Rapid manufacturing:
See also: Rapid Prototyping
Rapid manufacturing is a technique for manufacturing solid objects by the sequential delivery of energy and/or material to specified points in space to produce that solid. Current practice is to control the manufacturing process by computer using a mathematical model created with the aid of a computer. Rapid manufacturing provides a large advantage in speed and cost overhead compared to alternative metal manufacturing techniques such as powder metallurgy manufacturing or die casting.
Variously called rapid prototyping, freeform fabrication (FFF), solid freeform fabrication (SFF), layered manufacturing and 3D printing. Encompasing techniques such as stereolithography (SLA for stereolithography apparatus), selective laser sintering (SLS), fused deposition modeling (FDM), laminated object manufacturing (LOM), inkjet systems and three dimensional printing (3DP). Unlike methods such as CNC milling, these techniques allow the fabricated parts to be of high geometric complexity.
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Stereolithography (SLA)
One of the more commonly used rapid manufacturing techologies, Stereolithography is considered to provide high accuracy and good surface finish. It involves building plastic parts a layer at a time by tracing a laser beam on the surface of a vat of liquid photo-polymer. The photopolymer is solidified by the laser light. Once one layer is completely traced, it is lowered a small distance into the liquid and a subsequent layer is traced, adhering to the previous layer. After many such layers are traced, a complete 3D model is formed. Some specific technologies require further curing of the polymer in an oven. For models that have delicate structures that must be supported against gravity to prevent collapse, fine supports may be added during fabrication, either automatically in software or manually, and subsequently removed.
Fused Deposition Modeling (FDM)
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. In a similar manner to Stereolithography, the model is built up from layers as the plastic hardens immediately after extrusion from the nozzle. Several materials are available with different trade-offs between strength and temperature. A water-soluble material is available, which can simply be washed away after fabrication.
Inkjets or 3D printing
Similar in concept to Inkjet printers used for printing ink on paper, these machines feed liquids into individual jetting heads which squirt tiny droplets as they are scanned to form a layer of the model. The liquid hardens after being deposited. Once a single layer has been deposited, a milling head may be employed to ensure uniform thickness before the next later is deposited. The technique is typically very slow, but can obtain high resolution, often comparable to a CNC milling machine. The materials employed result in fragile parts. Materials available for spraying include glue, wax, starch, and photopolymer. Photopolymer Phase machines employ an Ultraviolet (UV) flood lamp mounted in the print head to cure each later as it is deposited.
Selective Laser Sintering (SLS)
In this method, a laser selectively fuses powdered material (e.g, metal or glass). Then the part is lowered and a new layer of material is rolled on. Parts are typically porous and can be dipped in another liquid with a lower melting point to create a more solid part.
Laser Engineered Net Shaping (LENS)
A laser is used to melt metal powder and deposit it on the part directly. This has the advantage that the part is fully solid (unlike SLS) and the metal alloy composition can be dynamically changed over the volume of the part.
Laminated Object Manufacturing (LOM)
Sheets of paper or plastic film are attached to previous layers by either sprayed glue, heating, or embedded adhesive, and then the desired outline of the layer is cut by laser or knife. Finished product typically looks and acts like wood.
Microfabrication or lithography process
A material (like silicon wafers) is repeatedly photoetched and recoated to form a part in layers.