While all additive manufacturing technologies work differently and each have their own specificities, a printing process always starts the same way: Computer Aided Design. This step consists of modeling a part in two or three dimensions, so this is where the geometric shape of the part is determined. Once the 3D model is completed, it is necessary to export it to a file that can be read by a slicer, a software that acts as an intermediary with a 3D printer. And at that time, several choices are presented to the user. Between OBJ, STL, PLY, 3MF and many others, it can sometimes be difficult to choose between the different formats offered. To learn more and find out what the advantages and disadvantages of certain files are, we took an in-depth look at STL and 3MF files, probably the most popular among additive manufacturing enthusiasts.
Launched in 1987 by 3D Systems, the first company specializing in 3D printing, the STL format is today the most widespread on the market. Acronym for stereolithography (or Standard Triangle Language), it is present on the majority of platforms offering 3D models, such as Thingiverse, MyMiniFactory or Cults. Much more recent, the 3MF format was developed by a consortium led by Microsoft. Released in 2015, the format seduces today with some of its specificities. Also called 3D Manufacturing Format, 3MF models are intended to be intelligible and are intended to limit errors during the printing process.
Characteristics of STL files
Since its creation in 1987, STL has been the most popular format with 3D printing users, in particular thanks to its age. Compatible with all slicers as well as with all CAD software, STL files are mainly used today in the rapid prototyping industry. As the Standard Triangle Language acronym implies, the format “replicates” each pattern using triangles. In other words, the STL format recreates a 3D model by getting as close as possible to its shapes using thousands of triangles. More concretely, a flat surface composed of 4 sides is necessarily divided into 2 triangles. Thus, if we take the example of a cube, it is divided into twelve triangles, since it has 6 faces.
The amount of triangles also helps establish the degree of accuracy of the print. Modeling a face, for example, requires many triangles. All of these triangles are intended to come as close as possible to the shape defined by the 3D model. However, they do not contain any information regarding the manufacturing process, material, texture or color. And it is precisely here that one of the main limitations of the STL format lies.
Despite a very large volume, STL files only contain information to establish the geometry of a part. By going through a slicer, the user can nevertheless add different printing (slicing) parameters to the model/STL file. These will then only be recordable in 3MF format.
Another issue with STLs is the frequency of damaged files. When a file is defective, which is regularly due to a problem occurring during the conversion, the user is forced to repair it. This is why, like Netfabb and Meshmixer, several repair software exist. They allow you to correct defects in 3D files. But using such software adds an extra step to the printing process. Finally, the STL format is unreadable by humans, only compatible software is able to understand it and therefore interpret it.
Characteristics of 3MF files
Much more recent than the STL format, the 3MF is the result of a consortium launched by Microsoft bringing together Dassault, Autodesk, Stratasys and Ultimaker, among others. At its launch, Adrian Lannin, executive director of the 3MF Consortium, revealed the objectives of the project: “3MF will allow users of the technology to optimize productivity and unlock the functionality of 3D printing.” Designed to offer professionals a viable solution for storing 3D files, the 3MF format is distinguished by its light weight and the large amount of information it contains.
The 3MF file, unlike the STL, is not just a mesh. It is an archive file (similar to .zip) containing both the 3D model (in the form of a mesh) and information relating to the manufacture of the model, such as manufacturing methods, materials or even assemblies. On this subject, Microsoft explains: “3MF is a file format specially adapted for 3D printing and Windows. 3MF includes colors, textures, scale containing recommended print options, and many other improvements.” Moreover, a 3MF file is encoded in XML which makes it intelligible by a human and not only by a machine. Thus, if the .3MF extension is replaced by a .ZIP extension, it is possible to open each file of the archive to discover its characteristics. En addition to its openness (easy readability), it is also more intelligent since it offers a better understanding of mesh errors. It thus makes it possible to avoid problems related to geometric varieties (manifold) which prevents self-intersections, “non-manifold” models and holes in the mesh.
Currently, the main limitation of the 3MF format is not its properties, but rather its lack of popularity. Despite the various constraints related to its characteristics, the STL is today much more democratized than the 3MF. We notice this phenomenon in particular on the various sharing sites, such as Thingiverse, Cults or Printables. And other disadvantages persist. For example, there is a lack of integration within certain slicers and CAD software, which are currently incompatible with this format. We also notice a lack of intercompatibility between the slicers, some parameters configured in a slicer will not necessarily be transferred to another slicer when opening the same project. However, it is to be hoped that in the future, if 3MF gains popularity, efforts will be made to address these issues. Especially since it is an archive file with XML code, and can therefore be improved. We can thus imagine intercompatibility making it easier to share files that can be correctly interpreted by different slicers.
The concrete benefits of the 3MF format
Imagine you own a 3D printer and want to print a complex model. If you need outside help, from a printing service for example, they can configure the model in slicing software with all the appropriate parameters and then export this configuration in 3MF format. Thus, you will find in a single file your model, but also the printing profiles, the possible modifiers and other parameters. In the same case, using the STL format, the manufacturer would have had to export the print profiles in addition to the mesh, but even sharing these profiles, information like modifiers would be missing.
Now imagine that you are a designer wishing to share his 3D models on the internet, on Thingiverse, Printables or Cults, for example. By using the 3MF format, you can embed information related to materials or modifiers simplifying the 3D printing process. The 3MF format also allows you to define the license and associated copyrights. You can also add your name and description to the file. So, since all of this information is stored in the file and not just on the download page of the site, if your model is shared outside ofOn the site on which you originally shared it, all this information will be kept.
3MF, the format of the future?
As you will have understood, in the future, it is a safe bet that the 3MF format will become the standard. Seduced by its properties, several technology experts have already adopted it. Charly Le Roy, co-founder of Polyfab, a company reselling 3D solutions and providing training, explains the reasons for this choice: “ The main difference in my opinion is the amount of information stored. An STL contains only the 3D model, its 3MF counterpart contains the model but also its orientation, its supports, its printing parameters… The 3MF is therefore much more practical for the needs of multiple iterations. An opinion shared by Michael P. Bourque, Director of Digital Manufacturing at Boston Engineering: “I can’t believe that STL is the most common format among 3D printing enthusiasts. STL is a terrible format for reproducing model geometry and is only used because the slicing step is fast. […] I prefer the 3MF because it is self-contained and can hold additional data to reduce problems.”
Due to its ability to limit the risk of error and facilitate model sharing, the 3MF format seems much more appropriate and could last over time. As a sign, the American giant 3D Systems, creator of the STL in 1987, decided to join the 3MF Consortium when it was launched in 2015. Charly Le Roy concludes: “ The format that will be used for sharing print projects through print-ready template libraries will definitely be 3MF. It naturally limits the risk of error and saves time when manufacturing parts. »
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Article co-written by Philippe Girardie and Elliot Saldukaite
*Cover photo credits: 3Dnatives