Surface roughness evolution law in full-aperture chemical mechanical polishing

Ultra-high precision revolution surfaces are crucial to mechanical components like bearings but are difficult to achieve using conventional machining. Meanwhile, it is challenging to predict the surface roughness evolution law during processing. Accordingly, this study proposed an ultra-precision full-aperture chemical mechanical polishing (CMP) method for processing revolution surfaces. More importantly, a theoretical surface roughness Ra model was established by assuming that the three-dimensional surface morphology can be simplified to twodimensional identical triangles, each peak can be uniformly removed, and the material removal at the valleys can be neglected compared to that at the peaks. The model provides an intuitive understanding of the Ra evolution law during the full-aperture CMP. Interestingly, Ra first decreases parabolically, determined by the initial surface roughness Ra0, the material volume removal rate MRRV, and the polishing time t. Then, it stabilizes. In addition, the theoretical MRRV model was summarized. The cylindrical guiding surface of a bearing was polished with the developed full-aperture CMP method. In 6 min, Ra can be significantly reduced from the initial 201.09 nm to 1.50 nm almost parabolically and stabilizes. Experimental results basically validate the theoretical Ra model, except that a slow decreasing stage appears intermediately because the real surface cannot be perfectly uniform. Additionally, the roundness error RONt is reduced by 34 %. Furthermore, the full-aperture CMP method and Ra model are successfully applied to other revolution surfaces. This study provides mechanistic insight into Ra evolution modelling pertaining to the manufacturing process.