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Rapid Prototyping (RP) allows for fabricating a scale model of a part or assembling a model quickly. Also known as sold form-free manufacturing, computer automated manufacturing or layered manufacturing, it entails automatic construction of physical objects using additive manufacturing technology.
There are different types of rapid prototyping techniques to move your ideas from paper to reality. Different techniques have emerged over the years with improvements in technology. Each new technique, while an improvement over the previous one is not necessarily a replacement, but rather serves a different or wider purpose. As such, there are many RP techniques in use now, and with technology ever-evolving, new techniques become more popular each day.
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Stereo-lithography (SLA), developed by 3D Systems of Valencia California was the earliest Rapid Prototyping (RP) technique, and still remains the most widely used technique owing to its simplistic and inexpensive nature.
SLA requires placing any light-sensitive liquid polymer in a vat of photosensitive resin. A laser beam traces out the shape of each layer and hardens the photosensitive resin to create the desired object. A vertically moving platform inside the vat allows the laser to advance layer by layer, tracing the cross-section of the model.
The biggest advantage of SLA is its simplistic nature, with no milling or masking required. SLA is, however, not without its cons. It requires a complex arrangement of a vat, vertically moving platform, and support structures. Lasers do not have power to cure completely, and as such, this technique requires post-curing. Long-term curing not only consumes time but may cause warping. Moreover, the parts may become brittle and develop a tacky surface, and the accuracy remains suspect.
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Selective Laser Sintering (SLS)
Carl Deckard, a University of Texas student patented the Selective Laser Sintering (SLS) RP technique in 1989. Here, a laser beam fuses the power of many possible materials such as nylon, glass-filled nylon, polycarbonate, elastomer and metal selectively. The use of a sealant avoids the powdery porous surface and adds to the strength.
SLS scores over SLA in its strength and ability to use common engineering plastic materials. Unlike SLA, which is limited to brittle photosensitive resins, SLS may process polymer powders that adds to the strength and does away with warping and brittleness. Moreover, simply brushing or blowing removes the uncured material. The process itself in simple, but the absence of a milling step may cause accuracy to suffer.
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Fused Deposition Modeling (FDM)
Developed by Scott Crump in 1988, Fused Deposition Modeling (FDM) involves heating standard engineering thermoplastic polymers in a tube and squeezing them out like a toothpaste to the desired model. The use of a second material allows for latticework interiors. Maintaining the platform at a lower temperature facilitates rapid cooling.
FDM is fast growing in popularity owing to the ability to shape the material to the desired property with considerable ease. The process scores on flexibility, with several machine options ranging from fast concept modelers to slower, high-precision machines. One major drawback is the absence of the milling step that makes layer deposition non-uniform at times, skewing the plane.
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Electron Beam Melting (EBM)
Developed by Arcam AM of Sweden, the electron beam melting (EBM) technique involves melting metal powder layer by layer using an electron beam that reads data from a 3D CAD model. The process takes place in a high vacuum environment allowing for a dense, void free and robust output. Titanium alloys remain the most popular metal in use for this purpose.
EBM scores on its extremely precise and high quality output but on the flip side, is costly and demands high skill-levels.
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Laminated Object Manufacturing (LOM)
The process of Laminated Object Manufacturing (LOM) involves stacking layers of glue backed paper, plastic or metal laminate. A heat roller adheres the sheets to substrate, and a laser traces the outline of the layer. Cross-hatching removes the material outside the model. The models are then sealed to prevent moisture from seeping in.
The biggest advantage of LOM is the ready availability of raw materials. The absence of any chemical reaction allows making large parts, but again the lack of milling step results in low accuracy.
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Solid Ground Curing (SGC)
Developed by Cubital, Inc. of Israel, Solid Ground Curing (SGC) or the Solider Process Method uses a laser printing process to create masks and then exposes the full layer at once. When using wax as the medium, the model requires no extra support.
This biggest advantage of SGC is the ability to fabricate large parts up to 500 × 500 × 350 mm (20 × 20 × 14 inches) quickly without post-cure concerns. Hardening each layer of photosensitive resin at once increases speed. The presence of a milling step ensures flatness for subsequent layer. However, on the flip side, this technique creates a lot of waste.
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3D Printing uses the same approach as Laminated Object Manufacturing. A power delivery system moved up a set distance deposits layers of material powder in the fabrication chamber, and a roller distributes and compresses the powder evenly. A multi-channel jetting head then works on the powder bed to create a layer of liquid adhesive, which bonds and hardens to create the required form. With one such layer completed, the fabrication piston moves down in increments, depending on layer thickness.
3D printing scores in the speed of executing, low material costs, and the possibility of adding color options. The resolution and surface finish, however, may be suspect, and the product fragile. Steady availability of materials may also pose a serious challenge for manufacturers in some areas.
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There are two common inkjet methods: Thermal Phase Change Inkjet and Photopolymer Phase Change Inkjet
The Thermal Phase Change Inkjet method, also known as Ballistic Particle Manufacturing involves using solid scape machines to hold the build and support materials at elevated temperatures in a reservoir. The liquid material then moves though thermally insulated tubing to individual jetting heads that disperses the material as tiny droplets to the required shape. Layers form as the droplets cool and harden immediately.
The Photopolymer Phase Change Inkjet method utilizes an inkjet head with a wide area. A UV food lamp mounted on the head of the printer exposes completed layers to UV light and hardens the layer. A secondary operation washes away support materials.
Inkjet methods score on finish and speed. The use of multiple jet heads to increase speed, however, compromises accuracy; and the finer the finish desired, more the time required.
The application of different types of rapid prototyping techniques in virtualization, testing, creating male models for tooling, manufacturing production-quality parts in small numbers and other uses allow moving your idea from paper to reality easily. It leads to lesser product development and throughput time, increased product variety, reducing mistakes, minimizing sustaining engineering changes, and allows for the extension of product lifetimes by adding necessary features or eliminating redundant features early in the design phase.
- Image Credit 2: flickr.com/Windell Oskay under CC 2.0 license
- Image Credit 1: geograph.org.uk/John Haynes under Creative Commons license
- UL University: Underwriters Laboratories Inc. “Rapid Prototyping.” http://www.efunda.com/processes/rapid_prototyping/sla.cfm.%20Retrieved%20October%2029, 2011.
- Sarah Westerdale. "Rapid Prototyping." http://www.ferris.edu/cot/accounts/plastics/htdocs/student/Westerdale/Home.htm.%20Retrieved%20October%2029, 2011.