BOM and assembly model organization

[bxbzq]

Hi there,
I recently have to make a choice of the BOM organization. Our product has several modules. Each of these modules has certain functions to serve the end product. During assembly, we actually take components out of modules and assemble them one by one. So these modules are not assembled as single whole pieces to make end product. When it comes to BOM organization, one way is the BOM is organized so that the manufacturing can read the assembly process/sequence and create their process documents. It is process oriented. The other way is to organize the BOM to reflect functional relationship of these modules. It is function oriented. I lean towards the first approach, but I'd like to know what others think.
It is also the choice I have to make for assembly CAD models.
Any help?

 

[KENAT]

bxbzq,

Engineering drawings (at least to ASME) generally defines the end item and sets out it's requirements.

Engineering drawings do not normally give process information - unless the process materially affects end function.

Engineering drawings do not necessarily have to match the structure of the BOM in your ERP system.

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[bxbzq]

KENAT,
So would you agree a BOM should be process oriented?

 

[drawoh]

bxbzq,

One of my design assumptions is that if I can document and model workable assembly instructions in CAD, the final system will be easy to assemble, and there is a good chance production will follow my instructions. If you are running 3D[ ]CAD like SolidWorks, the BOM is driven by your assembly model.

If a sub-assembly has to be installed in a final assembly piece by piece, it is not a sub-assembly. There should not be a separate assembly drawing and BOM. If your sub-assemblies are real sub-assemblies, production can have a worker build them and return them to the warehouse shelf. They don't have to do this, but they have the option. This could be a good idea if assembly of it requires some specific skill, or if the parts are delicate and safer contained within the sub-assembly.

If my assembly has function sub-systems that I cannot document as sub-assemblies, I create an arrangement drawing separate from the assembly that shows off that functionality. My assembly drawings show how to put it together, and they generate a functional BOM. As the designer, you are responsible for ensuring the thing is easy to assemble. Generating assembly instructions, is a good way to ensure this.

I have had one experience with an assembly with sub-assemblies that could not be assembled outside the main system. It was not designed by me. As far as I am concerned, the thing was shoddily designed. A proper, modular assembly wss totally feasible.

--
JHG

 

[KENAT]

Mostly agree with drawoh.

To your specific point I prefer the ERP BOM to be based on my Parts List which is part of my drawing so driven by function. But arguably what goes in ERP is mostly a production issue (at least for my employer - may not be quite so true in highly regulated industry).

When I set up my assy levels it's up to me to ensure they make sense in ways drawoh details.

"production can have a worker build them and return them to the warehouse shelf. They don't have to do this, but they have the option"

Sadly, the way our ERP is implemented they do have to put them back to stock - don't try telling them the ERP system is set up wrong.

So, they prefer 'flat' BOMS with few assembly levels, which means the assemblies get big and bulky to document, so instead of getting away with just several simple quick to produce assy drawings you need a lengthy and detail assembly work instruction...

So they get their flat structure, at the expense of a lot more time on documentation (which never seems to be updated and/or quite right) which for low volume stuff like ours I struggle to see makes sense.

Sorry, rant over.

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