STL

STL. It is a file format native to the stereolithography CAD software created by 3D Systems. This format, which has become the *de facto* standard for rapid prototyping and 3D printing, represents the surface geometry of a three-dimensional object using a triangulated mesh. Its simplicity and widespread adoption have made it fundamental to the additive manufacturing industry, despite lacking information about color, texture, or other common CAD model attributes.

Overview

The STL format describes only the surface geometry of a three-dimensional object without any representation of color, texture, or other common CAD model attributes. It represents surfaces as a mesh of triangles, a method known as tessellation. This approach is used extensively in computer graphics and is well-suited for the layer-by-layer processes of technologies like fused deposition modeling and selective laser sintering. The format exists in both ASCII and the more compact binary file versions, with the latter being predominant in industrial use due to its smaller file size. Its conceptual simplicity allows it to be generated by virtually all modern computer-aided design software packages, from Autodesk Inventor to SolidWorks.

History

The STL format was developed in 1987 by 3D Systems, the company co-founded by Chuck Hull, the inventor of stereolithography. It was created specifically to serve the data needs of the company's early stereolithography apparatus machines. As the first commercial rapid prototyping technology, stereolithography's success propelled the STL format to industry-wide adoption. Throughout the 1990s, as competing technologies like laser sintering from EOS GmbH and inkjet printing from Stratasys emerged, they all utilized the STL format for model input. Its status was cemented by its inclusion in the initial specifications of the RepRap project, which catalyzed the modern open-source 3D printing movement.

File format

An STL file describes a raw, unstructured triangulated surface using the concept of facets. Each facet is uniquely defined by its three vertices and a unit normal vector, which indicates the outward-facing side of the triangle. In the ASCII version, this data is stored as plain text, beginning with the keyword `solid` and containing repeated `facet` and `vertex` commands. The binary file version stores the same data in a more efficient, fixed-block structure, starting with an 80-byte header often used for comments. A critical limitation is that the format does not inherently ensure manifold geometry, which can lead to errors like non-manifold edges or zero-thickness walls that must be repaired by software such as Netfabb or MeshLab before printing.

Applications

The primary application of the STL file is in additive manufacturing, where it acts as the bridge between digital design and physical fabrication. Slicing software, such as Ultimaker Cura, PrusaSlicer, and Simplify3D, reads the STL file to generate the G-code instructions that control the path of the printer's extruder or laser. It is used across all major printing technologies, including digital light processing resins, metal powder bed fusion systems from companies like SLM Solutions, and binder jetting processes. Beyond manufacturing, the format is also commonly used for simple geometry exchange in finite element analysis and for preparing models for computer-aided engineering simulations.

Related technologies

While STL remains ubiquitous, several newer file formats aim to address its shortcomings. The AMF format, standardized by ISO/ASTM 52915, supports color, texture, multi-materials, and lattice structures. 3MF, developed by the 3MF Consortium whose members include Microsoft and Autodesk, is a modern, XML-based format designed to be fully comprehensive for additive manufacturing. In the realm of computer-aided design, native formats like STEP and IGES are used for precise geometry exchange, while formats like OBJ and PLY are common in 3D scanning and computer graphics for storing color and texture data alongside mesh information.

Category:Computer file formats Category:3D computer graphics Category:Computer-aided design