Part revision levels on assembly drawings ? 2

[shoelace]

This is a debate I have had at few companies I've worked.

On assembly drawings - on the bill of materials list - should one include revision level.

I believe - no. Revision level is a property of the part and should not be on the assembly drawing. It would mean that even the slightest change to a bracket would require a new assemply drawing revision.

Is that what configuation management is about. Recording the history of part revisions making up a given assembly?

The argument for putting part revision levels on assembly drawings is to record how a product went out the door at any given time in terms of part revisions.

Any thoughts on this issue ?

 

[aamoroso]

It depends on how well you control Part revisions.

Sounds to me like you don't use an ECN system for drawing control so:

If you revise parts when form fit or function changes you should include revs on the assy and probably have to in most instances.

If you revise parts for trivial crap that does not touch form fit or function then the rev of the parts should have not matter on the assembly.

In most well run systems a part number recieves a new part number when form fit or function change, which would possibly change the assembly if the new part number is going to replace the old, but if it is not in all assemblies then the obivous choice is to revise the necessary assemblies only and the older parts would still be used.


Another thing to consider is the scope of the assembly drawings, if it is for visual reference only with no directions on assembly or dimensions then it is not so important to rev the assembly.

All that aside, it really boils down to what works for you. I feel there is more control and traceability on an assy drawing with part revs, now if I could just convince my boss of that. Hey want to trade boss'.

Fill what's empty. Empty what's full. And scratch where it itches.

 

[shoelace]

aamoroso,

We only give parts revisions if the change is small enough so the new version of the part could be swapped with an old version on any old product. Otherwise a new part number is taken out and the old part is removed from the assembly drawing and the new one added - which, of course, would require a new revision to the assembly.

My feelings are that the revision of a part is a property of that part like material or surface finish is a property of a part and, hence, should only be recorded on the part drawing ... in the same way you wouldn't specify part material or paint finish on the assembly - so, too, you don't show revision level. Its true that you still need to record how products go out the door ... I just don't think that the assembly drawing is the appropriate place to record such information. To me, assembly drawings are for the guys on the floor ... instructions on how to build it. If it specified a bracket, they should not need to know whether it is rev A or B. They just pick up the part they are given and put them together as per the instructions. The process and ECN system should ensure that he gets the right revision of the bracket.

Sure, I'll happily trade bosses with you.

 

[aamoroso]

Consider this:

If an assembly fails at the customer or end user can you tell what version of the assembly they recieved. For instance if a revised component was the failure can you identify which customer recieved which version of the assembly. The component becomes a property of the assembly and when the property of the component changes (material grade for instance) it does change the properties of the assembly.

Much depends on your systems and products. How do you trace failures is a big issue where I work, parts change often and if one fails in an assy it is crucial we identify what other customers may be using a defective product. Without identifying the rev of the parts it is much harder to figure that out.

Logistically speaking will the cost of the labor involved outway the costs of not having rev control? If the boss says we need to spend the time and money to control product better then there is the answer.

Fill what's empty. Empty what's full. And scratch where it itches.

 

[ewh]

Most of the places I have worked at solved this problem through the use of serial numbers. The documentation shows what revisions went into each assembly.

 

[swertel]

Revisions do not control configuration management! If you are changing form, fit, or function, then a new part number must be created - even if only a dash number on the same base number.

If something fails at the customer, you know what part number failed. It is the same partner used elsewhere. The revision is inconsequential because a Rev A part always meets form, fit, and function of a Rev B part, or a Rev C, etc.

And to reiterate ewh, your quality control system that applied lot numbers and/or serial numbers to the components should give you your traceability. Creating a Product Baseline is another approach. But do not put the revision of a part on an assembly.

--Scott

For some pleasure reading, try FAQ731-376

 

[shoelace]

Some thoughts

When you assemble a product, you always want to use the latest revision of all parts making up that assembly. Exceptions are when you have old stock on the shelves. In this case you may choose to rework or use up this stock. The ECN system should specify what is to be done with old revision stock. Seeing part revisions on assembly drawings is only about recording history ... there is no other value. There would never be an instance where you would prefer to assembly a product with old revision parts. I just think you should record history elsewhere.

It is incredably irritating when you change a paint finish or add a chamfer on a small bracket and then must make a revision on an assembly drawing with 200 parts. Especially if the drawing contains many pages. So for every stupid little thing you change you have to muck around with a huge assembly. The job becomes 5 times longer than is required and your assembly drawing goes from A to Z in a couple of weeks.

