• Ring Compression Test;
  • Oxide Films;
  • Surface Roughness;
  • Coeffcient of Friction

The role of interfaces in friction is most frequently not taken into account when performing the evaluation of the coeffcient of friction by means of process and simulative tribology tests. Despite being diffcult and time consuming to control surface roughness as well as the formation of oxide films through exposure to surrounding medium, it is very important to perform the experiments under conditions similar to those commonly found in real metal forming processes. As accuracy and reliability of the experimentally determined coeffcients of friction depend on the similarity to real metal forming conditions, this paper is aimed to provide a comprehensive analysis on the influence of oxide films and surface roughness in the evaluation of friction by means of the ring compression test. The paper presents an innovative experimental approach for ring compression testing under controlled conditions of exposure to atmosphere and surface roughness. Quantitative data obtained in presence of inert and active gas shields and across typical values of surface roughness allow understanding the role of interfaces in friction and to build a conscience on its prospective source of modelling errors due to experimental drift from real metal forming. Results show an increase of the coeffcient of friction up to 30% when active gas shields are employed.