Additive manufacturing (AM) has become a major manufacturing technology in recent years. In the fused deposition modeling (FDM) method, two-layered parts with a shell structure and an internal structure with gaps are often manufactured. When cutting is applied to such parts, the internal structure is exposed and the surface texture and strength deteriorate. Therefore, it is necessary to remanufacture the parts to correct the shape or fill the inside with resin for additional machining. However, if parts are remanufactured or filled with resin, the amount of material used increases, along with the processing cost and environmental load. If the characteristics of additional machining can be improved, the amount of material used, the processing cost, and environmental load can be reduced. Therefore, in this study, we proposed a shell forming method to form a shell structure by processing the surface of the exposed internal structure with a rod. Shell forming experiments were then conducted to evaluate the characteristics of the method. It was found that the shell thickness can be increased by increasing the shell forming depth, and the difference from the theoretical shell thickness grows larger when the shell forming depth increases. Increasing the rotation speed of the rod was effective in increasing the shell thickness. In addition, as a result of the additional cutting experiment on an AM part, it was confirmed that the properties of the additional cutting surface can be improved using the proposed method.

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