The STL file is the current popular file for 3D printing. Now, this file form is gradually being replaced by the 3MF format. STL is a kind of 'old' 3D file format, which was first published by 3D Systems in 1987. It is the abbreviation of Stereolithography. The STL file is designed to take into account the case of additive manufacturing, the data (usually based on NURBS or BREP) is converted to grids for 3D printer analysis. Therefore, curves and composite surfaces are converted to machine data running code. STL uses small triangles to simulate the original surface of the model. The more complex and detailed the structure is, the more triangles are needed.
△ The more complex and detailed the structure is, the more triangles are used.
STL file of ‘tradition’
The STL file describes the original, unstructured triangularine surface by using the unit normal and vertices of a triangle in a three-dimensional Cartesian coordinate system (sorted by right-hand rule). The natural file format of this machine is a series of closed polygons (layers or slices) corresponding to different Z values. However, since the layer thickness can be changed, STL can be simulated in a faster but less accurate way, defining the build model as a collection of closed polyhedrons sliced horizontally. However, STL, after all, based on grid architecture, cannot store information as mathematical expression. Therefore, only the original information can be carried over. This leads to it needs to occupy a large hard disk space in storage, and does not cause damage to the geometric structure of the model itself.
△ Under the same shape, the CAD format is shown as a ring (shown as two concentric red circles), STL is composed of triangular planes.
In addition, STL does not carry any machine information, print settings or any other useful information needed to recreate files. Therefore, when manufacturing parts with teams or third parties, STL and manufacturing specification list need to be attached together. Despite all the flaws, STL has become the most popular 3D printing file format, The reasons are as follows:
The Rise of 3MF
3MF is a new file format, which is developed by the company alliance to promote 3D printing ability and technology. It is considered to be a revolutionary and special form. 3MF brings improvements equivalent to switching from BMP to PDF: 3MF carries more information, including unit information, color and texture information for multi-jet printing, relative positions in space, and so on. STL has no unit, even if the two file formats carry the same amount of data, 3MF file is still much smaller than STL file.
△ Import Fusion 360 grid workspace 3MF file. There is no unit tab in the right dialog because the 3MF file contains this information.
The 3MF file uses human-readable XML format (Extensible Markup Language), so you can store a large amount of data needed by the machine without accompanying print settings in separate files. Users can even open XML to read execution actions and modify code directly. This not only provides diversity, helps prevent printing errors, but also helps reduce file size. While 3MF does not need repeated data in batch processing of the same components, and even allows users to save and share the desired slice configuration, and save time.
△ The same data imported by STL lacks color information, and the dialog box requires the user to define the unit size.
3MF can also display details of parts :
Role of manufacturing processes:
3MF format can carry metadata for printing settings and machine information, which also requires a slicer independent of a specific machine. For example, Fusion 360 ' s additive manufacturing space covers all the above settings and allows STL and 3MF files to be exported. This can help users to keep all manufacturing data in their place : to concentrate all relevant design data.
△The 3MF exported by Fusion 360 shows two tabs of metadata.
At the same time, accessing print settings and machine information also means that you can completely control your supporting structure and use a single file to transmit information to the printer. This is impossible for STL, unless optimization techniques are used additionally. 3MF can also bring security protocols to manufacturing data, for example, it can limit the number of copies of parts manufactured by machines. This secure content extension provides a mechanism to encrypt sensitive 3D printable data, which helps protect intellectual property rights, reduce risks and ensure that companies comply with government regulations.
Other 3D print file formats
Besides STL, OBJ is also a very common file format, which can store texture and color information. And PLY format (Polygon format) is often used for 3D scanning object files. In addition, like 3MF, AMF format is a new 3D printing file format, which can record color information, material information and internal structure of objects, and also adopts XML format. Although AMF has the potential to become a new generation of 3D printing data standard, it is hard for AMF to have no giant support.
△ Same model, comparison between STL and 3MF
In contrast, the members of 3MF Alliance include Microsoft, AutoDesk, Dassault Systems, Netfabb, SLM, HP, Shapeways, all of which are industry leaders. With the support of Microsoft WIN8.1 and WIN10 for 3MF printing format, 3MF may gradually replace STL and become a new generation of 3D printing standard format in the future.
