Assembly Drawings consisting of a Bill of Materials only 1

[fogleghorn]

Our Director of Engineering wants to release Solid Edge Assembly Drawings with nothing more than a Bill of Materials on the drawing, no views at all. These "drawings" would then be turned over to Manufacturing Engineering to create Assembly Instructions. The thought behind this new process, would be that it would free up engineers much sooner to work on the next new product. Does anybody else release assembly drawings that are just a Bill of Materials?

 

[drawoh]

fogleghorn,

This sounds like an excellent strategy for making sure things cannot be put together.

A huge advantage of 3D CAD is that you can generate manufacturing documentation early in the design process. It will update as you change stuff. Meanwhile, everyone, including the designer, can evaluate fabrication and assembly procedures. If the documentation is someone else's job, that someone else will have to generate documentation that makes up for shoddy design.

It would be so nice if there was such a thing as a can of DFMA that you can spray on your CAD station at the completion of your design.

--
JHG

 

[CheckerHater]

The questions are: what industry you are in; how complicated the assemblies are, how much data your assembly drawings used to carry in the first place, etc.
If I understood correctly, your design engineers create 3D assembly models; they just leave it to manufacturing engineers to make exploded views out of them. You may get away with that.
I used to make assy dwgs with iso view, not even exploded; but they were intended for our own shop, so the guys could just walk in and ask “what’s that?”
Today, when design is actually done in 3D, importance of old-school layouts and assemblies diminishes; assembly drawings are often reduced to exploded views/ assembly instructions anyway.
So, if your bosses put the procedures in place to make sure no important data is missing in action, it doesn’t really matter who will prepare said exploded views.
It almost looks like a political problem rather than technical. It could be worse: they could put making assembly instructions on designers and get rid of manufacturing engineers altogether.

 

[fogleghorn]

We design and manufacture analytical instrumentation. The assemblies can be as small as a printed circuit board card cage with 4-8 mechanical components along with 3-5 printed circuit boards, or as large as 150 components that consist of sub-assemblies, fasteners, cables, fittings, brackets, etc. Our assembly drawings up until this point in time, have been exploded step-by-step assembly instructions.

 

[KENAT]

A classical assembly drawing per ASME Y14.24 (not a bunch of exploded views) really isn't that time consuming to produce in Solid Edge unless you have a really large assy or a lot of non graphic parts or a bunch of requirements that aren't conveyed by model geometry.

The auto balloon function means you can get a half assed one almost for free.

You're saying your Director doesn't even want to go to that much effort? In that case why bother with even a BOM drawing, why not just show them the assy model and tell them to get on with it?

I get the feeling we're missing a lot of the information we'd need to really answer this question as CH hints at.

I'm all for getting the 'how to' information off of the engineering drawing and leaving it up to manufacturing engineering to address.

However, the engineering drawing still needs to cover the 'what' as in defining the finished product and I don't see that just a parts list/BOM truely achieves this.

(There have been previous threads about what should go on an assy drawing and what should be in a separate travelor or assy work such as thread1103-157857 instruction etc. maybe take a look

http://www.eng-tips.com/search.cfm?...ng+&t=&h=&searchSite=1&searchArea=1&d=1&s=1.)

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[fogleghorn]

[If I understood correctly, your design engineers create 3D assembly models; they just leave it to manufacturing engineers to make exploded views out of them.]

Yes, the design engineers create the 3D models of components and create the 3D assemblies. The design engineers also create all of the exploded view assembly drawings/instructions. And yes, it is a political problem.

 

[KENAT]

fogleghorn you posted while I was typing.

"Our assembly drawings up until this point in time, have been exploded step-by-step assembly instructions."

Yes that can be time consuming and it's not unreasonable to propose that manufacturing engineering be required to do the detail assembly process part.

Take a look at ASME Y14.24 if you can - though it doesn't have as much detail & examples as might be liked. A classical assembly drawing per this standard shouldn't take as long to prepare as what you're currently doing.

However, a good assy drawing isnn't just a parts list - or even a parts list with token views. You need enough views to show where every item ends up. You also need to capture all other requirements/definition of the end item that define the finished item.

This doesn't mean the CAD data can't be used to generate the detailed assy procedure stuff though - and there are ways to directly use the 3D data for that.

