What is Rapid Prototyping?
Rapid prototyping, automatic additive fabrication, solid freeform fabrication, three dimensional printing are several names that denote an automatic manufacturing process for creating physical models or prototypes.
Rapid prototyping is an automatic additive manufacturing process. From CAD (computer aided design) data a model is designed. It must be a solid model but after that, any geometry is applicable. At that point the files are saved as an STL file and are sent to a service bureau. The bureau slices up the cad model into cross sections. Those cross sections are then automatically fabricated one on top of the other until the model is done. There are various processes and materials available. Each has its own interesting advantages and disadvantages. The fabrication has the look and feel of a topological model but with layers that are only .004". It was primarily developed and used in aerospace, automotive, toy and medical applications.
The epiphany that is so basic to rapid prototyping is that anything you can imagine and create in cad can be built. As well, rp is a what-you-see-is-what-you-get process. What you see in your mind, on your cad screen, can be built in a model. At the same time rapid prototyping has another distinct advantage. It fabricates objects additively. This is a simple yet profound difference. Undercuts, convolutions of form, intricate geometry, all are easily accomplishable in an additive process. This is different from CNC milling which is subtractive and cannot create undercuts and convolutions.