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Into The 3D Printing File Format: STL, OBJ, AMF, 3MF

Mar 11, 2020

In order to help everyone understand the 3D printing format more fully, today I will share with you 4 kinds of 3D printing file formats: STL, OBJ, AMF, 3MF:

STL format

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Nowadays, 3D printers realize the conversion of virtual 3D data into solids, and the criterion for achieving all this is the STL file format. The STL file format has become the industry standard for CAD / CAM system interface file formats worldwide and is the most common file format supported by 3D printers.

There are two types of STL files: one is the ASCII text format, which is characterized by good readability and can be read directly; the other is the binary format, which takes up less disk space, is about 1/6 of the ASCII text format, and has poor readability. But whether it is ASCII text format or binary format, the STL file format is very simple, easy to generate and segment, and simple in algorithm. In addition, the output accuracy can also be easily controlled.

2. OBJ file

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It is a standard 3D model file format developed by a workstation-based 3D modeling and animation software "Advanced Visualizer". It is very suitable for data exchange between 3D software models. For example, if you build a model in 3dsMax or LightWave and want to transfer it to Maya for rendering or animation, exporting OBJ files is a good choice. OBJ mainly supports Polygonal model.

Due to the convenience of OBJ format in data exchange, most 3D CAD software currently supports OBJ format, and most 3D printers also support printing using OBJ format. As the STL and OBJ file formats still seem a bit too simple, they can only describe the surface geometric information of three-dimensional objects, and do not support the description of feature colors and materials on the surface. Therefore, the American Society for Materials and Experiments has released a new 3D printing file format AMF format.

3. AMF file

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Based on the "STL" format currently used by 3D printers, which compensates for its weaknesses, the new format can record color information, material information, and internal structure of objects. The AMF standard is based on XML (Extensible Markup Language), is easy to understand, and can be easily extended by adding tags in the future. The new standard can not only record a single material, but also designate different materials for different parts, and can change the proportion of two materials for modeling. The internal structure of the model is recorded with a digital formula, which can specify the image printed on the surface of the model, and also specify the most efficient direction for 3D printing. In addition, raw data such as author names and model names can be recorded.

Compared with the STL file format, AMF overcomes its shortcomings such as low accuracy, lack of process information, large file size, and slow reading. It also introduces concepts such as curved triangles, functionally graded materials, and alignment. Surface triangles can greatly improve the accuracy of the model. It uses the normal or tangent direction of each vertex to determine the curvature of the surface. During data processing and slicing, the surface triangles can be subdivided to obtain the desired accuracy.

The expression of the material composition in different regions is expressed by the coordinate formula of the space point. The material mixed according to a constant ratio is a homogeneous material, and the ratio that changes linearly according to the coordinate value is a gradient material, and a nonlinear gradient material can also be expressed. Therefore, the AMF format contains more complete process information, smaller file size, and fewer model errors, which makes it easier to use in the 3D printing process and the model design process is easier.

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How much improvement does the AMF file format have over STL, OBJ, and other file formats:

    1. Technical independence: The file format generally describes an object so that any machine can use it. Resolution and layer thickness are independent and do not include any manufacturing process or any specific information technology

    2. Simple: The AMF file format is easy to implement and understand. You can use a simple ASCII text viewer to read and debug. The same information is not stored in multiple places.

    3. Scalability: The complexity and scale of the file format are related to the resolution and accuracy of the 3D printer. AMF files can handle the same objects in large arrays, reducing internal complexity.

    4. Performance: The file format enables reasonable read and write operations to provide detailed performance data contract attachments for typical large files.

    5. Backward compatibility: Any existing STL file can be directly converted into a valid AMF file without losing any additional information. AMF files are also easy to convert back to STL using legacy systems, although functions such as color and texture will be lost. This format effectively maintains the triangular network, and uses geometry to optimize the existing segmentation algorithms and codes for infrastructure.

    6. Future compatibility: In order to remain useful in a fast-growing industry, this file format is easily technically extended and compatible, and it allows new features to be added while ensuring technological progress.

4.3MF format

Compared to STL with too few functions, AMF seems to have too many functions, so Microsoft and HP, Autodesk, 3D Systems, Stratasys and other giants formed a 3MF alliance to launch a new 3MF format. The 3MF format can more fully describe 3D models. In addition to geometric information, it can also maintain internal information, colors, materials, textures and other features. It is also an XML-based data format, which is extensible. The file format can describe the 3D model more completely. In addition to geometric information, it can also maintain internal information, colors, materials, textures and other features.

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For consumers and practitioners using 3D printing, the big advantage of 3MF is that big brands support this format. Other companies in the 3MF Alliance are Microsoft, SLM, and HP, and Shapeways also includes providing insights in the context of 3D printing. Other key players in the 3D printing and additive manufacturing business, such as Materialize, 3DSystems has recently joined the alliance. Under the support of these giant companies, the 3MF file format with the same performance as the AMF file format has gradually replaced the AMF file format, which is also a crisis of the AMF file format.

Just like why most pictures are in jpg or gif format, STL is adopted by the majority of 3D printing manufacturers. This is actually a question of historical legacy and people's long-term usage habits. The STL format has been deeply entrenched in people's hearts, so if other formats want to be "upper-level" or even widely adopted by the majority of 3D printing manufacturers, it may take some time. The various file formats will be "who is dead" in the future, yet to be tested by the market .