Quantitative characterization of the surface topography of cold rolled sheets Ð new approaches and possibilities G.F. Batalha * , M. Stipkovic Filho Department of Mechatronics and Mechanical Systems Engineering, Escola PoliteÂcnica, Universidade de SaÄo Paulo, Av. Prof. Mello Moraes 2231, 05508 900 SaÄo Paulo SP, Brazil Abstract When processing cold rolled metal sheet with modi®ed surfaces textures, the conventional roughness parameters are not suf®cient to characterize aspects such as rolling mill wear phenomena, as well as sheet metal and lacquered surface, regarding their formability and/or gloss degree. Furthermore, metal sheet forming processes are increasingly focused on tribological parameters; where the sheet metal surface topography becomes a characteristic that shows great potential for process optimization. This work presents 3D surface characterization methods, searching on the basis of this characterization a correlation between the surface topography and the tribological behavior as well as the formability of Al 6016-T4 sheets. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Roughness; Friction; Forming; Metal sheet 1. Introduction Better control in metal sheet forming processes still remains a great challenge. After reducing the scatter in mechanical properties, surface defects and lubrication conditions, the surface topography and its effects outstay as characteristics with a great potential for process and product optimization, as well as for the characterization of new processes [1,2]. New techniques are being applied for the surface structuring of metal sheets duringtheir skin-pass rolling,resulting in lower and more stable friction. Due to some unique features of these new techniques, the structures of these news topographies are quite different from those usually applied. Traditional 2D parameters are not appropriated for a sharp characterization of those surfaces, which can be only suf®ciently described in a quantitative base by new 3D surface analysis methods. The authors also tried by ultrasonic techniques an in situ determination of parameters such as the real contact area [3,4] and have investigated the quality control of a metal sheet surface by using correlation and spectral analysis [5]. In the search of new approaches and possibilities for a quantitative characterization of the surface topography of cold rolled sheets, this paper presents 3D surface character- ization methods and uses them to investigate the frictional behavior of an aluminum alloy sheets, looking for a correla- tion with their surface quali®cation parameters. Due to their lower formability, when compared to steel, aluminum alloy 6016-T4 sheets were chosen aiming an improvement of their formability by suitable tribological properties, in this case suitable surface topographies [6±9]. 2. Surface texturing of cold rolled metal sheets In forming processes the sheet surface structures have the functions of the storage, transport and distribution of the lubricant, as well as the take-up and transport of wear particles. In order to ful®ll these functions they can be separated as follows [10]: 1. Stochastic surfaces characterized by a random distribu- tion of non-identical surface elements. 2. Deterministic surfaces characterized by a geometrically regular distribution of identical isolated surface ele- ments that can act as hydrostatic lubrication pockets and take up wear debris. Such surface textures depends on how the rolls are textured. 1. Shot blast: the rolls are textured by blasting them with hard particles. The surface structure has a random nature stochastic). 2. Electric discharge texturing: the rolls are roughened by a small electric discharge similar to the process of spark erosion. The surface structure has a random nature stochastic). Journal of Materials Processing Technology 113 2001) 732±738 * Corresponding author. E-mail address: gfbatalh@usp.br G.F. Batalha). 0924-0136/01/$ ± see front matter # 2001 Elsevier Science B.V. All rights reserved. PII:S0924-013601)00607-0