Modeling & Documentation Trade-offs

[MadMango]

I wanted to drum up some discussion about the various types of trade-offs we are experiencing when it comes to building top-level models and providing 2D drawings for documentation. Now, when I say documentation, I mean drawings that are generated for several purposes. Some of these purposes might be:

Fabrication (forming, machining, welding, etc.)
Assembly (building sub-assys, constructing assys)
Presentations (eng. meetings, sales & marketing use, etc)

Many times, assemblies are mated during the design phase of a project to help the design process. Once that is complete, assemblies are mated to reflect the actual assembly method (at least at my company). This may require us to dissolve previous groupings of parts to create entirely new ones. This makes older drawings based on these now defunct assemblies have nice empty drawing views. And sometimes, configurations just don’t do the job, and entirely different assemblies are made.

Are others experiencing this same situation? What are your methods of getting around them? Maybe I'm just frustrated this week... is it Friday yet?



MadMango
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[TateJ]

While in the design process, I generally treat drawings as a tool for checking the design - and try not to invest too much time in a design drawing.
So, when I delete it - I haven't really lost much.
Then the fabrication drawing(s) will be my final check.
Also, I try not to use in-context features in an assembly part unless I know I'm going to replace them with real constraints in the final design.
This would not apply if I'm making a model to use in a submittal drawing - it's mostly smoke and mirrors anyway. And is not referenced outside a given project.
Is this the kind of feed-back you're looking for?

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[Standing]

MadMango,
If you are using PDM/Works you can open from the PDM Vault "as built" condition. Using the revision you had before the dissolved assemblies and drawings.

Bradley

 

[automationbabe]

We don't make assembly level drawings until the design is final. We use the model for our presentations. Fabrication drawings are done first, as a sanity check, to see if the part is machinable. Adjust our assembly model as needed, create real-world mates (actual assembly method)and then create the assembly drawing. Seems to work well for us. By then, the part details are pretty final, and the assembly drawing goes together easy.

 

[Arlin]

Isn't there some module or package that can help document manufacturing/assembly process that can differ from the SWX model? Similar to PTC's Pro/Process, I think.

This would allow manufacturing and assembly processes to differ from the SWX assembly structure, and yet maintain some sort of associativity to the SWX model.

I could be full of hot air, though.

At my previous job, we were always fighting with manufacturing about subassemblies. The engineers wanted lots of subassemblies to both incerase CAD performance and just make the whole product easier to manage (it was entire self-propelled machine). Manufacturing and assembly, however, wanted to see ALL assembly components in ONE BIG ASSEMBLY with no subassemblies, only weldments.

One method we used to get around that was through our MRP system where we could set up "phantom" subassemblies. This caused all "phantomed" subassemblies to be automatically disolved into the parent assembly on the shop order. Thus, the shop order never called for the subassemblies, but only the piece parts. The only issue then was that drawings did not match the shop order and would cause some confusion.

 

[Adrian2]

Dear Arlin and all;

I agree with your method of using structured bills of material within your MRP system to satisfy both engineering and manufacturing concerns. I used a very similiar method when I worked for a cartoning equipment manufacturer. Our subassemblies were set up in the BOM as parts lists.

An individual engineer could pretty much design an entire cartoning machine by checking off existing parts lists on the structured bill. ie RH or LH frame, 6 foot or 12 foot, etc etc etc. Then create the special parts lists he needed to meet the customer requirements.

When came the time to print shop work orders, the MRP system blew down the netted requirements for all the piece parts. A where used inquiry would show where those requirements were coming from. The parts lists referenced the welded assemblies which were printed out as required when the work orders were distributed.

As for modelling, I tend to shy away from modelling large assemblies in-context only because it is supremely difficult to go back 6 months later and make revisions. Especially if another individual created the model. You have to be so careful about deleting and changing relations in an in-context assembly. If the method you used to put it together is fresh in your mind, it's fine but months down the road its often easier to rebuild the model from scratch than spend hours of frustration trying to accomodate a revision.

I much prefer to make assemblies the old way, piece by piece. Then check them for fit using 2D drawing views. They are much easier to work with months later when you are updating everything to as-built.

Best Regards

Adrian D.

 

[JNR]

We really have not hit up against this problem, as our assemblies are all flat (no subassemblies). Manufacturing does their own manufacturing instructions, but that's about it. Where there is a subassembly of sorts, it is treated as a part in our assemblies because an outside vendor makes it. But you have me thinking.... I have a long flight to UK this weekend for a design review and nothing to do for 16 hours or so. So if I come up with any bright ideas I'll post 'em when I get back.

3/4 of all the Spam produced goes to Hawaii - shame that's not true of SPAM also.......

 

[Arlin]

>>our assemblies are all flat (no subassemblies)

How large are your assemblies? For the very large assemblies I deal with, this just does not seem practical. Furthermore, lots of subassemblies make the drawing less cluttered and make the owner's manual easier to create (for me at least).

 

[TateJ]

As far as flat assemblies vs. sub-assemblies goes:
It should be a simple matter to - right before sending to manufacturing - copy the main assembly to a new file and dissolve the sub assemblies.
Sure, you might loose a few mates, but you're thru with the design by then.
Just FIX 'em all...

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[Arlin]

IIRC, you also loose component patterns when disolving a subassembly....

 

[JNR]

Ah, sorry for the confusion - I don't have a lot of time to devote to the news group, but I believe it is very valuable and important. So I am often in a rush when I post stuff.

We make overhead mounted, wide field of view, Head Up Guidance Systems (tm) for transport type aircraft (ie: not fighters). Our models certainly have multiple assembly levels and contain entire aircraft cockpit assemblies, tooling, our avionic systems, etc, etc. So we can run sometimes into 10 - 20k or more parts in a top level installation in order to design them to fit. But what we manufacture - just the avionics boxes and tooling themselves - have few levels of model assembly in them. Our manufacturing people want "flat" assembly DRAWINGS is what I meant. PCB assemblies are handled differently of course, but in the assembly drawing they are just one object as far as the single level BOM is concerned. They are fabricated outside, so on our manufacturing floor they are just another item to build into the assembly. So even with PCB's in the assembly, our BOM's rarely go to more than 3 levels. Even castings, machinings etc., almost everything is fabricated outside. Actually, manufacturing do build some things up in a subassembly method. But that is handled in their manufacturing instructions. Part of the reason is the FAA cert. process and how our repair center works with that. The same drawings work for both, with different manufacturing or repair instructions. Also we don't do BOM's in SW - they are handled in a completely different MRP system. All we do is glean the information and send someone a printout to input manually!!!!! That will change, but not for a while due to the cost. Eventually we will be on SAP like the rest of Rockwell Collins :-( ;-(

3/4 of all the Spam produced goes to Hawaii - shame that's not true of SPAM also.......