3D PDF for Mission Critical Design information (Inside MIL-STD-31000B)
By Christine Longwell
In the battle for market dominance all the leading CAD companies have fought to have their file format declared victorious. Interoperability, which sounds brilliant to most technical users, just isn’t a large priority in the CAE industry where software from different vendors use different numerical geometry calculation engines (called software kernels) to determine how each part and assembly should be rendered. As difficult as it is to open files from one CAD package into a different CAD package with reliable results, people often forget that a certain amount of error should be expected when upgrading files from one version of CAD to another.
At the risk of sounding like an antique, I admit that I still have my original college laptop sporting a Pentium 2, 266 MHz processor with 4 whole GB RAM and SolidWorks ’98. Reason? Well, it has my college design project on it, and I am a digital packrat. If I somehow magically got the files off that dusty old hard drive:
Were my modeling techniques robust enough to retain their parametric links to the drawings? I was a pretty good CAD jockey back in my day, but some of my partners… it was questionable.
Would they resolve properly in today’s software 24 years later? Each new release of software includes better more accurate error resolution that will raise flags if the user tells the software to do something questionable. This leads to errors during the upgrade process.
What would be an acceptable error rate when I reopen my model?
Assuming a project is simple with only 100 parts
Assuming each new release of software opens 99.7% of historical models successfully (which is conservative)
SolidWorks has a new release every year…
That is still a 7% overall failure rate. It’s a good thing I didn’t design passenger planes!
Clearly relying on native CAD geometry has risks when different users have various CAD systems, but these risks compound over time. As flat, 2D drawings began to be replaced with 3D, easier to comprehend digital models, issues such as accessibility and interpretation became a real concern. Enter the need for industry standardization.
For this new digital world to effectively replace physical archives these digital files need to be:
Software agnostic – These files need to be easily opened on any operating system without access to specialized programs.
Capable of interaction and annotation - dimensions, tolerances, and features are served to the user rather than measured by the individual user. This enables the author to specifically convey the intended design attributes.
A container for references - Can include other files that can be accessed separately, such as specification documents, spreadsheets, and native, neutral, and viewable 2D and 3D models. (most commonly *.step)
Rather than create a new file format for 3D data manufacturing companies realized that they could leverage the well accepted PDF (Portable Document Format) files. Embracing a standard format is particularly essential when designing for the Aerospace & Defense industry where more emphasis is put on delivering intellectual property than physical parts.
To take the guesswork out of how to acceptably submit TDPs the Department of Defense issued MIL-STD-31000B which details the specifics of how to properly submit 3D PDFs for these design contracts.