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Top-Down Modelling without External Reference?


Top-Down Modelling without External Reference?

Hello all,


I am wondering if it is possible to import a master model to a part without creating an external reference to the master model? So, rather than importing the geometry with a reference to the master model which would update when changes are made to the master, you would import the master, break the external reference on the import and be left with a direct model which will not update when the master is modified.


It's worth mentioning the reason behind my question. I am working on a model which will ultimately need to be stored using a document control system or PDM. The parts have been built using a top down approach and as such can not be stored independently from the assembly in which they were created. Am I correct in assuming that most doc control systems/PDMs are not compatible with the top down approach? The parts in question have only referenced the master model and no other part in the assembly, therefore external references are well managed and lead back to the same source. Despite this, to store the parts on the PDM without failed features I would have to store them with the assembly which includes the master model leading to duplication of parts on the PDM since the master is referenced by multiple parts in the assembly. The obviously solution is to build the parts bottom-up, however that would involve redoing a significant amount of work and hoping that a feature is not overlooked on the rebuild which is less than ideal. Essentially I am wondering if anyone has a bets of both worlds type solution for the quagmire I find myself in which will not entail redoing past work?


Thanks in advance,


This is a long running difficult discussion regarding the philosphy of data management.


On one hand - the relationships are crucial for design / updates / where-used/affected types of interactions - mainly in larger designs or where you have large groups of people doing things in multiple areas of a design that need common references.


On the OTHER hand - when a product is "done" and needs to be released for manufacture, maintenance and publication.... all that "baggage" is not really useful - kind of a pain to deal with... and can affect item reuse for "frozen" things that rarely require high level change with a trickle down affect.  (e.g. Class-A surface change, or skeleton references).


We had a customer asking about this very issue a few months ago... We coded up something in Nitro-CELL to basically loop through each model and break the external reference relationships as they were found.  This left them with a pile of parts that they could independently manage in PDM/PLM.  Which was their intent.


However.... when you do that - you are FULLY committed to not going back.  So that is another major consideration.


Just some thoughts to consider.




One option to maintain your top-down design structure is to use skeletons. You could put the references from your master model into a skeleton and use that as a reference for your parts. To maintain your skeleton's independence, you can copy references and then break the dependencies. I recommend the collapse command for this. This method is top-down and allows for more simple reference management.


An alternate method might be to use a merge/inheritance feature to copy your master model into each of the parts that need to reference it. With this method, you can control the dependency of the part to the master model. If you want to break the links, you can choose the "no dependency" option.


As a side note, we design using top-down methodology and external references inside our Windchill environment. The dependencies are not broken at any point during the design process unless necessary. This can make certain things more difficult to manage but if you're careful about how you create references, it works just the same. We do enforce the use of skeletons, control the external reference scope, and create logical breakpoints in the design where reference sharing starts/stops.





21-Topaz II

Top down design tools by design create external references. Some tools allow for the reference to be made indpendent but not toggled back on.


Without specific knowledge of your PDM release scheme and vault and what tools are used to archive the data it is hard to speak specifically. When you need to uprev a part do you extract the model from your PDM system or from Windchill? I am assuming that you are using something other than Windchill as an archive for 3D CAD models with the comments below.


Have you considered saving a copy of the model with all features set to read only? This will prevent Creo from looking for external refs when retrieved. You can clear the read only setting and external refs will be functional. So anyone opening a model would not need to have any external references in session to open the model.


You can archive a Creo neutral or STEP file in PDM system. This will also not have external references. This would work unless you extract from PDM the Creo model for revisions. Some companies do this to protect the design data within the native Creo files.

Involute Development, LLC
Consulting Engineers
Specialists in Creo Parametric
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