= Feed a device with blueprints for a solid object of your choosing, then let the machine build it for you from plastic or other simple materials 
Video illustration at http://www.youtube.com/watch?v=6FTxd9wwwyg
"3D Printing” is an umbrella term that covers four distinct manufacturing technologies. All are “Additive Fabrication” processes that create objects by adding material in thin layers until a product is completed. Each technology addresses the challege differently with accompanying benefits and drawbacks." (http://replicatorinc.com/blog/2009/02/4-types-of-3d-printing/)
"Three-dimensional printers, often called rapid prototypers, assemble objects out of an array of specks of material, just as traditional printers create images out of dots of ink or toner. They build models in a stack of very thin layers, each created by a liquid or powdered plastic that can be hardened in small spots by precisely applied heat, light or chemicals." (http://www.nytimes.com/2007/05/07/technology/07copy.html?)
"3D Printing is a technique that deposites material layer by layer using a head similar to that of a inkjet printer. The head tends to move along the X and Y axes and the object being printed moves up and down on the Z axis." (http://www.shapeways.com/blog/archives/39-3D-Printing.-A-definition-and-links.html)
Discussing the Definition
"3D Printing is currently rather a hard term to define. Officially it is just one of the rapid manufacturing techniques. Currently however the term 3D Printing itself is used as a synonym for Rapid Manufacturing, Digital Manufacturing, Direct Digital Manufacturing, Rapid Prototyping, Desktop Manufacturing, Freeform Fabrication, Electron Beam Freeform Fabrication and Fabbing.
Each one of these terms has a distinct meaning but they are all vying for your attention to become the official term to describe any process whereby the information in a digital file describing an object virtually(such as an STL or CAD file) is used to rapidly make a real object. Usually by one single machine and usually in limited production runs.
The official definition maintains that 3D Printing is is just one of the many ways that you do this. In that light: 3D Printing is a technique that deposites material layer by layer using a head similar to that of a inkjet printer. The head tends to move along the X and Y axes and the object being printed moves up and down on the Z axis. In the picture above you can see our Objet printer at work. The head is printing two copies of Macouno's Shapeways model Petunia(Of Project Petunia fame). The two Petunias are on a base plate that moves down along the Z axis to give the model depth.
At Shapeways we have noticed that we, our designers and partners tend to use 3D Printing as a general term to describe any rapid manufacturing technique." (http://www.shapeways.com/blog/archives/39-3D-Printing.-A-definition-and-links.html)
"The three leading 3-D printer companies all used different technologies. Stratasys makes models out of liquid plastic using a very expensive heated print head that resembles a glue gun. 3D Systems uses lasers to harden liquid polymers. And the Z Corporation, a unit of the private equity group EQT, builds models by squirting a sort of glue over layers of sandlike plaster." (http://www.nytimes.com/2007/05/07/technology/07copy.html?)
From the Wikipedia:
"One variation of 3D printing consists of an inkjet printing system. Layers of a fine powder (plaster, corn starch, or resins) are selectively bonded by "printing" an adhesive from the inkjet printhead in the shape of each cross-section as determined by a CAD file. This technology is the only one that allows for the printing of full color prototypes. It is also recognized as the fastest method.
Alternately, these machines feed liquids, such as photopolymer, through an inkjet-type printhead to form each layer of the model. These Photopolymer Phase machines use an ultraviolet (UV) flood lamp mounted in the print head to cure each layer as it is deposited.
Fused deposition modeling (FDM), a technology also used in traditional rapid prototyping, uses a nozzle to deposit molten polymer onto a support structure, layer by layer.
Another approach is selective fusing of print media in a granular bed. In this variation, the unfused media serves to support overhangs and thin walls in the part being produced, reducing the need for auxiliary temporary supports for the workpiece.
Finally, ultrasmall features may be made by the 3D microfabrication technique of 2-photon photopolymerization. In this approach, the desired 3D object is traced out in a block of gel by a focused laser. The gel is cured to a solid only in the places where the laser was focused, due to the nonlinear nature of photoexcitation, and then the remaining gel is washed away. Feature sizes of under 100 nm are easily produced, as well as complex structures such as moving and interlocked parts.
