There is growing interest in additive and subtractive shaping theories that are synthesized to integrate the layered manufacturing process and material removal process. Recently, layer-based machining has emerged as a promising method for integrated additive and subtractive shaping theory. In this paper, major layer-based machining systems are reviewed and compared according to characteristics of stock layers, numerical control machining con®gurations, stacking operations, input format and raw materials. Support structure, a major issue in machining-based systems which has seldom been addressed in previous research, will be investigated in this paper with considerations of four situations:¯oating overhang, cantilever, vaulted overhang and ceiling. Except for the¯oating overhang where a support structure should not be overlooked, the necessity for support structures for the other three situations is determined by stress and de¯ection analysis. This will be demonstrated by the machining of a large castle model.
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