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发表于 2013-10-31 22:26:01
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Rapid Prototyping
The introduction of solid modeling made possible a new industry called Rapid Prototyping (RP), Additive Manufacture (AM), Solid Freeform Fabrication (SFF), or Additive Fabrication (AF). Rapid prototyping refers to the creation of physical models directly from an electronic part file using an additive process. That is, the model is created by building it layer by layer rather than starting with a block and then removing material to create the finished shape.
The first commercial RP method to be introduced was stereo lithography in 1987. In brief, this process, a photopolymer, a liquid resin that cures under the application of certain wavelengths of light, is cured layer by layer by a precisely guided laser beam.
In the early 1990’s, many new RP processes were commercialized. Among the most important was Selective Laser Sintering (SLS). In this process, plastic powder is sintered, or fused together, by the heat from a precisely guided laser beam.
Another process that achieved commercial success was Fused Deposition Modeling (FDM). The FDM process can be thought of as precisely directing a fine hot glue-gun to build up a part. The thermoplastic is usually ABS which is fed from a spool.
When RP was introduced, the available materials had low strength and were extremely brittle. As a result, the only practical application of RP was to produce visual aids. This use was important, since the effective communication of complex designs can minimize errors in their interpretation.
One of main concerns in the application of RP is the overwhelming cost that is attached to it. The systems that have been mentioned above can easily touch the £70’000 mark and then go onto reach £450’000. When the cost of maintenance, materials and an operator are added even a small model can be a couple of hundred pounds.
Also even though it has Rapid in the title, it can still take a couple of hours for the finished model to materialize, there is no means possible to make a fully functioned model within the hour, if it is to be of a high quality and good finish.
Most RP machines accept as an input a file called a stereo lithography (.sty) file. The structure of a .sty file is simple. The surfaces of the solid model are broken down into triangles, the simplest planar area. Each triangle is defined by four parameters: the coordinates of each of the three corners, and a normal vector that points away from the part, identifying which of the two faces of the triangle represents the outer surface of the part.
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