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[fogleghorn]

KENAT, you are correct. I have left out some important information. Manufacturing Engineering is currently in the market for a draftsman/illustrator to produce step-by-step assembly instructions. Up until now, the manufacturing engineers reviewed the step-by-step assembly drawings/instructions that the design engineers produced, and either marked them up to be changed (usually requesting more detail) or sign them off if they thought that there was enough detail. The Director of Engineering has gotten frustrated with the fact that Manufacturing Engineering is so willing to spend engineering money producing assembly instructions. The higher-ups got tired of hearing all the bickering and said that Manufacturing Engineering needs to get a draftsman and produce their own assembly instructions, and engineering needs to determine what they are going to release as the controlled engineering assembly drawing.

 

[KENAT]

fogleghorn - we've had some of those arguments and in some ways still do.

I'd definitely suggest investigating the idea of Engineering releasing a classical engineering drawing in lieu of your current hybrid assembly drawing/work instructions.



(By the way your description of your employer sounds eerily like my employer.)

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[drawoh]

fogleghorn,

Think hard about your office politics.

I have worked at a site where engineering generated a stack of fabrication drawings for a product, then they handed to manufacturing. There were no assembly drawings and no parts lists.

Manufacturing eventually got the thing working. The process was not trivial. They wrote their own assembly procedures. They worked out what stuff MRP had to order and stock. Try to imagine the respect manufacturing has for engineering in a situation like this. Manufacturing took complete control of the product.

If you want to control the design, you must control all the drawings. If you want to control the drawings, you must meet everyone's requirements, including those of manufacturing.

--
JHG

 

[MikeHalloran]

At a former employer, we were forever changing our assembly drawings (of complicated mechanical/ electronic/ pneumatic/ fluid handling assemblies) to reflect changes in the manufacturing process, as the manufacturing operation built, stored and retrieved subassemblies on the way to final assembly. Restructuring the set of sub and final assembly drawings was incredibly expensive, and a huge waste of everyone's time.

JIT changed all that.

After JIT arrived, we didn't even have a BOM in the form of a final assembly drawing with no views. The product's BOM structure was reflected and recorded in the MRP system, only. You could get a BOM sliced and diced any way you wanted it, but it came from a line printer, not a drawing.

The assembly sequence was recorded in the Manufacturing Instructions, comprising detailed illustrations of what part came from which bin and went where in the assembly under construction at each JIT station.

I don't want to understate the cost of producing the first set of MIs. It took a team of specialists most of a year. It should be much easier now to pick them out of a 3D CAD system, but it's still a substantial investment.

The thing that was hard to accept at first was that the MIs were under the control of Manufacturing Engineering, not Design/Product Engineering. After we got over that shock, we were told that the 'master' MI for each sheet was the actual markup at the JIT station, and the reproducible versions in the office trailed behind them and were updated as time allowed. ... but process changes could happen instantly.

It all worked like a charm.


Mike Halloran
Pembroke Pines, FL, USA

 

[KENAT]

One thing that occurs to me, and perhaps relates to some of Mike's points is that the way Engineering records the design doesn't necessarily have to completely mesh with how manufacturing assembles it. Obviously at the top level end item there has to be correlation but in terms of how sub assemblies etc. are detailed not necessarily I suppose. This may mean that you have to think more carefully that part numbers do not necessarily match drawing numbers and various other aspects but it could be something to ponder.

I certainly appreciate what Mike says about having to update assy drawings every time manufacturing changes their process.

I'd also like to back up what drawoh says - if engineering no longer documents the assy process they need to be careful to still consider it when designing. While I don't enjoy doing it much I have found that creating the detailed assy work instructions get me thinking about the 'design for assembly' aspects.

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[drawoh]

One thing that occurs to me, and perhaps relates to some of Mike's points is that the way Engineering records the design doesn't necessarily have to completely mesh with how manufacturing assembles it...

I recently inherited a drawing package of a fairly complex system, all divided into sub-assemblies. My first impression was that the drawings were not very good or informative. When I got further into it, I realized that it was not possible to assemble the sub-assemblies, place them on a shelf, and later install them as is on the final assembly. The original designers ignored modularity. If this system had been passed on to a manufacturing organization such as the one MikeHalloran is describing, they would have had to reject the engineering documentation, and create their own system.

