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 cast ing.

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.

Contents

1 Stereolithography 2 Fused Deposition Modeling 3 Inkjets 4 Selective Layer Sintering 5 External links

Stereolithography

Currently the most widely used technology, Stereolithography is considered to provide the greatest accuracy and best 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

A plastic filament 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 plastic 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

There are two Inkjet methods - Thermal Phase Change Inkjets and Photopolymer Phase Change Inkjets. 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 aftern being deposited due to a rapid drop in temperature. Once a single layer has been deposited, a milling head may be empolyed to ensure uniform thickness before the next later is deposited. The technique is typically very slow, but can obtain high resolution, often comparibe to a CNC milling machine. The materials employed result in fragile parts. Photopolymer Phase machines employ an Ultraviolet (UV) flood lamp mounted in the print head to cure each later as it is deposited.

Selective Layer Sintering

In this method, a laser selectively fuses powdered material. Then the part is lowered and a new layer of material is rolled on.

External links

• eMachineShop - machine shop where parts designed in CAD software can be ordered online, automatically manufactured and delivered.