【正文】 idered are:SDM is a multistage process: Multistage processes require or should allow multiple processing stations and transfer of parts between stations. An industrial SDM shop needs to determine scheduling of parts and operations, floor layout, assignment of jobs to machines, soon as multiple machines are considered, the manufacture of several parts will want to take advantage of parallel processing in different stations to maximize equipment utilization. Each part can be built following several alternative sequences. The execution system should be able to take advantage of this flexibility to optimize cost and turnaround execution system should coordinate activities of machines and transfer of parts, and track and balance the state of load of each machine in the shop to achieve a smooth flow.These characteristics make the process somewhat similar to VLSI manufacturing, where an array of processes work in sequence to produce a wafer. A wafer，route travels through a variable number of machines depending on its process plan, and it is very cyclic (LithographyEtchImplant). In a similar fashion to VLSI manufacturing, the execution system will have to cover the handling of partially built parts and intermediate planning takes full 3D geometric models as inputs and outputs process description that specifies contents and sequences of operations that are necessary to produce the input parts. The contents contain machineunderstandable codes for driving designated machines to perform desired operations where as sequences specify all possible orders of operations that are valid to manufacture the input parts.Basic planning steps involve determining building directions, deposing a part into manufacturable volumes (called singlestep geometry), representing these submodels in a structured format for allowing optimizing building sequences, depositing materials on each singlestep geometry, and shaping deposed entities. The goals of these tasks are to generate process plans that are of lowcost, highquality, highprecision, and fast turnaround time. We will first define the constituent of the additive/subtractive process: singlestep geometry.Additive/subtractive SFF processes involve iterative material deposition, shaping and other secondary operations. Each of such operations is associated with a part ponent or a deposed geometry, which together represent a final product. The characteristics of such deposed geometry (a set of singlestep geometries) are that all supports for its undercut features are previously built, and no interference should occur in depositing or shaping processes from the top with respect to the building direction. In other words, any ray cast along the growth direction should not intersect a singlestep geometry more than once.Operations associated with each singlestep geometry may include deposition with different types of material or machines, machining operations using CNC machines, or electrical discharge machining. Or it could be simple operations such as automatic insertion of prefabricated following describes issues related to automatic and optimal planning for additive/subtractive approaches are not dissimilar with other pureadditive SFF processes in determining building directions. However, there are some more issues to be considered for additive/subtractive processes:The number of deposed singlestep geometries reflects time for part building. In a typical additive/subtractive process, shaping operations usually need deposited materials to be conditioned (in the case of plastics, cured/hardened。 in the metal cases, cooled). The more the steps, the more the building time is consumed in the conditioning procedures.To facilitate machining tasks, it is preferred that a part has as many as possible flat or vertical surfaces with respect to the building direction. In the cases of freeform surface designs, an orientation that minimizes the number of undercutnonundercut transitions is most desirable since a surface without being split can be machined in one single operation which eliminates marks resulting from the layer interfaces.An approach that maps surface normals to a unit sphere and determines the orientation that results in the minimum number of undercutnonundercut transitions is described in [Rajagopalan, Pinilla et al. 1998].An algorithm that finds a feasible solution for this deposition is described in [Ramaswami, Yamaguchi et al. 1997]. In short, once a building direction has been determined, this approach identifies all silhouette edges that denote transitions from nonundercut surfaces to undercut features or vise versa. A collection of these silhouette edges together with existing edges form a loop, which is used to split the surfaces. Models are then deposed and support structures are generated with the help of several extrusion operations. Although this approach gives a solution of deposition, the following issues need to be addressed to achieve a better solution:Parts may be deposed to several smaller features or may result in sharp cavities that do not exist in the original design. These features increase difficulty in machining and may require more expensive and timeconsuming processes, ., electrical discharge machining (EDM) for metal a part is deposed into several subvolumes, their shared surfaces need not be defin