The effect of tool wear on the removal characteristics in high-efficiency bonnet polishing

In order to figure out the effect of tool wear on the material removal process in bonnet polishing, an experimental study based on the comparison of removal characteristics of bonnet tools with various wear conditions is presented. Before the experiments, the tool surfaces were measured using a digital microscope, and it revealed that not only the surface contour but also the surface topography were changed by tool wear. For this reason, a preprocessing, i.e., a uniformity controlling method for the spot size, was proposed and validated to keep the spot size constant using static stress sensor. Subsequently, the comparative experiments were conducted, and it was indicated that along with the increase of the wear degree of the bonnet tool, the removal shape changed and the peak removal depth, peak removal in unit time, and removal volume reduced significantly, but the roughness of the polished surface becomes better. Based on the results and the analysis, we deduced that the probably causation for the above phenomenon is the variation of the friction between the workpiece and bonnet tool, because of the alteration of the tool surface topography brought by tool wear. Consequently, the forces in the polishing process were measured using a 3-component dynamometer, and the friction coefficient was calculated. The results showed that the variation trend of the friction coefficient is similar to that of the removal volume, i.e., the removal volume and the friction coefficient of the mild wear tool are basically the same to the new tool, but apparently larger than the severe wear tool, which demonstrates that the reduction of the friction coefficient by tool wear is one of the most important reasons for the decrease of the removal efficiency.