Introduction to Rapid Prototyping
|
Rapid Prototyping is a relatively recent technology that allows for the creation of 3 dimensional complex prototypes in very short times. This therefore allows the product design cycle to be greatly reduced, and allows for ideas and concepts to be tested, both from an aesthetic and from a mechanical point of view, at relatively low costs.
Please note that this page is only a brief introduction to Rapid Prototyping. For more complete information, please follow some of the links provided at the bottom of this page.
The basic concept of how rapid prototyping works is relatively simple.
Imagine if you wanted to make a prototype of the head shown on the right. With the older conventional prototyping methods, you would have created a 3 dimensional model in a CAD (Computer Aided Design) program such as SolidWorks, Pro-Engineer, Inventor, etc. This 3D computer model would then have been used to program a CNC (Computer Numerically Controlled) mill, which would have then machined the head out of a solid block of material.
Both the programming time and the machining time are large, and the older CNC method is therefore more expensive and slower than rapid prototyping. The times required for machining complex components can often range from days to weeks.
|
|
Rapid Prototyping, on the other hand, takes a different approach to creating solid models.
The first step is to create a 3D model of your part using your favorite CAD program.
The next step is then taken care of by the Rapid Prototyping machine's software package which takes your model and slices it up into thin slices. The slice thickness can generally be chosen, depending on the machine, to be from around 0.1mm to 0.5mm per slice, and this determines the resolution (quality/ surface finish) of you model. If, for example, you had a model that was 1cm thick and you wanted the finest resolution of 0.1mm then the software would cut your model up into 100 separate slices.
|
The final step in the process is then for the Rapid Prototyping machine to build your model by creating one thin slice of the model, and then creating the following slice on top of the previous one over and over until the entire model is built
The entire build time for a rapid prototype can range from minutes to a day, or so, depending on its size and complexity.
There are a variety of different processes used to build these slices, and each different methods uses different materials and has different advantages. Some of the most commonly used Rapid Prototyping methods are described below.
|
| Method | Surface finish and materials |
| SLA, Stereolithography |
| Stereolithography builds objects a layer at a time by tracing a UV beam on the surface of a vat of liquid photopolymer. This class of materials, originally developed for the printing and packaging industries, quickly solidifies wherever the UV beam strikes the surface of the liquid. Once one layer is completely traced, it's lowered a small distance into the vat and a second layer is traced right on top of the first. The self-adhesive property of the material causes the layers to bond to one another and eventually form a complete, three-dimensional object after many such layers are formed.
This method can produce parts for both aesthetic and functional testing and can produce parts with good snap-fit qualities. |
Stereolithography generally is considered to provide the greatest accuracy and best surface finish of any rapid prototyping technology. Over the years, a wide range of materials with properties mimicking those of several engineering thermoplastics have been developed. Limited selectively color changing materials for biomedical and other applications are available, and ceramic materials are currently being developed. The technology is also notable for the large object sizes that are possible.
On the negative side, working with liquid materials can be messy and parts often require a post-curing operation in a separate oven-like apparatus for complete cure and stability.
|
| SLS, Selective Laser Sintering |
| This method uses a powder which is spread in a layer of the desired thickness, and a laser beam is then passed over the profile of the model slice which cures the powder into a solid in that section. The tray is then dropped down one level, and the next layer of powder is spread and the process repeated for the next slice. |
This method results in a good surface finish and excellent dimensional stability, though not quite as fine as SLA. It can produce parts for both aesthetic and functional testing and can produce parts with good snap-fit qualities. The main advantage of this method is the variety of materials that are available. The most common material used has properties similar to that of glass filled nylon, but other materials include flexible rubber materials, and even steel powders, which can be used to produce tool inserts.
|
| FDM, Fused Deposition Modeling, This is one of the machines AUT has. |
| This method extrudes plastic through a nozzle and builds each section by essentially drawing the shape with the nozzle whilst extruding beads of plastic for that layer. The plastic hardens immediately after being squirted from the nozzle and bonds to the layer below |
This method results in a reasonable surface finish and reasonable dimensional stability. The final part has properties similar to that of ABS plastic. Other materials available for this process include wax for investment casting models
|
| LOM, Laminated Object Manufacturing |
| This is one of the older methods and simply cuts each layers profile out of a sheet of paper or plastic and bonds each sheet to the previous one. |
This method results in a reasonable surface finish and reasonable dimensional stability. The finish is similar to that of wood, and the part can then be worked on as if it were wooden This method is still often used to produce patterns for sand-casting.
|
| 3D Printing, This is one of the machines AUT has. |
| This method is one of the more recent ones and uses standard inkjet technology to print each slice of the model, one layer on top of the other until the model is built |
This method results in a reasonable surface finish and reasonable dimensional stability. The most commonly used materials are starch or plaster, so the models are not all that strong. They can however be further strengthened by infusing them with wax or epoxy. Newer models of the printers can now print in color, using different colored materials, and printing logos, etc. as the model is being built.
|
|
Once a rapid prototype has been made, it can then be used to produce metal components should they be required. The most common method for producing metal parts is Lost Wax Investment Casting. This process most commonly uses the rapid prototype to make a silicone mold. This mold can then be used to produce wax models of the component which are then coated in a ceramic slurry. Once hardened, the ceramic and wax model is fired which cures the ceramic and melts away the wax, which then leaves a ceramic mold into which metal (aluminum, bronze, gold, etc.) can be cast. Once the metal has hardened, the ceramic mold can be broken away leaving the final metal component. This lost wax process is also commonly used by jewelers and artists to produce their wares. |
This page only gives a very high level, and possibly simplistic, view of the rapid prototyping process. For more complete information please follow some of the links below:
|
Further Reading and Links
The rapid prototyping Home page: www.cc.utah.edu/~asn8200/rapid.html
Castle Island's Worldwide Guide to Rapid Prototyping: home.att.net/~castleisland
|
