Simulation and experimental study on form-preserving capability of bonnet polishing for complex freeform surfaces

Bonnet polishing has been widely used in structured surface generation, form correction and surface finishing. The inflated flexible tool is able to match the local surface to realize surface finishing. However, after surface finishing, the polishing induced form change is still not clear, especially for complex freeform surfaces with millimeter-level spatial periods. This paper presents a simulation and experimental study on form-preserving capability of bonnet polishing. The concept of form-preserving capability is discussed firstly. Subsequently, the relative surface speed and contact condition on ripple structures are calculated and analyzed. The results demonstrate that the contact condition of bonnet tool on structured surfaces has the main influence on form-preserving capability. Then, the influence of various factors on contact pressure difference is investigated. Compared with experimental results, the linear correlation between form change and the contact pressure difference is obtained, indicating that form-preserving capability can be strengthened by reducing contact pressure difference. Under optimal conditions, the form change can be controlled less than 20 nm, which proves the superior form-preserving capability of bonnet polishing.