3D printing is a technology that is rapidly expanding into every industry to overhaul the way that traditional manufacturing, prototyping, media and design is done. The application of 3D printing was founded in the 1980’s, but only recently has the development of new materials and processes made it a viable option for companies to implement it in their engineering process. As more companies adopt this revolutionary technology, the importance of understanding 3D part design using SOLIDWORKS for 3D printing increases with it.
STL files and how they work
STL files were the initial file format developed for rapid prototyping, and it is still the most widely accepted format today. The simplicity of the file format makes it easy for nearly all CAD programs to output thus making STL files the universal standard.
STL files were originally developed in the 1980’s with the initial development of the first 3D printers. The first 3D printing technology was known as Stereolithography which is where the file format term STL comes from. Since then, many backronyms have been associated with the file format. The backronym “Standard Triangulation Language” is a more accurate description of the way the file format works. Essentially, STL files eliminate all other data (color, material, texture, etc.) associated with a SOLIDWORKS model other than the surface features. When the file is output as an STL, the software then replicates the surfaces of the model using series of collinear triangles.
So now you have your CAD model and you want to take steps towards actually printing the model. Probably the easiest of the steps is saving the model as an STL file. With your model open in SOLIDWORKS, go to File>Save As to open the save directory. Use the drop-down menu next to “Save as type:” and select STL (*.stl). This will now save a new file of your model as an STL file with the default option settings. The options are the most important aspect of the way the print will result when it comes to the software.
Why do the options matter?
Most of the time you can save an STL file using the default options and the print will turn out fine to the naked eye, but if your company has invested in an industry leading Stratasys 3D printer that is capable of printing down to the micron resolution level then why not get the most out of your machine? This is where tweaking the options of your STL file can make all the difference. These options essentially control the accuracy of the triangulation model. To visualize this, imagine a perfectly round sphere that is converted to an STL file. When converted, the triangles are used to model the surface meaning the size of the triangles determines how coarse or smooth the surface of the sphere appears.
This is why controlling the options can be the difference between a poor print and a quality print. Users typically take this advice as reasoning to crank the resolution of the STL file to highest possible settings, but doing so can make the file unmanageable by the printing software - especially, if it is a complex part with many faces and grooves. It is important to find the proper balance between a high-resolution STL file and a file that is manageable by the software.
How to find the right balance
ASCII or Binary
The first option that you can choose from is the option to save the file as ASCII or Binary. For nearly every application, Binary is the primary choice because the file size is 6 times smaller than ASCII and the quality of the file is the same. The only advantage to ASCII is the ability to visually read and check the file.
Deviation & Angle Tolerances
The resolution settings within SOLIDWORKS are limited to two default options which are coarse and fine as well as the ability to do custom settings. The custom settings option is the most powerful tool available to adjust the quality of your resulting prints. The typical response is to crank up the deviation tolerance and angle tolerance thinking that this will ultimately produce the best print, but the true limitation of the print quality is the 3D printer itself. For high-end Stratasys 3D printers that have superior layer resolution, a low tolerance level is acceptable because the printer is capable actually printing the output STL resolution. Deviation is considered a linear dimension that refers to the maximum offset that the triangular facet of the STL file is allowed to be from the original modeled surface. The angle tolerance refers to the angular deviation acceptable between adjacent triangles. Essentially, these two options control the number of triangles used to model the surfaces. There is a downside to adjusting these options to their max settings though. The more triangles involved with modeling means a larger file size thus making it difficult to handle and possibly unnecessarily large. Some geometries are not complex enough to require a high-resolution STL file to be printed at the same quality as a low-resolution STL File.
Which settings to choose?
The limitation comes from the resolution of the 3D printer itself which means that finding the right balance of STL settings will come from a natural intuition based on the geometry and orientation of the part when it prints. Because there are so many printers to choose from these days, my professional advice is to research the specific 3D printer that is being used to find advice on the best resolution to choose.
By: Peter Kootstra, 3D Printing Applications Engineer