Introduction to Rapid Prototyping
In research, development and study, prototypes play an important role. These developed prototypes help to do testing prior to production and help to pinpoint the possible problems that are occurring due to the design faults. Earlier generating a prototype model was extremely costly process and also time taking. But with the aid of Computer Numerically Controlled (CNC) Machining, the speed at which a prototype is developed has increased. With Rapid Prototyping, this time period has even decreased from few days to a few hours.

Rapid Prototyping is an additive manufacturing process that generates a model of an object directly from a CAD model by building it in layers. For this computerized equipment are used that builds a three-dimensional model of a casting from a CAD drawing.

There are different forms of Rapid Prototyping available depending upon the needs. One can differentiate between them by the methods these systems employ to make the layers. Following are few of the main types of Rapid Prototyping:

Stereolithography (SLA)
Stereolithography uses UV ray to solidify liquid acrylic polymer layer by layer on a moving platform and after many layers, the prototype in the preferred form is formed. This process is carried on in a VAT, a device that is filling up with photocurable liquid acrylate polymer. Stereolithography is one of the most used forms of rapid prototyping because of accuracy (Tolerances= 0.0125mm), less time taken (depends upon the size and complication of the part) and where parts details are fine and their geometry is to difficult to machined.

Fused Deposition Modeling (FDM)
Fused deposition modeling also referred as FDM, is a rapid prototype technology commonly used to convert CAD drawings into physical parts. FDM is a trademark of Stratasys and was developed by S. Scott Crump.

FDM works on an “additive” principle which extrudes material in layers. Plastic or wax is melted and liquefied in the extrusion head and extruded through a nozzle. The nozzle is made to move over a trail identified by the CAD design to produce part. This way single layer is extruded and then it is dropped to extrude the next layer on top of the first until the entire prototype is built, with one layer at a time.

Selective Laser Sintering (SLS)
Selective Laser Sintering uses the principle of sintering. Sintering is a heating process that prevents melting and a coherent mass is produce. In SLS, metallic or non-metallic powders are sintered using a CAD program guided laser that selectively fuses the powdered material.

There are few more types of Rapid Prototyping available, like; Laminated Object Manufacturing, 3D Printing, Solid Base Curing, Optical Fabrication and Photochemical Machining.

Rapid prototyping has provided designers with several benefits. Designers can look their parts and in case any error occurs they can easily fix it. Apart from industrial use they have formed part of manufacture. This development process provides blank patters for use in casting. RP has also proliferated biomedical science.

About The Author

Jon T Smith

For those involved in product development, engineering, and other form-giving applications, rapid prototyping (RP) technology can offer an excellent deliverable for various applications. Prototyping can be used for concept generation, ergonomic testing, test fitting, functional testing and even small-batch production.

There are various rapid prototyping technologies available for use including Fused Deposition Modeling (FDM), Stereolithography (STL), Selective Laser Sintering (SLS), and 3D Printing. Each of these technologies has advantages and disadvantages.

Fused Deposition Modeling technology is marketed commercially by Stratasys, which also holds a trademark on the term. Like most other RP processes FDM works on an “additive” principle by laying down material in layers. A plastic filament or metal wire is unwound from a coil and supplies material to an extrusion nozzle which can turn on and off the flow. The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism, directly controlled by a computer-aided design software package. In a similar manner to stereolithography, the model is built up from layers as the material hardens immediately after extrusion from the nozzle.

Stereolithography is an additive fabrication process utilizing a vat of liquid UV-curable photopolymer “resin” and a UV laser to build parts a layer at a time. On each layer, the laser beam traces a part cross-section pattern on the surface of the liquid resin. Exposure to the UV laser light cures, or, solidifies the pattern traced on the resin and adheres it to the layer below.

Selective laser sintering is an additive rapid manufacturing technique that uses a high power laser to fuse small particles of plastic, metal, ceramic, or glass powders into a mass representing a desired 3D object. The laser selectively fuses powdered material by scanning cross-sections generated from a 3D digital description of the part on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed.

3D printing is a unique form of prototype creation that is rooted in traditional rapid printing technology. A three dimensional object is created by layering and connecting successive cross sections of material. 3D printers are generally faster, more affordable and easier to use than other additive fabrication technologies. While prototyping dominates current uses, 3D printing offers tremendous potential for retail consumer uses, especially because the cost of production is less than other methods, and the part build time is minimal. In the latest incarnations, 3D color printing is also available. This means that a part can be printed to represent the colors of the finished product, to show label concepts or requirements, or to indicate the results of stress analysis or other failure mode effects (FME) analysis.

For the most part, all rapid prototype systems require a 3D computer model to start the process. In most cases a significant amount of file preparation must be undertaken to get a file to generate a correct rapid prototype model.

As part of the innovation process, some companies may employ one or several rapid prototyping technologies in-house. However, being a new “cutting-edge” technology, many firms can make use of service bureaus to provide their rapid prototyping as the need becomes evident. Most service bureaus have detailed websites to market and serve their customers.

A handful of service bureaus are fairly large companies with numerous employees and locations. Many provide related services and technologies, such as tooling, industrial design, molding and production. However, service bureaus are typically small companies, and while they may be small, many of them are vertically integrated and can provide services from concept models to finished functional parts.

Service bureaus tend to specialize in one or more areas such injection molding, casting, etc. Examine a company’s portfolio or case histories on their web pages, or discuss previous projects with the company to try to better understand areas of particular expertise. Sculptors have also used the technology to produce complex shapes for fine arts exhibitions.

In the near future, rapid prototype technology will become more widespread and pervade even to the home. For now though, for timely and expert delivery, the use of a service bureau is the best way for most innovative companies, individuals and organizations.

About The Author

Geoffrey Brennan