial roughness is maintained or increased, as the metal grains are able to rearrange themselves (grain rotation, plastic instabilities leading to surface deformation, etc.).

Surface information is obtained using a roughness meter with a pyramidal diamond tip, the end of which is a spherical cap with a radius...