Internal surface finishing and roughness measurement: A critical review

Modern industrial equipment is increasingly characterized by miniaturization, integration, and high performance, necessitating the production of complex structural parts with exceptionally high internal surface quality. Direct manufacturing often leads to high internal surface roughness, which traditional finishing and measuring methods cannot adequately address due to the decreasing size and increasing complexity of internal structures. This is especially true for components like pipes with large aspect ratios, extremely small deep holes, multi-stage bends, cross pipes, and array holes. To meet the high-performance manufacturing demands of these parts, advanced internal surface finishing and roughness measurement technologies have gained significant attention. This review focuses on the challenges and solutions related to internal surface parts with various apertures and complex structures. Internal surface finishing methods are categorized into mechanical finishing, fluid-based finishing, and energy-field-based finishing based on their characteristics. Roughness measurement technologies are divided into tool-probing and non-probing methods. The principles, required equipment, and key parameters of each finishing and measurement approach are discussed in detail. Additionally, the advantages and limitations of these methods are summarized, and future trends are forecasted. This paper serves as a comprehensive guide for researchers and engineers aiming to enhance the internal surface quality of complex structure parts.