It’s important for product owners to understand the different file types associated with 3D CAD Modeling while collaborating with a CAD designer. Every commercial CAD program has its own native file types. These contain the most information but can be difficult to share. STEP and IGES files are used to share data between different CAD programs. STL and DXF files can be used to export data from CAD to equipment like 3D printers or laser cutters.
One important phase of the product development process is 3D CAD Modeling, where engineers use software to model the fine details of your product in 3D and generate files to provide to manufacturers. Usually, product owners rely on their designers to generate and manage these files. However, since these files are an important deliverable for your project, product owners should understand what the many different types of CAD files contain and are used for.
Native CAD files
When a CAD Designer is working on a project, their system will actively create, edit, and save the native files for that program. These file types and their extensions are specific to the program.
- SolidWorks: *.sldprt (Part files), *.sldasm (Assembly files), *.slddrw (drawing files)
- NX/Unigraphics: *.prt (Part, Assembly, and Drawing)
- CREO: *.prt (Part and Assembly)
- Autodesk Inventor: *.ipt
For any product, the native files are the “purest” version of its CAD. These files will usually contain all the design history and are the only version that’s fully editable.
However, sharing these files from one designer or system to another is no easy task. These files are not cross compatible (for example, it’s impossible for a SolidWorks system to open native CREO files). It can even be difficult to exchange CAD files between systems with the same commercial software. This is because native CAD files contain active references to each other based on the file names and file paths on the system they were originally created with.
At Emergnt, we use SolidWorks for 3D CAD Modeling in mechanical product design. Since SolidWorks files are often part of our deliverables, I’d like to go into some more detail on the native SolidWorks file types.
A Part file (*.sldprt) contains a single 3D model as defined by a series of “features”. These features are the input steps taken by the designer to create the model and usually involve translating two-dimensional geometry into some three-dimensional form. With access to the design history, a SolidWorks designer can not only understand how the original designer defined the model but can also make edits to the model without recreating it from scratch or breaking its external references.
An Assembly file (*.sldasm) is a 3D file where separate part files or assembly files (“subassemblies”) are grouped. Within the context of an assembly file, the designer defines “mates” to link features and geometry from one part to the other, reflecting how these parts might be assembled in space. The typical result is a collection of smaller 3D models combined into one larger 3D model with defined orientations and positions. For products with multiple parts, the “top-level” assembly files (containing all the parts and subassemblies) might be considered the most important CAD file.
A Drawing file (*.slddrw) is a used to create two-dimensional files which can be populated with 2D views of part or assembly files. Drawing files are typically used to create Production Drawings (or PMI Drawings), which are the industry standard reference for manufacturing. Drawing files actively reference the part or assembly they view and are populated with dimensions, tolerances, and other notes about the product (called “callouts”).
Pack & Go
Pack & Go is a feature built into SolidWorks and other CAD programs to help share files with references between compatible systems. Using Pack & Go, a designer can “pack up” all of the parts, assemblies, and drawings with their references into a folder or zip.
At Emergnt, we like to provide our clients with a Pack & Go at the end of their project. We let them know that any SolidWorks designer can open this to access and edit all of their files with the full design history.
eDrawings is a free viewer developed by the makers of SolidWorks. SolidWorks parts, assemblies, or drawings can be exported as *.eprt, *.easm, and *.edrw files (respectively) to be opened in this program. This program contains useful tools that many other free CAD viewers do not, like tools to measure feature dimensions and calculate the weight of parts.
At Emergnt, we frequently recommend our clients install eDrawings to conveniently review their CAD files.
Other File Types
In light of the difficulty sharing native CAD files due to compatibility and file references, CAD designers often export their work to these other file types when sharing files.
STEP (‘Standard for the Exchange of Product Data”) is one of the common CAD file types used today. This file type is specifically intended to circumvent the compatibility problems with native CAD files. *.step files are used to export both part and assembly files and can be opened by virtually any CAD system.
Step files contain exact copies of the model geometry from their native counterparts. However, STEP files do not include design history. This means that it may be difficult for a designer to edit part files that they received as STEP.
Also keep in mind that, since both parts and assemblies can be exported as STEP files, these different file types will have the same common file extension. When receiving a collection of STEP files, be sure to ask your CAD designer which is the “top level assembly”.
IGES (“Initial Graphics Exchange Specification”) is a file format used to represent and exchange 3D geometry data. *.iges files are similar to STEP files in that they were developed to share data between incompatible CAD systems. There are some key differences. STEP files are more modern and support a wider range of geometry and metadata, but they are also larger and more complex. IGES files are generally easier to work with but may not support as much information. At Emergnt, we tend to favor STEP files but use IGES to transfer very large files as a smaller file size.
STL (‘Stereolithography”) is a file format used to represent 3D geometry. It is a popular choice for 3D printing because it contains only the surface geometry of a 3D model, with no color, texture, or other attributes.
Important note regarding *.stl files: These are not exact copies of the models from the native CAD files. The surface of the models is approximated using a series of triangular “elements”. The designer sets the density of this mesh, which controls the accuracy of the model and the file size, when exporting the file.
DXF (“Drawing Exchange Format”), is a file format used to share 2D geometry in CAD. It was developed by Autodesk and is widely used for exchanging data between different CAD systems. DXF files are commonly used by manufacturing equipment that works or cuts in 2D, like a laser cutter or a waterjet cutter. When working with sheet metal parts, we provide our production partners with a *.dxf “flat pattern”, which they can use as a direct input for their laser cutter.
With all the files and file types, managing CAD can be confusing and daunting for product owners. Different situations will call for different file types, and sharing the wrong file type can cause delays in your product development cycle. Best practice is to work with a knowledgeable and trustworthy design firm like Emergnt Design Labs to be sure you’re getting all of the right data in the appropriate formats.
A product design expert, Jeremy cultivated his skills working in manufacturing and rapid prototyping facilities. His design experience ranges from consumer products to government contracting, and he is known for end-to-end support on every project.
M.S. in Mechanical Engineering, Georgia Institute of Technology.