1 RFC/ECN, multiple revisions

[smcadman]

Let's say there are 2 revisions that need to be made in a sub-assembly on 2 different parts, should there be 2 top-level revision numbers or just one to reflect the part-level revisions? Hopefully that wasn't too confusing, so here is an example:

Scenario 1
Assembly Rev. B (notice Rev)
Part 1 Rev. A
Part 2 Rev. A

OR

Scenario 2
Assembly Rev. A (notice Rev)
Part 1 Rev. A
Part 2 Rev. A

I would believe that if Part 1 and Part 2 are on the same ECN/RFC, then the top-level revision should be Rev A, just tell them to see the affected ECN/RFC. Another here believes that for each part that is revised, the top level Rev should be the next consecutive Rev.

Note that this scenario is only if there are multiple revisions on the same day, at the same time. I know it would be different if a revision was made to a part, and later on another revision was made to another part.

Flores

 

[MintJulep]

None of the above.

Advance a drawing revision level when that drawing, and that drawing only, is changed. Period.

 

[TheTick]

It depends on how your assembly drawing BOM looks. If the BOM lists revisions, then the assembly drawing should change to reflect this. Also, if fit/function of assembly is dependent on component revs (regardless of whether component revs are mentioned in BOM), then the assembly drawing should be updated.

If multiple components change, the assembly is still revised only one level, so long as all revised components are noted as changed. The assembly is changing one time.

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[smcadman]

MintJulep, so are you saying you only put the revision on the part drawing, and do not put a revision on the assembly that is affected by that revision? Not that you are wrong, but I disagree with that practice. Our drawing packets can be anywhere from 5 sheets to 60 sheets. If a sub-level revision is made, then the top-level is revised to note that change. If Part 1 is revised, then the assemblies that have Part 1 within it are revised.

If multiple components change, the assembly is still revised only one level, so long as all revised components are noted as changed. The assembly is changing one time.

That's the way I am used to, but our QC believes otherwise. The BOM's do not have a Rev field in it, but our titleblocks do.


Flores

 

[MechCT]

I think that unless the two rev'd parts are changed in a way that modifies the form, fit, or function of the assembly or are changed in a way that they require retooling or alternate positioning within the parent assembly, that the revision of the assembly should stay the same.

Look at it this way... If you have a part that changes slightly (thus bumping the rev on that part) and it's used on 172 different assemblies are you going to go and rev each one of those assemblies? I wouldn't. Unless it was a major change that would affect how those assemblies were used or how other parts within those assemblies were used.

 

[MadMango]

I agree with MechCT on this.

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[ctopher]

Parts and assemblies are different, they have their own revs. Part dwgs and it's part have same revs, assy dwgs and it's assy have same rev.

Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP3.1 / PDMWorks 05
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

 

[smcadman]

MechCT, you have a good point. We use Solidworks, and PDMWorks is our PDM. I have had to check out 3 drawings in the past to update the assembly drawing revs. If we only had to rev the part, then every drawing that has that part would be revved and updated just by checking in that 1 single part.

I have brought that point up with QC in the past before; maybe I'll have to press that issue again.

Flores

 

[ctopher]

I agree with MechCT
No reason to rev an assy if a part changes, unless it is a notable design change shown in the assy.

Chris
Sr. Mechanical Designer, CAD
SolidWorks 05 SP3.1 / PDMWorks 05
ctopher's home site (updated 06-21-05)
FAQ559-1100
FAQ559-716

 

[cpdpeckh]

We have a rule that all non-interchangeable changes require a revision level change for the purpose of supply chain management.

Definitions:

Non-Interchangeable means for one reason or another (physical incompatibility, differences in performance or durability, internal differences in serviceable components, cosmetic appearance or simply for follow-up purposes) the revised and existing versions cannot be mixed and unique identification is required.

Interchangeable means that stock of the revised part can be mixed with existing stock of the same part and that either version can be used indiscriminately for production and/or service.

Are the top assemblies Interchangeable per the definition above?

 

[drawoh]

I agree with MintJulep and MechCT on this one. The rule written out explicitly in DOD-100 is that you do not revise a drawing to change form, fit or function. Any changes to the part require a new part number. You do not call up drawing revision numbers on the parts lists.

The consequence of this policy is that a revision correcting a spelling mistake on a fabrication drawing has no effect on the next assembly.

A change to form, fit and function affects the part number on the assembly drawing, and consequently, triggers a revision.

JHG

 

[smcadman]

It varies, some can be interchangeable, some cannot. For example, 1 tube will now use 3/8-16 nutsert instead of a 1/4-20 nutsert, so the hole in the tube has to be bigger. A stemmed caster screws inside the nutsert. That MAY be interchangeable because a smaller caster would work on the original assemblies, but a larger caster is now required (which has a larger stem).

On another part, a 14 ga. sheetmetal part flexed under weight, so we are bumping it up to 12 ga. Even though the part is interchangeable, because of liability issues we couldn't use the thinner gauge.

Flores

 

[wes616]

I am curious why someone would use a Rev in the bom on an assembly? It seems like a silly practice. I can see in some situation you would be switching from one version to another, but wouldn't you just stick with the "older" drawing until the new parts arrive.

One of our last product packages has something like 500+ sheets. Many of them share parts. I'd hate to "change" all those drawings, if one part "rev'd up"...



Wes C.
------------------------------
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[drawoh]

smcadman,

There was one other aspect to your question.

If I am making two unrelated changes to an assembly at the same time, I do one revision. It will call up both ECN/ECO/ECR numbers. My assumption is that no assemblies will be manufactured with one change and not the other.

This might be affected by the way your PLM software works, and there might be a company policy at your end.

JHG

 

[Kwan]

In my experience I've seen two different configuration control systems.

One is to carry a revision level to the part/assy. The revision level is tracked for each part. One can rev up a part (due to form, fit, function) and the assy would stay at the same rev level. The configuration of the assy is tracked thru the planning department. The engineer must disposition existing parts and their assy (ie: scrap rework, etc). A spelling type error would rev up the drawing sheet but the parts/assy does not change. This system is great for engineers because it cuts back on the paperwork.

The other system is one more widely used (my opinion). This system adds a dash number if a form, fit, function change is made. This forces the engineer to rev up the assy by making another assy dash number. This system causes more paperwork for the engineer, but it controls the configuration better (my opinion).

The big question is what is form, fit, function. This is a debatable subject for many part/assy changes. Perhaps someone can help shed some light on this?

Hopefully this makes sense.

 

[MintJulep]

Smcadman,

No, I'm saying that if a drawing changes, you advance its rev.

If a part drawing changes, advance its rev.

If the change to that part drawing forces a change in an assembly drawing, advance the assembly drawing's rev.

If two part drawings (of the same assembly) change, advance each drawings rev.

If the changes to those two parts force a change in their associated assembly drawing, advance the assembly drawing's rev by one. The assembly drawing only changed once.

Not all changes to a part force the assembly drawing to change. For example, a change of material or plating without any dimensional changes would likely not reqire an assembly drawing change (unless your BOM lists such details), as the change is essentially "invisible" to the assembly drawing's purpose in life - which is to show how to put things together.

A change of a part dimension most likely will force a change in the assembly drawing.