assembly structure

[matt]

How do you set up your assembly/subassembly structure?

- subassemblies are stocked part numbers
- subassemblies allow efficient use of mates
- assembly structured to allow motion in the assembly
- assembly/subassembly structure according to the mfg/assy BOM document
- structured to create assembly instructions document
- all at one top level (no subassemblies)
- subassemblies structured to split up the CAD work (1 user = 1 subassembly)

or some other way?

[mike miller]

We usually base it on manufacturing processes, although we sometimes add another level for reducing mate complexity. The hierarchy usually resembles this:

Final assembly (as shipped)
Stage 2 assembly [optional]
Stage 1 assembly
Pre-assembly of components
As welded
Parts (weldments, machined, purchased)

Sometimes we have other simplified assemblies for testing motion or controlling in-context relations.

[MJuric]

How do you set up your assembly/subassembly structure?

- subassemblies are stocked part numbers
- subassemblies allow efficient use of mates
- assembly structured to allow motion in the assembly
- assembly/subassembly structure according to the mfg/assy BOM document
- structured to create assembly instructions document
- all at one top level (no subassemblies)
- subassemblies structured to split up the CAD work (1 user = 1 subassembly)

or some other way?

All of the above and then some depending on product, design type, resources available blah, blah, blah.

As with all things CAD I do not believe there is a "One size fits all" approach. If you're designing a basic fixture as a one man show the most effective and effecient approach is not going to be the same as if you're designing an airplane with 1000 other people which is not going to be the same as if you're designing the equipment to make the wing spar of that plane with 10 other people.

At one time or another I have used all of the approaches above.

-S/A's as stocked part numbers - We have a product here that uses an assembly that we stock as the base for other products.

-S/A Efficient use of mates - I think this is merely a factor in some of the other decisions. At some point an assy becomes unwieldy and breaking down for better mating, smaller size, usability, design resources etc becomes necessary.

S/A for motion - If you're designing a machine that has 50 axii...axis's...whatever...you're going to have to check for clearances, motions, travels etc. Assemblies designed around those motions become imperative for ease and effectiveness. Designing in such a way that does not allow this essentially means you have limited ability to check function.

S/A for BOM - I see this as kind of a chicken or the egg issue. Typically the design is completed before part numbers are applied so S/A become a part number on the BOM. Typically those S/A are dictated by other factors mentioned here. For family of parts it's then typically to follow the same format so then this becomes "the norm". For us it's "Spindle assy", "Guarding assy", "Base assembly" and so on. We often look at the machine and break it into these S/A's before we even begin the design.

S/A all at top level - I used to do a whole lot of Automotive gages. Almost never had S/A save imported library items like a "Go"/"No-Go" handles. If the entire assembly is only 20-30 parts then making S/A's becomes not only unnessary but in many cases it adds time, difficultly and complexity that is not needed or helpful.

S/A to split up work - When you have large design projects this is often the easiest method to work concurrantly. Again as an example here we have a top level assy that no one checks out unless they are adding, changing etc the top level. S/A's are typically assigned to another person. Even those S/A are typically broken down further so the "Spindle assy" might be "Auto tool", "Feed", "Spindle", "Spindle drive". You might have 4-5 people working on the spindle assy and so on. The larger the product the more sub divided.

[Glenn Schroeder]

I have very few top level assemblies that don't have sub-assemblies, and for me it's a combination of mate efficiency and detailing. For example, if I'm working on a bridge deck with a steel parapet rail, the concrete and rebar will be all one sub-assembly. That makes it easy to detail that portion in the drawing.

Then each steel post with it's hardware will be one sub-assembly, which is inserted into a higher level sub-assembly and patterned at whatever the post spacing is for that installation. I add the rails to this sub-assembly also, and then the top level assembly will contain only the two sub-assemblies; one with the concrete and rebar and the other with the posts and rails.

We only have two users here, and we usually don't work on the same projects, and never at the same time, so that isn't an issue.

[Frederick_Law]

Any combination of all.
Folder can work as temp sub-assembly.

[CarrieIves]

It depends on the size of my assembly and logical breaks. I usually have subassemblies lined up with manufacturing steps. The fewer subassemblies, the fewer drawings I have to create. BUT, sometimes it is a lot easier to make a drawing of a subassembly than to create the display state and explode steps in the top level than to have created the subassembly. Sheetmetal parts that get hardware added each get their own subassembly. I then create a drawing of the sheetmetal assembly rather than the part because I am going to order the sheetmetal assembly.

Lately, I've been doing small electronic assemblies with a couple of circuit boards with a couple of plastic parts holding them. That doesn't need to be broken into a bunch of subassemblies. Some of the designs I have worked on in the past had large enclosures with panels that get mounted to weldments and then electronics inside. Those had a lot more sub-assemblies. The subassemblies also can help with having more than one person work at a time,

Also, there is the assembly built up until it is functional vs. that with the box, manual, power cord, etc. I've created assemblies just to add the box level items, and sometimes, that can be controlled outside of CAD with just a BOM.

[bnemec]

Well, we were nearly 1 for 1 with manufacturing BOMs so sub assemblies each had a dumb "smart" number; in other words, it wasn't up to us. Recently some forces came to drive a change that is making a hash of what our subassembly structures looked like. There is no way we can keep up with the changes made to how the components are put together in the various work stations. So we will keep with what I've been calling "atomic parts": piece parts, purchased assemblies and weldments. After that its becoming a hash soup as the MBOMs are mutating. Then the top level model and drawing that goes to customer will of course match the "catalog" numbers but the BOM structure will likely not match.
We don't know if we change what we've been doing now that our assembly structure is not controlled by the manufacturing BOM structure or start something new.

