INTRODUCTION TO CAD FILE FORMATS

Audio: Introduction to CAD file formats

One of the most important things when working with any software (including CAD software) is the ability to save your progress, continue from where you stopped the last time, and, once you are done, share your work effectively. Usually, this is overlooked and taken for granted until you either lose your files or receive important files that you cannot open. For this reason, we will dedicate this article to different CAD file formats to really understand how important they are and what types we have.

Importance of CAD file formats

File formats contain different information that helps your computer understand what to do with it. Information that is stored in the file will tell your computer which type of programs can open and work with that files. File formats, when they are opened in their native program, can be opened and edited by a native program or other programs that have the ability to read this type of format. The file name usually includes a file extension that indicates the format itself.

Here is what the .step file looks like when opened with Notepad:

For example, a document with the extension “.docx “indicated that this is an MS Word document in the XML-based format. In the same way, a CAD file has its own extension that tells a computer with which program it should be opened.

In addition to helping your computer understand what to do with your file, CAD files are important because they:

Ensure that all the relevant design and manufacturing data is properly stored – imagine that you work 10h on your design and you save your progress in CAD file format that only saves every second feature you use. Or that it is not capable of saving the dimensions on engineering drawings. It is extremely important that all of the relevant design and manufacturing data is properly stored in a file format of your choosing.
Ensure design history and revision control – CAD files enable you to go back in your design and change if something needs to be changed. It would be an extreme waste of time that you must start from scratch every time you want to update something. Furthermore, you can see the previous revision you created in case you want to return to one of the previous iterations. It is also useful in cases when you want to see design history and changes that were made over time.
CAD files improve the collaboration between different teams – in collaboration with PDM software, CAD files make it easy to exchange data between different team members. Furthermore, with the help of PDM software, team members will always have access to the latest and most up-to-date design files.
CAD formats ensure compatibility between the different CAD software – some CAD formats can be read by non-native software. In cases where this is not possible, we have “standard exchange formats” like .step that can be used to import design data from one CAD software to another.

Native CAD file formats

Each CAD software typically uses its own file format to store and exchange data. These native file formats store the complete information of the CAD model, including geometry, dimensions, materials, assembly structure, and other design features. Native files allow users to fully edit and manipulate the design within the software that created them. Part CAD file formats are used to store relevant design and manufacturing data for parts (components) created in CAD software. The same logic is behind the assembly and drawing of CAD file formats.

Let us look into some of the native CAD file formats specific to different CAD software:

CAD software	Part file extension	Assembly file extension	Drawing file extension
NX CAD	.prt	.prt	.prt
Catia V5	.catpart	.catproduct	.catdrawing
SOLIDWORKS	.sldprt	.sldasm	.slddrw
Autodesk Inventor	.ipt	.iam	.idw
Autodesk Fusion 360	.f3d	.f3d	.f3d
AutoCAD	.dxf	.dxf	.dxf, .drw
PTC Creo	.prt	.asm	.drw

Standard exchange formats

Standardized file formats facilitate the exchange of CAD data between different software applications. We usually export or import these files into our CAD data, but they are not native CAD file formats.

Let us look into some of the standard exchange formats that you may work with:

STEP file (Standard for the Exchange of Product) – is an international standard for the exchange of product data in a neutral and vendor-neutral format. It is developed and maintained by the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). ISO 10303-242 specifies the application protocol for model-based 3d engineering. STEP file format includes information regarding shape (3-D by default), design, manufacturing, quality assurance, testing, maintenance, etc.

DXF file (Drawing Exchange Format) – contains 2-D and 3-D geometric and topological information, layer, line color, and text.

IGES file (Initial Graphics Exchange Specification) – exchanges primarily shape (both geometric and topological) and non-shape data, referred to as CAD-to-CAD exchange.

STL file (Stereolithography or Standard Tessellation Language) – usually used for 3D printing. The STL format represents the surface geometry of a 3D object using a collection of triangular facets.

PDF file (Portable Document Format) – preserves documents’ visual integrity and formatting across different devices and platforms. PDF files are widely used for sharing and distributing documents because they retain the original layout, fonts, images, and formatting, regardless of the software, hardware, or operating system being used to view them. Usually, you will export your drawings from a native file to a pdf file for easier sharing with other people.

3DPDF file (3D Portable Document Format) – enables inclusion of interactive 3D models with a PDF document. This format is useful for design communication with people that do not have access to the CAD viewer software.

Closing words

CAD file formats ensure that our design and manufacturing data are safely stored. We are going to communicate with multiple teams and people, and we will have to exchange files with them. CAD software has the option to convert native data to non-native data. Usually, it is called “export, “or we can use the “save as “option to save the data in the desired format. For example, we can convert native drawing files to pdf format. Or native-part file to STEP file. These are all neutral files that can be opened with many standard available software.

One of the things that I always suggest is that as soon as you start working in CAD software, enable the autosave option. Furthermore, when you start a new design, immediately save the file so that your progress is saved in case of a software crash or power shortage.

Now you have an excellent overview of CAD file formats. However, I suggest you go through the text once more and identify areas you think need more understanding and clarity. Then, once you have identified those areas, start building up your knowledge in those areas.

To make it easier for you to find related posts, check the “Further reading” chapter below. Do you have any questions or need something to be clarified better? Leave a comment below, and I will give my best to adjust the post accordingly.

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