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Rapid Prototypes
Did you know?
The availability of rapid prototypes allows the product and mold designers to view the part in real life without building a mold and molding a prototype. This process allows the part designer an opportunity to check the form, fit and function of a product before releasing the design. The mold designer is also able to work with an actual part and more effectively conceptualize the mold requirements. Acquiring rapid prototypes is very inexpensive and can save valuable time and money in design modifications.
Columbia Plastics Ltd. assists customers routinely in recommending and acquiring SLA model as part of the product development process.
Two of the most common processes for providing 3D rapid prototypes are SLA (Stereolithography Apparatus) and SLS (Selective Laser Sintering) . They can be compared under various features, and characterized by significant highlights as shown in figure 1.
| Accurate |
SLA |
SLS |
Less Accurate |
| Strong |
SLS |
SLA |
Less Strong |
| Fine Resolution |
SLA |
SLS |
Coarse Resolution |
| Smooth Surface |
SLA |
SLS |
Rough Surfacxe |
| Inexpensive |
SLA |
SLS |
Expensive |
| Fast Build |
SLA |
SLS |
Slow Build |
| Excellent for Fit & Form Testing |
Functional Parts, Durable - snap fits & living hinges |
| Standard Tolerance +/-0.005" for the 1st inch, +/-0.002" on every inch thereafter |
Standard Tolerance; +/- 0.005" for the 1st inch, +/- 0.003" on every inch thereafter |
| Good for Visual Aids and Patterns for Tooling |
In Build Up Direction, Standard Tolerance: +/- 0.010" for the 1st inch, +/- 0.003" on every inch thereafter |
| Layer Thickness: 0.002"=0.004" |
Layer Thickness: 0.004" |
| Object Size Typically Larger than SLS |
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Figure 1. Rapid Prototype Process Comparisons |
SLA (Stereolithography Apparatus) process, the most widely used method for rapid prototyping, basically involves building up an object, layer by layer, on a platform which is controlled to move up and down in a container of photo-curable liquid resin. The light of a solid state laser traces the cross sectional slice information of the 3D CAD data onto the surface of a container of liquid photopolymer. Once the layer is completely traced, it is lowered a small distance into the container and a second layer is traced right on top of the first. When completely built up, the three-dimensional object, replicating the 3D CAD data, is removed from the tank, is washed of excess resin and placed in a UV oven for final curing. When cured, the model is finished by smoothing out the stair like transitions between layers.
SLS (Selective Laser Sintering) process uses a laser to sinter powder based materials together, layer by layer, to form a solid model. A thin layer of build material is spread across a platform set in a chamber. A laser traces a two dimensional cross section of the part on the layer, sintering the material together. The platform descends a layer thickness and a levelling roller crosses over the part, applying a fresh layer of material. The next cross section of the part is sintered unto the previous layer. This continues until the complete part is built up. Once complete, the model is removed, any loose material is cleaned off and visible surfaces are smoothed out.
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