Each technology has its advantages and drawbacks, and consequently some companies offer a choice between powder and polymer as the material from which the object emerges. Generally, the main considerations are speed, cost of the printed prototype, cost of the 3D printer, choice of materials, color capabilities, etc." (http://en.wikipedia.org/wiki/3D_printing)
From the Replicator blog :
3D Printing Proper
"usually refers to object made using ink jet technology in three dimensions. As it’s name implies it is a close cousin to traditional 2D printing. These printers work by layering powder a powder substrate and binding it with pigmented glue"
The major manufacturer of 3D printing equipment is ZCorp.
"creates models by heating and extruding a filament of plastic material. Fused Deposition Modeling (FDM) creates models by heating and extruding a filament of plastic material. Stratasys commercialized this technology and owns the trademark.
"produces models by tracing a beam of UV light over a photosensitive pool of liquid. Over time the part is lowered into the bath and the final product is produced. The major benefit of this 3D printing technology is the high level of detail and surface finish it enables."
The Viper line of stereolithography apparatuses (SLA’s) manufactured by 3D Systems produce the highest quality 3D prints available.
"the awesome union of 3D printing and Lasers. The process is similar to stereolithography replacing the UV light with a laser and a vat of liquid with a powdered base. The major benefit of SLS is the ability to produce parts in a variety of materials ranging from plastics to ceraminc to metals."
The Sinterstation by 3D Systems is an example of this technology in practice.
"In addition, two other 3D printing technologies are maturing, but neither is in wide use yet.
Laminated Object Manufacturing (LOM) machines cut and glue thousands of sheets of material together to form solids. MCOR Technology has released a new 3D printer that promises to drastically reduce the cost of 3D printing by using standard A4 paper as the build material.
Electron Beam Melting (EBM) is similar to SLS technology except the process is far more exacting and capable of producing implant grade parts to be used in orthopedic surgery. The final product is higher quality and better embodies the traditional material characteristics making it a true replacement for standard manufacturing techniques. Arcam is the leading the charge in this exciting field." (http://replicatorinc.com/blog/2009/02/4-types-of-3d-printing/)
"Colleges and high schools are buying them for design classes. Dental labs are using them to shape crowns and bridges. Doctors print models from CT scans to help plan complex surgery. Architects are printing three-dimensional models of their designs. And the Army Corps of Engineers used the technology to build a topographical map of New Orleans to help plan reconstruction.
Entrepreneurs like Fabjectory are beginning to find interest in 3-D printing among aficionados of online games, like Second Life and World of Warcraft, in which players design their own characters. Electronic Arts hopes to offer a similar service to create three-dimensional models of characters in Spore, a game to be introduced later this year." (http://www.nytimes.com/2007/05/07/technology/07copy.html?)
2. 3D Printing as a Shopping Service:
"This is a newly emerging mode, where the price of equipment and media are low enough to support a burgeoning industry of service bureaus.
These services accept or provide 3D models that can remotely print objects that are then physically transported to the recipient.
The service is used when the client is unable to afford their own equipment, and will be popular with anybody who needs occasional 3D printing." (http://ecommerce.typepad.com/exciting_ecommerce/2008/02/3d-printing-als.html)
Cathy Lewis, August 2008, on the commercial situation:
"The current vendors like Stratasys, ZCorp, Objet and 3d Systems are not household names as you see in the 2d printing space.
In fact, few outside the industry have ever heard of them and after almost 20 years they continue to be relatively small companies with revenues ranging from $50M to $150M dollars annually. And most of them, with one exception, are very profitable and growing rapidly." (http://ecommerce.typepad.com/exciting_ecommerce/2008/07/3d-printing-des.html)
Projects and Companies
- See also: Desktop Manufacturing; Rapid Manufacturing; Personal Fabricators
- Online tutorial through slideshow: Five Ways to Print Your Own 3-D Objects
- Three videos on 3d printing collected by The Scientific Indian, at http://scienceblogs.com/thescian/2008/08/3d_printing.php
- Four types of 3d-printing: with videos for each