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Additive manufacturing (AM) technology enables a new way for fabricating components with complex internal surfaces. Selective laser melting (SLM), being one of the most common AM techniques, is able to fabricate complex geometries with superior material properties. However, due to the poor surface quality, the fabricated internal surfaces cannot meet the specifications for some real applications. To achieve the required internal surface condition, post-polishing process is essential. As one of the most prominent processes for finishing inaccessible surfaces with a wide range of materials, abrasive flow machining (AFM) shows great potential to polish AM internal surfaces. Hence, this paper presents an analytical and experimental study on the internal surface quality improvement of SLM Inconel 718 by AFM, aiming to verify the feasibility of AFM on internal surface quality improvement. The surface evolution process was modeled, and the effects of process parameters on surface and subsurface quality were evaluated. The results show that good surface roughness was obtained at the medium conditions of high viscosity, large particle size, low extrusion pressure, and low temperature. The surface morphology was greatly affected by the medium particle size which showed consistency with the surface evolution model that small abrasive particles are unable to overcome the width and depth of the valleys, resulting in the formation of craters. The partially melt layer was effectively removed, and no subsurface damage was induced.

Magnetic field assisted finishing (MFAF) is a category of non-conventional finishing processes that use magnetic field to manipulate finishing media typically consisting of magnetic particles and non-magnetic abrasives suspended in a carrier fluid. In order to better control the process, an improved understanding of the actual removal process is needed. This paper will introduce a new material removal rate model for magnetic fieldassisted finishing (MFAF) that will aim do so. The model considers the complexity of finishing media used in MFAF processes, where two different types of particles are presented and interact with each other. The proposed material removal rate expression is based on contact mechanics and is a function of the number of active magnetic particles, number of active abrasives, force per magnetic particle, and force per abrasive. Expressions for particle numbers have been developed by considering an ideal facecentred cubic configuration for the magnetic particle network, while expressions for forces have been developed based on a proposed framework for the particle interactions. The model has been verified experimentally for a double-magnet MFAF process by varying the abrasive size and abrasive concentration. When the abrasive size was increased from 0.6 μm to 15 μm, the material removal rate decreased which is consistent 2 with the theoretical trend given by the model. Then, when abrasive concentration, given by the abrasives-to-carbonyl-iron volumetric ratio, was increased from 0 to 0.768, the material removal rate initially increased and then reached a maximum when the volume ratio is 0.259 before decreasing with further increase of the volume ratio. This is also in agreement with the theoretical trend given by the model.

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