Virtually all rapid prototyping technologies are presently being used or considered in some form or another for RM. Those that have the advantage of already utilizing target materials in powdered or extruded form predominate at present. The list includes selective laser sintering, Three Dimensional Printing and related technologies.

Those that use photopolymers can be expected to become more important in time. Photopolymers are complex chemical systems requiring substantial development, and only simulate engineering materials rather than directly replace them. However, the liquid state offers the possibility for advantageous and simple handling, and for use with inkjet technology which is highly-adaptable and already finding its way into a broad spectrum of manufacturing processes.

The rapid prototyping technology that is probably the least pertinent to RM is laminated object manufacturing (LOM). The pronounced staircasing of non-vertical surfaces, coupled with the low resolution of the Z-axis resulting from the fixed layer thickness of sheet materials, and the difficulty of removing excess material from inner voids and supports, are features that result in parts that are farther from final requirements than those made by other technologies. However, LOM is not a technology that can be ruled out completely, either. It offers advantages for certain ceramic parts, in the manufacture of composite materials, in making complex fiber-optic structures for communications and in other applications. In addition, there continues to be considerable development work around the world aimed at improving its limitations. LOM provides an example of how no technology can be ruled in or out at present, and of the immaturity of RM in general.

Table 1 gives a representative selection of today's major technologies used to make parts in specific classes of materials. The technologies are arranged roughly top to bottom from most "popular and well-developed" to least. Be forewarned though, that this ranking is incomplete and superficial at this stage.

Table 1. Technologies Being Used for Rapid Manufacturing
Plastic parts selective laser sintering (SLS) Related Processes:      selective mask sintering      [Sintermask GmbH] fused deposition modeling (FDM) stereolithography (SLA) Related Processes:      jetted photopolymers      spatial light modulator-based           exposure technologies	Metal parts selective laser sintering (SLS) Related Processes:      selective laser melting (SLM)      Electron Beam Melting (EBM)           [Arcam AB] laser powder forming Includes:      Optomec LENS (TM)      POM-Group DMD (TM)      others Three-dimensional Printing (3DP) [ProMetal] sprayed metal Includes:      Sprayform [Ford Global Technologies]      Rapid Solidification Process [RSP, Inc.]	Ceramic parts Three-dimensional Printing (3DP) selective laser sintering (SLS) fused deposition modeling (FDM) Robocasting (TM) stereolithography Related Processes:      Optoform (3D Systems)      (now dormant)

There are numerous additional technologies which are being pursued for particular applications or market segments. These range from micro-stereolithography for the manufacture of MEMS and nearly invisible nano-devices to Contour Crafting for the automated manufacture of entire buildings. Some of these processes originated in the RP world, but others were established specifically for additive manufacturing, or arose from rapid tooling roots.

The important point to take away from this discussion is that there are no clear technology winners at present. Each rapid manufacturing application is amenable to a wide array of solutions, and choosing the best approach isn't simple. A multitude of technologies are being tried on an even larger multitude of applications. Rapid manufacturing is still in an era of technological experimentation which can be expected to last several years.