Three-Dimensional Printing

Probably the fastest of all rapid prototyping methods, Three-Dimensional Printing offers the advantages of speedy fabrication and low materials cost. As shown in the following illustration, in Three-Dimensional Printing, a liquid adhesive compound is deposited onto the top layer of a bed of powder object material (B) by a multi-channel ink jetting head (A). The particles of the powder become bonded in the areas where the adhesive is deposited and once a layer is completed, a piston (C) moves down by the thickness of a layer. A similar piston within the powder supply system (E) moves upward incrementally to supply powder for the process, and a roller (D) spreads and compresses the powder on the top of the build cylinder, until the entire object is completed within the powder bed. After completion the object is elevated and the extra powder brushed away, leaving a "green" object.

Stereolithography

Stereolithography on the other hand, the most widely used rapid prototyping technology, builds plastic parts or objects a layer at a time by tracing a laser beam on the surface of a vat of liquid photopolymer. This class of materials, originally developed for the printing and packaging industries, quickly solidifies wherever the laser beam strikes the surface of the liquid. Once one layer is completely traced, it's lowered a small distance into the vat and a second layer is traced right on top of the first. The self-adhesive property of the material causes the layers to bond to one another and eventually form a complete, three-dimensional object after many such layers are formed. Upon completion of the fabrication process, the object is elevated from the vat and the supports are cut off.

Stereolithography generally is considered to provide the greatest accuracy and best surface finish of any rapid prototyping technology.  Over the years, a wide range of materials with properties mimicking those of several engineering thermoplastics have been developed. The technology is especially notable for the large object sizes that are possible.