If engineering, as per DFMA, breaks the system down into separate modules, manufacturing has the option to build and warehouse the sub-assemblies, or to do the whole build, in sequence, on the one workbench. Either way, engineering's drawings are being followed. If engineering and MRP/ERP talk to each other, the engineering BOMs can be imported electronically into the database.

The fun starts when manufacturing concludes that the engineers are a bunch of idiots. There is no point talking to the engineers about design changes because they have no clue of what they are doing. Now let's review them weld specifications!

--
JHG

 

[KENAT]

I didn't mean to imply the way engineering documents it shouldn't be manufacturable. Just that if manufacturing later decide to merge assy levels in production as you say drawoh that doesn't necessarily mean drawings have to be changed.

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[MikeHalloran]

One cornerstone of JIT is that it's insane to make, store, and then retrieve subassemblies, because all the associated labor and space contributes nothing to the finished product. ... unless you are selling subassemblies.

DFMA does not require modularity; it only deals with the difficulty of assembly, for a module, or for an entire product, or for a particular JIT workstation's operations.

There are good reasons to make modules, but they don't all have to do with assembly sequence.

Example: I bought a replacement handle for my Ford van door. But dealers don't stock the handle. They stock a 'door kit', which includes every removable part for a given door. Which reduces the number of items a dealer has to handle and stock, and makes it unlikely that I'll walk away from the parts counter without handing the dealer $100 or more.

Similarly, for any product, you might want to group individual parts into kits for your service people or your dealers, reducing the number of Field Replaceable Units everyone has to document, handle, store, and deliver.

So a given product could have several BOMs, all structured differently, and several sets of MIs, depending on whether you are building final product or FRUs or something else.

Product engineers are not all-knowing about this stuff, though it is to their great benefit to understand it. Just don't assume that you know the best sequence of assembly, even if you designed the product; especially if you designed it.





Mike Halloran
Pembroke Pines, FL, USA

 

[ctopher]

It's not an assembly drawing if there is no assembly "drawing" on it. If he wants a BOM, call it a BOM, or PL, on a 8-1/2x11 sheet.
Engineering managers should have some experience with drawings to be an engineering manager.

Chris
SolidWorks 11
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[fogleghorn]

The mechanical engineering manager has been directing his department to produce a hybrid assembly/exploded view drawing for years. He is okay with producing a "classical assembly drawing per ASME Y14.24", and then letting manufacturing engineering create the assembly instructions with the new draftsman that they are getting. The mechanical engineering manager's biggest fear of creating a BOM only assembly drawing, is that the assembly instructions won't be completed in time for the initial production builds. In which case, the mechanical engineers will be down on the shop floor having to show the assemblers how to put the instrument together, instead of designing new products. The director of engineering (the mechanical engineering manager's boss), along with the electrical engineering manager are the guys pushing for BOM only assembly drawings from engineering. The director of engineering also serves as the software engineering manager (his background is software), so he has very little experience with DFMA, assembly drawings, etc.

 

[bxbzq]

Assembly drawings are not only intended to show the components assembled. For whatever reasons, there may be functional requirements (stack ups, eletrical, strenth) defined at sub-assy level, your sub-assy goes through test procedures to ensure the funcional requirements of finished product. That knowledge does not belong to mfg engineering, but to product engineering.

 

[truckandbus]

We had a similar edict given here - only problem was the M.E.'s weren't told they had the responsibility to create the shop floor level documentation so production wound up with no information from design and no information from m.e.

There was nothign wrong conceptually, just no process in place to make sure the work was done

 

[fogleghorn]

I guess you can make any process work, just so long as you document it and reach consensus from all concerned parties (in this case, engineering and manufacturing engineering).

The 3D Solid Edge Assembly Models along with the hybrid assembly/exploded drawings have worked for years. They have allowed us to manufacture, trouble-shoot, and service our products.

The hybrid assembly/exploded drawings are under ECO control, so there is only one document per assembly that needs to be maintained. I see that as a plus.

In our case, it usually takes an engineer along with a designer/draftsman a couple of weeks to create all of the hybrid assembly/exploded drawings for a new product. You may reduce this time in engineering to a couple of days by going to BOM only drawings from engineering that are under ECO control, and having manufacturing engineering create assembly instruction drawings that may or may not be under any sort of control. The question is... is it worth it?