PTC : An Unexpected Lesson in Faster CAD Assemblies

At LiveWorx 19, Pete Hollmer from Raytheon delivered an immensely compelling presentation with the provocative title 'The Worst Assembly in the World.'

The objective was to take an assembly of medium complexity, which regenerated in about a minute, and get it to take over an hour to complete by making inadvisable changes to it.

Pete used a dozen different methods and evaluated the impact. It's an interesting study of which product design techniques had the worst effect on regeneration time - and file size as well.

The most interesting lessons for me were the practices that I always believed adversely impact regeneration time, but don't - or at least not anymore, due to improvements in the Creo Parametric software:

Slide from Hollmer presentation: Adding extruded threads and slots, surprisingly, saved assembly load time!

• General Patterns. From fastest to slowest regeneration, there are three options you can choose for a pattern: Identical, Varying, and General. Changing the patterns in Pete's assembly to General had a minimal impact on regeneration time, which might explain why PTC changed the default setting to General a few versions ago.
• Extruded Text, Threads (Helical Sweeps), and Slots. These features create small edges and surfaces, which nominally would be bad for regeneration. Surprisingly, these part features did not slow down the assembly.
• Circular References. These have always been the bane of designing with external references, which is a powerful assembly modeling technique and the basis of top-down design. If you set up references incorrectly, you can accidentally make an object both the parent and child of another object-that's a circular reference. When Pete forced circular references into the demonstration assembly, though, the impact on regeneration was much less than I expected. Anecdotally I have noticed that it's harder to make circular references today compared to even Creo Parametric 2.0, but I'm certainly surprised that they don't blow up regeneration time like they used to.

Here's what did have an extremely adverse effect on regeneration time:

Slide from Hollmer presentation: Autorounding knurled patterns slowed the assembly significantly-a warning to use features properly.

• AutoRounds. When placed on knurling (patterns of left-handed and right-handed helical sweeps--see the PTC Learning Connector video) on some parts, these small fillets blew up the regeneration time. This is a great warning that while the AutoRound feature is extremely powerful, it's incumbent on the user to ensure it's used properly.
• Assembly Cuts. This did not surprise me. I've always told people not to use assembly-level features unless you truly need to model match-drilled holes and cuts that are performed at the time components are integrated. Just like Pete, I've advocated turning off Automatic Update and Advanced Intersection if you must use them, but I was previously unaware how deleterious the Through All depth option was for them.
• Graphics Settings. Creo Parametric contains a number of configuration options and session environmental settings for controlling things like anti-aliasing, shade quality, and display of small surfaces. I had no idea that these settings and choice of display mode (like Hidden Line versus Shaded or Wireframe) could double the regeneration time of an assembly.

Now when I get back to my day job, I know that I have to:

• Make a bigger effort to have our end users employ inheritance features over the one-component assemblies with assembly cuts.
• Optimize our graphics settings.
• De-emphasize pattern options and surprisingly circular references as culprits of bad regeneration.

Pete's presentation is well worth watching, and I'm sure I'm not the only person in the audience with significant experience who learned something. For me, this gets to one of the core benefits of attending LiveWorx. After each conference I always come away with more knowledge I can share back home than I expected, and it reminds me that there are always opportunities to learn and improve.

You can see Hollmer's full presentation by visiting the LiveWorx 2019 Digital Engineering archive. First time visiting? Register for access and once logged in, navigate to the 'Digital Engineering' section, select 'Thursday, June 13th, 2019,' find 'The Worst Assembly in the World,' and then click Video.

Dave Martin

Dave Martin is a former Creo, Windchill, and Mathcad instructor and consultant. After leaving PTC, he was the Creo specialist for Amazon; and a mechanical engineer, Creo administrator, and Windchill administrator for Amazon Prime Air. He holds a degree in Mechanical Engineering from MIT and currently works as an avionics engineer for Blue Origin.

Martin is the author of the books Design Intent in Creo Parametric and Top Down Design in Creo Parametric--both available at www.amazon.com. He can be reached at [e-mail].