Polishing of metallic internal surfaces: technologies, applications, and prospects

The surface quality of metallic internal structures is critical to the performance and reliability of high-end components in fields such as aerospace and biomedical engineering. However, the inherent geometric complexity and limited accessibility of these surfaces pose persistent challenges to polishing. Although recent advances have enriched available techniques, their application remains fragmented, lacking a coherent framework that links surface characteristics, forming processes, and industrial requirements. This review proposes a classification system for internal surfaces and matches appropriate polishing methods to each type, emphasizing their industrial application status. It concludes by outlining future directions aimed at bridging the gap between laboratory innovations and practical deployment.