Novel rotating-vibrating magnetic abrasive polishing method for double-layered internal surface finishing

Components with complex internal surfaces are increasingly important for gas and fluid flow applications in aerospace and automotive industries. Recently, as an emerging manufacturing technology, three-dimensional (3D) additive manufacturing (AM) technology enables one-step fabrication of these complex internal surfaces. Although 3D AM technology eliminates the need for complex assembly process, due to the poor surface and sub-surface integrity, achieving a favourable surface condition is challenging. Therefore, a post-polishing process is essential for these 3D AM complex internal surfaces. This paper presents a novel rotating-vibrating magnetic abrasive polishing method to finish a kind of complex internal surface which has a double-layered tube structure made by selective laser melting (SLM) of Inconel 718. The principle of the method was illustrated and the material removal process was modelled. The feasibility of the method was verified and the surface evolution mechanism under different motions was revealed. The effects of process parameters on material removal and surface quality were evaluated quantitatively. The results showed that material was uniformly removed from both of the external surface of inner tube and internal surface of outer tube. The uneven surface caused by partially melt powders during SLM process was smoothed and the surface roughness was reduced from about 7 μm Ra to less than 1 μm Ra. Relatively higher material removal efficiency and lower surface roughness were obtained through combining rotation and vibration motions. The surface quality was improved representing by the increase of surface nanohardness and release of residual stress after polishing. There was no subsurface deformation and damage observed so that a damage-free surface was obtained.