Beyond the STL File

The STL definition was created by 3D Systems right at the beginning of the development history of AM technology and has served the industry well. There are, however, other ways in which files can be defined for the creation of a slice. Furthermore, the fact that the STL file only represents surface geometry may cause problems for parts requiring certain heterogeneous content. Some of the issues surrounding this area will be discussed in this section.

Direct Slicing of the CAD Model

Since generation of STL files can be time-consuming and error-prone, there may be some advantage from using inbuilt CAD tools to directly generate slice data for AM machines. For most 3D solid modeling CAD systems, it is a trivial task to calculate the intersection of a plane with a model, thus extracting a slice.

This slice data would normally have to be processed to suit the AM drive system, but this can be handled in most CAD systems using macros. Support structures can be generated using standard geometry specifications and projected to the part from a virtual interpretation of the AM machine build platform. Although this approach has never been a popular method for generating sliced data, it has been studied as a research subject and even produced to suit a commercialized variant of the Stereolithography process by a German company called Fockle & Schwarz.

The main barrier to using this approach is that each CAD system must include a suite of different direct cutting algorithms for a variety of machines or technologies. This would be a cumbersome approach that may require periodic technology updates as new machines become available. There may be some future benefits in creating an integrated design and manufacturing solution, especially for niche applications or low-cost solutions. At present, however, it is more prudent to distinguish the creation of design tools from that of AM technology by using the STL format.

Color Models

Currently, many AM technologies are available in the market that can produce color variance components, including full color production, including 3D Systems color binder jetting technology, 3D Systems and Stratasys material jetting machines, and Mcor Technologies sheet lamination systems. Colored parts have proven to be very popular, and other color AM machines are likely to make their way to the market. The traditional STL file does not contain any details pertaining to the color of the component or any of its features. Coloring of STL files is possible and there are currently color definitions of STL files available, but you will be constrained by the fact that a single triangle can only be one particular color. It is therefore much easier to use the VRML painting options that allow you to allocate bitmap images to various facets. In this way, you can take advantage of the color options that the AM machine can give you.

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