advice needed on revision control

[hobbs101]

Hi All

I'm a freelance engineer working on small design projects (typically <100 designed parts). Projects are generally industrial machines that sell in small numbers. With each sale of a machine, design improvements are made.

I'm looking to devise a simple revision control system. I use Autodesk Inventor. No PLM/MRP system.

I understand from other posts on this forum the rules on form/function/fit. For me that will generally mean that whenever I modify a part, it's part number will change. I'm happy with that.

I'm keen to have the part number the same as the (root) drawing number, i.e. if the part is P-100-12301, then the first released revision of the drawing will be P-100-12301-A. (I'm happy to reconsider this if it makes life a lot easier!).

I won't state drawing revision levels on sub-assy and GA drawings, as I understand this is not necessary as revision levels should be interchangeable.

So, when I modify a part that changes form/function/fit I change the part/drawing number. Does this then mean I need to update the BOM's on the sub-assy drawing and the GA? I guess if the part change changes the FFF of the sub-assy then that also needs to change assembly/drawing number, and so on.

Thanks.



Hobbs101
Mechanical Design Engineer

 

[swertel]

I agree, Kenat. There is some overhead associated with it. But, in my experience, no more than with any other change control process.

The main benefits are 1) human readable information, regardless if integrated into a PDM/PLM system, and 2) most PDM/PLM/ERP systems can easily be configured with naming and numbering rules that handle two insignificant sequential series concatenated into the unique ID.

--Scott
www.wertel.pro

 

[drawoh]

When changing part numbers, there are actually two things to consider.
The first, as you mentioned, is form/fit/function.
The second, which is often overlooked, is two-way traceability.

If there is a problem in the field, can my customer give me the part or model number (the item they actually purchased) and can I tell exactly which part at which revision went into the item?

...

If you are systematically not changing form, fit and function of your parts, then you do not care about the revision number. If you need new parts, you fabricate or build to the latest revision of the drawing. The revisions to the fabrication drawing are corrections of errors, clarification of instructions, or formatting of the drawing. I suppose that a non-functional modification affecting the cost of the part would be okay.

--
JHG

 

[MikeHalloran]

I suppose that a non-functional modification affecting the cost of the part would be okay.

It would, but sometimes non-functional modifications turn out to be, er, functional, or erroneous, so your production records really should tell you what, exactly, went into any given assembly/product, or you will be recalling products that are perfectly okay in order to correct the subset that are not.



Mike Halloran
Pembroke Pines, FL, USA

 

[ptruitt]

Designs are documents and parts are physical assets. Controlling complex designs is tough enough without trying to manage physical objects. Those responsible for mastering design control are usually not the same people who are responsible to controlling the physical assets. There are exceptions, of course. I usually urge people to read thick books, but I found a short internet article that resonated with me by searching "Life after Mil-STD-100: Decoupling part and document numbers". I recommend entirely separate document and part numbering schemes. Documents and parts should be linked in a database using effectivity dates establish by those who need to manage the change in production, in my opinion. By the way, I did not write the article or books I mentioned I have no business relationships with any of them.

Peter Truitt
Minnesota

 

[swertel]

Decoupling part and document numbers also adds the benefit of being able to model multiple representations of the same part.
Let's take a soft good like O-Rings as an example.

In my vendor item drawing, I'm going to model the O-Ring at nominal diameter and circularity. But everyone knows an o-ring at installation is squished or stretched. That means for every assembly that I install an o-ring, it will have to have a different representation. By decoupling the part number with the document number, I can cross-reference each of the representations of the o-ring with its original defining part number and document definition.

--Scott
www.wertel.pro

 

[KENAT]

Hang on, when we're talking part I'm thinking real hardware. Swertel seems like you're talking CAD Model. There are other ways to model multiple reps.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[ptruitt]

I'm the designer in the development phase of a design project, now, and have asked Purchasing to help get quotes. But Purchasing and Quality insist that part numbers be assigned, first. My CAD program auto-assigns document numbers and my CAD documents often include many non-interchangeable configurations during development. But their system cannot accept having more than one part number related to one document number and they don't want to refer to the design numbers. So here I sit waiting for someone to assign me some part numbers (six digits, no tabulations) while a co-worker splits my configured CAD models into single-configuration CAD models so the design can be approved. I'm convinced that our so-called ECO system is really a PCO system with a very, very weak relationship to design control. My design document numbers never appear on the ECO form even though the revision is driven by the design number which is always linked in conversations with the part number. I think I need to up my Prozac prescription... Not having a good week...

Peter Truitt
Minnesota

 

[swertel]

Not entirely, KENAT.

I was trying to make the relationship in the "digital thread." That which is modeled virtually compared to that which is purchased physically. When filenamining, part naming, and document naming get intertwined, there must be a way to cross-reference each of them. So, in my example, how can I 3D model an O-Ring in a unique configuration, give it a single identifying part number used by any number of other uniquely modeled configurations each with their own unique identification, that all point to a single document that provides the purchasing information for the O-Ring that has its own identification.

I believe this would get off-topic from the original question and should be started into another thread. But it is a very interesting predicament into document, part, and phantom IDs. Relating to the original topic, do I have to revise the document every time I create a new representation of the part?

--Scott
www.wertel.pro

 

[drawoh]

I'm the designer in the development phase of a design project, now, and have asked Purchasing to help get quotes. But Purchasing and Quality insist that part numbers be assigned, first. My CAD program auto-assigns document numbers and my CAD documents often include many non-interchangeable configurations during development. But their system cannot accept having more than one part number related to one document number and they don't want to refer to the design numbers. So here I sit waiting for someone to assign me some part numbers (six digits, no tabulations) while a co-worker splits my configured CAD models into single-configuration CAD models so the design can be approved. I'm convinced that our so-called ECO system is really a PCO system with a very, very weak relationship to design control. My design document numbers never appear on the ECO form even though the revision is driven by the design number which is always linked in conversations with the part number. I think I need to up my Prozac prescription... Not having a good week...

Peter,

When you design in 3D[&nbsp;]CAD, you need to account for how you will send information to purchasing and production. If you cannot tabulate drawings, you must not generate multiple functional configurations of your models. I am not allowed to tabulate at my site. I feel your pain.

I have had the experience of taking over a design project where someone attached multiple assembly drawings to configurations of one assembly model. This is an unsustainable mess. There is no reason to assume that the model attached to drawing[&nbsp;]A also affects drawings[&nbsp;]F and[&nbsp;]H.

--
JHG

 

[truckandbus]

How many common parts carry over from project to project? Sounds like it would be easier to create a new part number if you can't use an existing part 'as is'