Maintaining Tolerance stacks 2

[SDETERS]

What are some of the best ways to maintain your tolerance stacks of a project from start, and into production? For example when starting a project, tolerance stacks are done, but once the project goes into production for a couple years, things get modified, and updated, the tolerance stacks seem to go out of date over time.

 

[3DDave]

I bet few companies do anything. The best bet is something like VSA (Variation Systems Analysis) software that integrates the tolerancing analysis model into the CAD model so that dimension and tolerance value changes can be automatically updated and the tolerance reports rerun at whatever level one cares to. If the topology of the part changes then there would need to be some rebuilding; similarly to how stress analysis is done.

 

[ctopher]

Have some type of ECO (eng change order) system in place. Nothing changes unless approved.

ctopher, CSWP
SolidWorks '19
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[SDETERS]

We run NX and VSA is now integrated within NX now, VS the vismock up application. We have a standard spread sheet we use to track all of our tolerance stack with. It does a great job, it is just disconnected in the workflow, and also disconnected from the drawing also. So I was wondering if the VSA software would make things a little better, especially if we start to use 3D PMI on our 3D models, vs just having 2D drawings.
We have tried to put a tick in the ECO ECN form, but it does not get use often. Many different reason for getting missed.

Thanks do appreciate it.

 

[greenimi]

I bet few companies do anything. The best bet is something like VSA (Variation Systems Analysis) software that integrates the tolerancing analysis model into the CAD model so that dimension and tolerance value changes can be automatically updated and the tolerance reports rerun at whatever level one cares to. If the topology of the part changes then there would need to be some rebuilding; similarly to how stress analysis is done.

I agree. CeTol also integrates the analysis at the CAD model / assembly level.
Disclaimer: I am not working for Sigmetrix (CeTol)

 

[3DDave]

I've tried to get across that Dimensioning and tolerancing is a software development job, but the majority think it's a drafting job with trivial equations. In software development when a module is changed and "checked in" there can be automated processes kicked off to do a full build of the top level of the software to check for simple errors and to ensure all the parts link properly. More sophisticated development then runs known test cases. AFAIK no CAD/CAE software offers that as a typical workflow, including re-running stress analysis or tolerance analysis for the entire project, preferably only for those areas affected by the change. No EO/ECN or anything else required.

It is certain that no one manages to deal with the effect of acceptable variations on stress analysis. Sigh.

 

[Belanger]

The old-school way is to create a matrix that tracks each stack calculation and what parts or features it touches. If a dimension on that part or feature gets changed someday, use the matrix to see which stack-up calculations will be affected by that change.