Rapid Prototyping, also known by other names such as additive fabrication and solid freeform fabrication is the automatic construction of physical objects using addive processes like selective laser sintering, stereolithography and fused deposition modeling. Today, this technology is used to create a 3-D solid model and sometimes production quality parts in small numbers. Some sculptors also use the technology to produce complex shapes for fine art exhibitions.
Rapid Prototyping takes virtual designs from CAD or an animation modeling software and processes them by transforming them into virtual cross sections, and then forms or manufactures each cross section in physical space, one after the next until the model is finished. It is a 'what you see is what you get' process where the virtual model and the physical model correspond almost identically. The process is similar to the construction of a topographical model where the alternate layers correspond to the elevations.
There are two main methods of rapid prototyping, which are derived from similar approaches in sculpturing. With additive prototyping, the machine reads in data from a CAD file and lays down successive layers of liquid plastic as thin as a micrometer. The machine is adaptable to alternate materials such as powdered plastic or other engineered materials. The primary advantage to additive construction is its ability to create almost any geometry, except of course internal 'negative' geometry or volumes of air. One drawback is that these machines are limited to the size of the parts they can make. Most cannot make parts larger than 4 ft cubed. Monumental parts can be made by automatically carving foam with a hot wire one layer at a time. Several companies have built large scale machines to do this automatically, but most market the product rather than the machine.
The subtractive method is of older technology and is less efficient. In this technique the machine starts out with a block of plastic or wax and uses a delicate cutting tool to carve away material, layer by layer to match the digital object. This is similar to a computer numerical control (CNC) device such as a lathe or a mill. It is similar in concept to a sculptor carving a block of marble or wood where they chip away at the surface of the model until the form of the project begins to emerge. Complex shapes and forms with undercuts are more difficult to accomplish with the subtractive method. Typically these are made in parts and fit together. Subtractive technologies are capable of doing large scale projects.
The standard interface between CAD software and rapid prototyping machines is the .STL format.
Today it is possible to make very high 'resolution' models in layers thinner than 1 micrometer, using UV curing materials that are based on Sol-Gel materials, acrylates, and epoxies.
The word "rapid" is relative: construction of a model with contemporary machines typically takes 3–72 hours, depending on machine type and model size. These machines are used to greatly reduce prototyping time that would be required to machine several parts needed in the prototype. Used in micro technologies "rapid" is correct, the products made are ready very fast and the machines can build the parts in parallel.
Advances in technology allow the machine to use multiple materials in the construction of objects. This is important because it can use one material with a high melting point for the finished product, and another material with a low melting point as filler, to separate individual moving parts within the model. After the model is completed, it is heated to the point where the undesired material melts away, and left is the functional plastic, multi-piece moving part. Although traditional injection molding is still cheaper for manufacturing plastic products, soon rapid prototyping may be used to produce finished goods in a single step.
Other advances may include machines that are both additive and subtractive. Some consider the lamination technologies (laminated object manufacture) to already be dual strategy machines.
Lab tests have shown that prototyping machines can also use conductive metals as a building material, and conceivably in the future could assemble small electronics like mobile phones in a single process. Today its possible to make gems and integrate bare dies at MicroTEC Germany.
Due to the high degree of flexibility and adaptability required by many rapid prototyping techniques, these applications typically require the use of robots or similar mechanisms.
Today, the cheapest rapid prototyping machines cost about 30K, still beyond the reach of most consumers.
However, there are currently several schemes to improve rapid prototyper technology to the stage where a prototyper can manufacture its own component parts. The idea behind this is that a new machine could be assembled relatively cheaply from raw materials by the owner of an existing one. This is a crude form of self replication, but it is a concievable idea in reducing the cost of these machines.