I think that the MRP system should record history. Only it knows what is on the selves and what was actually taken out of stock when and for what assembly. I think that part revision levels on assembly drawing actually causes a lot more confusion and slows things down than any resulting value. Its a mistake waiting to happen.

Its a great make-work scheme however - because man, does it ever waste a lot of time.

Aamoroso, what is your bosses justification for not putting part revision levels on assembly drawings ?

 

[shoelace]

swertel,

Ok, now I see what you are saying ... and you are absolutely right. We have been changing revision levels when we really should have been creating new parts to replace old ones. By the form, fit, function requirement, you really can't change a heck of a lot before you need to create a new part to replace an old. Even changing material would affect function and would hence require a new part.... or changing plate thickness on a bracket would require a new part number ... which is a bit of a drag ... so many new parts all the time ... so many changes to the bills of materials ... so many more parts for stores to deal with.

But, I can't see an acceptable alternative if you really want to control your product.

I look forward to reading anything else you want to add to this discussion.

Aamoroso, by the sound of things, you guys should be changing part numbers more frequently as well ... rather than upping the revision level.

 

[shoelace]

Interesting article somewhat related:

http://www.dmsms.org/file.jsp?storename=Form_Fit___Function_Fundamentals.pdf

 

[aamoroso]

Yeah my problem is our boss is trying to force the rev levels into the part numbers. Which is just as big a nightmare as putting them on the drawing. We have been fighting for an ECN System but managemant cringes at the idea. With a good ECN system all the problems with revisions go away. Part numbering has been a problem in this company, the front office is driving engineering policies, it's like a volcano getting ready blow over the top. They keep trying to come up with these solutions in the front office rather than listen to the experienced engineers that have been through this all before.

Fill what's empty. Empty what's full. And scratch where it itches.

 

[swertel]

The article that shoelace posted is quite helpful and basically elaborates on what I was going to sum up. Change in form, fit, or function is based on the user, not on any specific definition. That being the case, how do you know when a change to form, fit, or function - by definition, requires a new part number to maintain configuration management. The answer is simple, rather the question is.

Is the new part COMPLETELY interchangeable with the original?

If you can answer yes to this question, then you can revise the drawing without making a new dash number or part number. Be warned, interchangeability is affected through all levels of the company, not just engineering and manufacturing. As mentioned above, if a part fails at the customer and one part was plated and the other wasn't, for example. Could the plating, or lack of, be a cause or catalyst to the failure? If so, you need to track that change with a new part number.

--Scott

For some pleasure reading, try FAQ731-376

 

[shoelace]

Here's anouther great link on the subject I found:

http://www.npd-solutions.com/configmgt.html

The website looks like a really good resource in general.

 

[Lyon1]

You should include the revision level on the assembly drawing. If you use a Product Data Management system, the revision level of the assembly should be part of the metadata collected for the part. It should also be imbedded in the design file(s) for the part. This practice assures that you will always be using the latest approved revision for your assembly.

The revision level should not, however, be marked on the physical part itself*. The part number itself should be modified (re-identified) if you have a Major (Class 1) change (non-interchangeability rule), and the old parts should be purged from all delivered assemblies and from your inventory.

* The exception here is on prototype parts and assemblies during the development phase (prior to the Product Baseline being established), when you may be making many changes to the designs and to the parts and you want to be able to keep track of both your design and the prototype parts and assemblies.

Hope this helps.

Dave Lyon
Raven Publishing Company

http://www.configuration.org

 

[ctopher]

ALL documents need a revision... parts, assy's, etc.
Sometimes you may have a part used several times on different assys and if it's rev updates the assys updates. It is the only way to have control.

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

 

[wes616]

In an Assembly Drawing, you enter the Part or Identifying Number (PIN).

According to Global Engineering's DRM (in accordance with ASME Y14.100 - 2000)

PART IDENTIFYING NUMBERS CONSIST OF LETTERS, NUMBERS OR COMBINATIONS OF LETTERSN AND NUMBERS, WHICH MAY OR MAY NOT BE SEPARATED BY DASHES OR SLASHES THAT ARE ASSIGNED TO UNIQUELY IDENTIFY A SPECIFIC ITEM. THE PIN SHALL BE OR SHALL INCLUDE THE DESIGN ACTIVITY DRAWING NUMBER AND MAY INCLUDE A SUFFIX IDENTIFIER (FORMERLY DASH NUMBER) IF APPLICABLE. THE PIN DOES NOT INCLUDE THE DRAWING REVISION IDENTIFIER, DRAWING SIZE OR ACTIVITY IDENTIFICATION.

Wes C.