Finishing is an indispensable technology to ensure surface quality. In recent years, in the field of ultra-precision machining of metal materials, the surface finishing technology of metal parts with complex shapes and cavities has always been a technical problem faced by the industry. Traditional methods such as chemical mechanical finishing, laser finishing and magnetorheological finishing all have the problem of "tool interference". How to obtain a nanoscale super smooth surface with high efficiency without destroying the surface accuracy of metal parts has already become an urgent technical problem that is needed to be resolved in the industry.
Inspired by the envelope principle of tip trajectory in single-point diamond ultra-precision turning, the researchers at Southern University of Science and Technology proposed a surface finishing technology based on the envelope principle of isotropic etching contour: Under the passivation effect of the polishing solution, a passivation film is formed on the metal surface. Under the action of the electric field, the weak position of the passivation film preferentially occurs breakdown discharge. By optimizing the relevant parameters through Arrhenius formula, the breakdown site can achieve an isotropic etching reaction with a controllable density. With the progresses of isotropic etching, the etching pits continue to expand and merge with each other to complete the envelope, and eventually the original rough surface is replaced by the super smooth surface.
According to the above-mentioned finishing principle, the researchers modeled and analyzed the morphological changes and roughness changes of the material surface during the finishing process. At the beginning of finishing, the surface roughness gradually increases due to the formation of etching pits. With the progresses of finishing, the surface etching sites merge with each other to replace the original rough surface, and the surface roughness decreases rapidly. Finally, the initial surface is completely replaced and transformed into super smooth surface. It can be seen from this model that based on the proposed envelope finishing principle, a sub-nanometer super smooth surface can be theoretically obtained.
The etching contour enveloping surface finishing technology proposed by this research avoids the use of rigid tools that are indispensable to traditional polishing processes. Therefore, this technology does not have the problem of "tool interference". In other words, this newly developed technology can actually process metal parts with complex shapes and internal cavity structures with high processing efficiency and leave no residual stress on the surface after processing. In addition, as it can be seen from the processing principle of this technology, etching contour enveloping surface finishing technology is also suitable for most metal materials and has strong versatility. In the future, this technology is definitely expected to be applied in fields such as aerospace and auto parts, and it can also solve the post-processing problems of 3D printing metal parts.