How CAD STL Files Are Used in Rapid Prototyping

In rapid prototyping, the process begins by creating a three-dimensional CAD model of the part according to the drawing or design intent. This model is usually designed in 3D CAD software and then exported in STL format, which is the most commonly supported file type in rapid prototyping systems.

The STL model represents the surface of a solid part by approximating it with a large number of small flat triangular facets. In other words, the original curved or complex surface of the CAD model is converted into a mesh made of planar triangles. This surface approximation method simplifies the data structure of the model and makes it easier to process in later slicing and layer manufacturing steps.

Because STL data is relatively simple to process and largely independent of the original CAD system, it quickly became the standard data exchange format between CAD software and rapid prototyping machines. In an STL file, each triangular facet is typically defined by four sets of data: the coordinates of three vertices and one normal vector. The entire CAD model is therefore represented as a collection of these triangular surface elements.

In most CAD software systems, the output accuracy of the STL model can be adjusted to reduce surface approximation error. By selecting suitable export parameters, the user can improve the quality of the STL file and reduce the deviation between the original CAD surface and the triangulated model. This is important because STL accuracy directly affects slicing quality, surface finish, and the dimensional precision of the final rapid prototyping part.