They merely duplicate the external form embedded in external tooling such as dies and molds and the internal form embedded in cores, etc.
This book provides an updated overview of RP technologies at a level of detail that university engineering students taking courses on RP as well R&D and operating professionals from industry interested in RP are likely to find attractive. While the emphasis is on laser-based technologies, other processes are also discussed. With respect to each important RP process, the part/assembly modeling techniques, the materials used, process itself, advantages and disadvantages, accuracy and finish issues as well as application potential are discussed.