3D printing is used to come up with three dimensional objects and is a form of additive manufacturing. It is now easier and more affordable to come up with a prototype using the 3D technology. Before these technologies were introduced, it used to take several hours, skilled labor and tools to create a prototype.
One form of 3D printing technology is made up of inkjet printing systems. Fine powder layers made of resins, corn starch or plaster is bonded selectively on adhesives produced by the inkjet print heads. This kind of technology makes it possible to print a full color prototype and is considered to be one of the fastest methods.
Another technology involves the use of machines that feed liquids like photopolymer using an inkjet print head to create every layer of the model. This kind of photopolymer machine uses an ultraviolet flood lamp that is placed on the print head so that each layer is cured once it is deposited.
Fused deposition modeling is also used as a 3D technology and is mainly applied is traditional prototyping. This technology makes use of nozzles to place the molten polymer on a support structure. The molten polymer has to be deposited layer by layer.
Selective fusing is also a 3D printing technology that involves the use of printing media on a granular bed. In this type of technology, the media that is not fused is used to provide support for overhangs and thin walls in the areas that are being produced. This reduces the need to use auxiliary supports to hold the workpiece. A laser is used for sintering the media to create a solid.
Some companies use 3D micro fabrication which involves tracing the 3D object that you want to create on a gel block using a focused laser. The gel will only become solid on the parts where the laser is focused. [Source]