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ChristopherLewi12-Amethyst
12-Amethyst
December 20, 2016
Question

MBD Static Design Outputs cause concern for Assemblies

  • December 20, 2016
  • 2 replies
  • 2168 views

I'm wondering if you MBD practitioner folks out there can provide an opinion upon a point of view that is prevailing right now at my division regarding usage of models to document assemblies.

The 2D situation is that many assembly drawings are considered to not show so much detail of the underlying parts as to demand a new version is generated as sub-components are iterated. Thus it is currently deemed perfectly acceptable to have a 2D PDF of an assembly drawing that is technically built from an OOD configuration. We say things like 'the assembly drawing is only intended to act as guidance for assembling' and 'specs for lower level parts are controlled by separate lower level design outputs'

So now we fast forward to MBD or in our eyes 3D model based definition to be clearer. The same logic apparently results in a conflict because the definition of the assembly is much higher a viewer can e.g. isolate a single component and then end up 'confused' or worse. So the people who hold the previously discussed 2D opinion now 180 degree flip and demand a perfect 3D assembly. This of course is a major major headache with any static design output such as a 3D PDF or a STEP file. What the group is basically saying is that we have to either systematically in IT re-generate a new version of the design output to match the currently valid configuration OR we insist the users chase the creation all the way up the tree. Since our assemblies could easily have 7 levels of depth and a few thousand parts with multiple thousand changes during NPI, the number of re-creations for assembly design outputs becomes totally ridiculous.

Wondering if anyone else has faced the same logic and prevailed, found a technology that circumvents it or triages it.

Appreciate any conversation on this frustrating matter which is preventing us from leveraging the model beyond making an assembly drawing right now.

Chris

    2 replies

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    dschenken1-Visitor
    1-Visitor
    December 20, 2016

    The key is that the approved top level was only approved with as-released parts at the time the top level was itself approved. When there is a desire to roll the new parts into production then newly approved versions of the top level assemblies should be created.

    The best way to handle this is by block incorporation where a group of low level changes are incorporated at one time.

    Other than that it runs into the same problem as allowing alternate parts. The top level can't have all possible combinations of alternate parts installed at the same time, so one needs to handle it the same way as as-built by either building in blocks or creating individual serial numbered assemblies to track them individually.

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    ChristopherLewi12-AmethystAuthor
    12-Amethyst
    December 20, 2016

    You pointed out the other gotcha awaiting assemblies for sure with the alternate parts and the tendency for us to build 150% assemblies to avoid managing a bunch of additional cad structures. I think the block incorporation idea could have legs, i'll try that tack.

    R
    RaphaelCNascime1-Visitor
    1-Visitor
    December 20, 2016

    I agree that it has to do with the notion of assembly configurations (as-stored vs. latest).

    The published 3D PDF represents effectively the as-stored configuration at the time of publishing. To get the latest versions of the lower-level components requires retrieving the assembly in the latest configuration - which of course might differ from the as-stored configuration.

    I don't know exactly how your configuration and change management processes work, but it might be worth exploring whether those processes need to be reconsidered in light of an MBD approach before investing a lot of time and effort into the technical solution.

    Today, if someone is producing an assembly based on a released 2D drawing, where does the BOM come from?

    Because if the assembly is released at Rev A and it contains part 123 at Rev A and part 456 at Rev B, Then later, when part 123 gets revised to Rev B, does the next time someone produces the assembly do they automatically get 123 at Rev B and 456 at Rev B? That happens without revising the assembly to Rev B to account for the revised components? That seems odd to me because essentially without revising the assembly you couldn't really be confident that everything would work. It would also be hard to keep track of what actually gets produced because some assemblies built at Rev A might contain part 123 at Rev A and some might contain part 123 at Rev B. That's probably over-simplifying the problem and maybe I'm missing something...

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    ChristopherLewi12-AmethystAuthor
    12-Amethyst
    December 20, 2016

    Hey just a few notes adding to the background in case it helps others journeys.

    One of the main hopes we have for MBD is to save some time. I totally agree that we'll likely need to change up our expectations on the process front. Today we have a policy that latest released from the PLM is what we make. As-Stored would be woefully out of date quickly in our current ways of working. We generally hold firm on a policy that revs only are allowed post release if form fit and function are not primarily violated. However prior to release we'll rev away with all kinds of changes. I could imagine some form of compromise whereby the block release idea is done prior to release, then we insist on chasing the tree post release.

    Cheers for your ideas.

    Chris

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