Investigation on the surface topography in polishing using atomic force microscopy.

An investigation was carried out on the surface topography generation in polishing. Hardened tool steel specimens were polished using different parameters and the surface topography was examined using an Atomic Force Microscope (AFM). Measurements using AFM were initially compared to measurements obtained with a stylus instrument and with an optical profilometer. Contour plots were produced and a number of three-dimensional roughness parameters calculated for each surface. A statistical analysis of the results pointed out the most critical parameter with respect to all roughness parameters, for the material and hardness considered in this investigation, to be the grain size. The process parameters polishing cloth, lubricant, speed and pressure were found to have varying statistical significance with respect to the different roughness parameters. The roughness parameters Sa and Sk were found to be good indicators of the effect of varying the process parameters. An investigation was subsequently carried out on the surface topography generation as a function of the polishing time, for different grain sizes. Good reproducibility of the roughness parameters was found in two different specimens series. Most of the parameters' decrease takes place during the first 100-200 seconds of polishing.