In the additive RP processes, photopolymer systems are based on suc- cessively depositing thin layers of a liquid resin, which are then solidi- fied by exposure to a specific wavelengths of light. Thermoplastic sys- tems are based on procedures for successively melting and fusing solid filaments or beads of wax or plastic in layers, which harden in the air to form the finished object. Some systems form layers by applying adhe- sives or binders to materials such as paper, plastic powder, or coated ceramic beads to bond them. The first commercial RP process introduced was stereolithography in 1987, followed by a succession of others. Most of the commercial RP processes.
