Rapid Prototyping

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  • Topic: Rapid prototyping, Selective laser sintering, Stereolithography
  • Pages : 17 (4620 words )
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  • Published : April 16, 2013
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Introduction|
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Rapid Prototyping (RP) can be defined as a group of techniques used to quickly fabricate a scale model of a part or assembly using three-dimensional computer aided design (CAD) data. What is commonly considered to be the first RP technique, Stereolithography, was developed by 3D Systems of Valencia, CA, USA. The company was founded in 1986, and since then, a number of different RP techniques have become available.Rapid Prototyping has also been referred to as solid free-form manufacturing, computer automated manufacturing, and layered manufacturing. RP has obvious use as a vehicle for visualization. In addition, RP models can be used for testing, such as when an airfoil shape is put into a wind tunnel. RP models can be used to create male models for tooling, such as silicone rubber molds and investment casts. In some cases, the RP part can be the final part, but typically the RP material is not strong or accurate enough. When the RP material is suitable, highly convoluted shapes (including parts nested within parts) can be produced because of the nature of RP.There is a multitude of experimental RP methodologies either in development or used by small groups of individuals. This section will focus on RP techniques that are currently commercially available, including Stereolithography (SLA), Selective Laser Sintering (SLS®), Laminated Object Manufacturing (LOM™), Fused Deposition Modeling (FDM), Solid Ground Curing (SGC), and Ink Jet printing techniques.|

Highlights of Stereolithography|
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  •| The first Rapid Prototyping technique and still the most widely used.| •| Inexpensive compared to other techniques.|
| Uses a light-sensitive liquid polymer.|
| Requires post-curing since laser is not of high enough power to completely cure.| •| Long-term curing can lead to warping.|
| Parts are quite brittle and have a tacky surface.|
| No milling step so accuracy in z can suffer.|
| Support structures are typically required.|
| Process is simple: There are no milling or masking steps required.| •| Uncured material can be toxic. Ventilation is a must.|
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Introduction to Stereolithography|
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Stereolithography (SLA), the first Rapid Prototyping process, was developed by 3D Systems of Valencia, California, USA, founded in 1986. A vat of photosensitive resin contains a vertically-moving platform. The part under construction is supported by the platform that moves downward by a layer thickness (typically about 0.1 mm / 0.004 inches) for each layer. A laser beam traces out the shape of each layer and hardens the photosensitive resin. The Stereolithography (SLA) System overall arrangement: |

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Stereolithography Process|
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The sequence of steps for producing an Stereolithography (SLA) layer is shown in the following figures: Uncured resin is removed and the model is post-cured to fully cure the resin. Because of the layered process, the model has a surface composed of stair steps. Sanding can remove the stair steps for a cosmetic finish. Model build orientation is important for stair stepping and build time. In general, orienting the long axis of the model vertically takes longer but has minimal stair steps. Orienting the long axis horizontally shortens build time but magnifies the stair steps. For aesthetic purposes, the model can be primed and painted. During fabrication, if extremities of the part become too weak, it may be necessary to use supports to prop up the model. The supports can be generated by the program that creates the slices, and the supports are only used for fabrication. The following three figures show why supports are necessary: |

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Highlights of Selective Laser Sintering|
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  •| Patented in 1989.|
| Considerably stronger than SLA; sometimes structurally functional parts are possible.| •| Laser beam selectively fuses powder materials: nylon, elastomer, and soon metal;|...
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