Rapid prototyping refers to the automatic construction of mechanical models with 3D printers or stereolithography machines. Rapid prototyping is a type of computer aided manufacturing (CAM) and differs little from rapid manufacturing.
There are two main methods of rapid prototyping, which are derived from similar approaches in sculpture. In additive prototyping, the machine reads in data from a CAD drawing, and lays down successive millimeter-thick layers of liquid plastic or some other building material, and in this way builds up the model from a long series of cross sections.
The subtractive method is earlier and less efficient. In this technique the machine starts out with a block of plastic and uses a delicate cutting tool to carve away material, layer by layer to match the digital object. This is similar to a computer controlled lathe, and is not usually considered a rapid prototyping machine any more.
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 what is left is a functional plastic machine. 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.
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.
Rapid prototyping also describes a software development methodology.