Collective term for modern generative techniques used for incremental manufacture of objects from amorphous raw materials (powders, liquids) or standardised shapes (e.g. milling blocks) using computer-controlled design and manufacture (CAD-CAM) based on three-dimensional datasets (e.g. in STL format).
Originally they were mainly used according to the name for cost-effective fabrication of prototypes and small batch production for testing before completion and/or mass production. Using follow-up techniques (e.g. impression or casting) lost-wax or permanent moulds can be produced in which workpieces are fabricated from other materials.
There is a (decreasing) difference to rapid manufacturing, which is mainly used for the quick production of customised units (e.g. for customised dental laboratory restorations).
Rapid prototyping machines (called "digital fabricators" or "fabbers") are becoming increasingly more efficient, inexpensive and precise. They are now affordable for private users. In the professional sector they are also becoming an increasing part of the digital workflow in dentistry and dental technology.
Basically, there is a difference between subtractive techniques in which the workpiece is carved from a block of material using machine tools (e.g. CNC milling), generally involving a high loss of material, and additive techniques ("3-D printing") in which minute material portions (often resin, plastic or metal) are continuously added to fabricate the virtually designed end product physically. It is now possible to process two or more materials and combine them into one workpiece.
Stereolithography and [MJM] multi jet modelling (also poly jet modelling)
Incremental polymerisation of liquids, light-curing monomers using UV or laser exposure. The workpiece is created by lowering the section already fabricated in the resin/plastic material by a defined slice thickness (usually approx. 100 µm). Undercuts can only be produced using support frameworks, either using the same polymer (must be cut out) or using another material, e.g. thermoplastic wax or plastic (can be melted out). The frameworks must be removed after fabrication of the workpiece. The typical accuracy is about 100 µm to 10 µm. In micro stereolithography (also "RMPD" Rapid Micro Product Development), which is used for the manufacture of microchips for example, slice thicknesses and accuracies of up to 1 µm can be achieved; the possible workpiece diameter is, however, limited to a few centimetres.
Laser sintering, (also selective laser sintering, SLS)
Materials in powder form (plastic, metal or ceramic) are melted/ fused by exposure to a laser beam and gradually built up in thin slices to a solid workpiece. Undercuts are possible, no support framework is required. Rapid Tooling, which is used for the fabrication of metal shapes and tools for processing plastics for small and medium batches/ quantities, is also possible using metal laser sintering.
The following variations of the procedure are differentiated thus:
- Material particles are only partially melted and "baked" together (metals with binders/ sintering additives and plastics).
- Powder particles are completely melted (selective laser melting, SLM) and fuse into one another (metals without binding agents).
- Using laser micro-sintering, e.g. ceramic nanoparticles (diameters of about one µm) can be formed into microworkpieces.