Influence of tribology size effect on Stribeck curve in micro deep drawing

Bremer Institut für angewandte Strahltechnik GmbH, 28359 Bremen, Germany

^a Corresponding author: e-mail: tetzel@bias.de

Abstract

The lubricant viscosity is one parameter for optimizing drawing processes. The influence is due to the velocity depending friction behaviour between work piece and tool, as well as the effective process forces and resulting pressures in the lubricant. Because of the tribological size effect, the knowledge gained in macro processes cannot be transferred directly to micro forming processes. To understand the influence of the drawing speed, several parameters as the drawing radius and viscosity of lubricants are varied in this work. The resulting Stribeck curves show a varying effect of the different kinematic viscosities. High viscosity lubricant reduces the occurring friction significantly at low Stribeck numbers, but increases friction with rising Stribeck number extremely. Concluding the results, it can be stated that the hydrodynamic friction demands a relevant portion of the overall friction in micro forming process especially at high drawing velocities, which cannot be explained by the lubricant pocket model.