- both the EBOMs (cad sub-assembly structure) and the MBOMs have had kits as we call them that have dumb "smart" part numbers, but are not stocked. Those are handy as the same set of parts and attaching hardware may be used in a hundred upper level assemblies, so it's much simpler to bring them in as a kit each time then individuals. Also simpler to maintain that way.
- All of our weldments are assembly files, no weldment part files.
- I'd guess about 90% of our non-weldment assemblies have some kind of motion, adjusting rails, risers, suspensions, etc. so flexible assemblies.
- have never set up sub assemblies by user or group
- all of our assemblies (except some purchased assemblies) use mates between geometry and part models are kind of centered about the origin, as opposed to locking all the origins in the assembly and positioning the solid body in the part model.

[Lapuo]

One assembly (part) for each part number.

For example :

sheet metal part = partnumber1
pressed part = partnumber 2 (assembly)
powdercoated part = partnumber 3 (assembly of assembly)
Welded assy = assembly of assemblies of assemblies

A lot of assembly in assembly here

Yes it is nightmare to track revision levels

[Ömür Tokman]

I do not work with large and complex models.
So it consists mostly of parts one assembly, I rarely use subassemblies for orders with a large number of parts.
I usually draw the parts with their rough outlines and create the assembly, then edit the part details in the assembly. There is no particular reason, I am used to this method and I think that I am fast this way.

[zwei]

Personally, i like to keep the structure same as the the manufacturing process
If necessary, we will further breakdown the assembly into some sort of dummy/phantom assembly (no one like to work on assembly drawing with 100+ item in the bom)

[Ry-guy]

How do you set up your assembly/subassembly structure?

- subassemblies are stocked part numbers
- subassemblies allow efficient use of mates
- assembly structured to allow motion in the assembly
- assembly/subassembly structure according to the mfg/assy BOM document
- structured to create assembly instructions document
- all at one top level (no subassemblies)
- subassemblies structured to split up the CAD work (1 user = 1 subassembly)

or some other way?

Oh, that's a great question!
I will see your question and raise you!

There are many different ways to represent your design and/or product. If your company is moving in the direction of a digital twin what type of BOM are you building?
How do you define a "finished good"? Is it the product or is it the product + shipping/packaging/instructions, etc.?
Does your PDM/PLM structure allow for a "model" (revision controlled) and then have all your finished goods related to the model?
Do you design using an eBOM or mBOM or sBOM? (e=engineering, m=manufacturing, s=service)?

[HerrTick]

Not a popular position, but...

Design structure should be separate from manufacturing structure. The manufacturing assembly should be an entirely separate assembly from the design layout.

Consider also tangential assemblies like service kits. These are usually a collection of parts without design context.

[MJuric]

Not a popular position, but...

Design structure should be separate from manufacturing structure. The manufacturing assembly should be an entirely separate assembly from the design layout.

Consider also tangential assemblies like service kits. These are usually a collection of parts without design context.

I've mentioned this before but all to often engineering gets drug down the road of "Designing for manufacturing", "Designing for sales", "Designing for quality" and on and on.

Other than consideration of cost and methods in all these areas design should be designed for function, compromising function to "make it easier" for any of these areas especially when that "Ease" compromises function and has minor effect on ease, is ludicrous.

[Glenn Schroeder]

I've mentioned this before but all to often engineering gets drug down the road of "Designing for manufacturing", "Designing for sales", "Designing for quality" and on and on.

Other than consideration of cost and methods in all these areas design should be designed for function, compromising function to "make it easier" for any of these areas especially when that "Ease" compromises function and has minor effect on ease, is ludicrous.

I was once involved in a project for a roadside barrier in a specific location in another state, and making it easy to keep it looking nice for the maintenance department seemed to be the driving factor. That was fun.

[bnemec]

Not a popular position, but...

Design structure should be separate from manufacturing structure. The manufacturing assembly should be an entirely separate assembly from the design layout.

Consider also tangential assemblies like service kits. These are usually a collection of parts without design context.

Ok, but how does that help if Design group now needs to maintain two sets of assemblies? We can hardly keep up maintaining the structure that matched manufacturing BOMS. Actually, with the latest change outside our walls, we are no longer keeping our assembly structure matching. So there will not be assembly that matches MFG BOM for many part numbers.

I don't think there is a one size fits all that structure planning that can be applied to all places that use 3d CAD.

[MJuric]

I was once involved in a project for a roadside barrier in a specific location in another state, and making it easy to keep it looking nice for the maintenance department seemed to be the driving factor. That was fun.

Exactly, a "road side barrier" that is easy to maintain but is not longer a barrier doesn't make much sense.

I've seen things like this done lots of times under the "It's to hard too..." design. What good is a completely compromised design that is easy to make and inspect?

That's not to say that all of these things that are brought up can't be part of the design process, it's just that they shouldn't be the driving factor in the design and all to often it is.

[jcapriotti]

Not a popular position, but...

Design structure should be separate from manufacturing structure. The manufacturing assembly should be an entirely separate assembly from the design layout.

Consider also tangential assemblies like service kits. These are usually a collection of parts without design context.

We are going this route in Windchill. How do you reconcile assembly drawings. The EBOM on the drawing and in Windchill match the balloons/find numbers. When you restructure the EBOM to MBOM in WC, those line items change. Now the drawing no longer matches the MBOM.

Do you create a new assembly and drawing just for manufacturing to match the MBOM? This seems redundant when it's a 99% match.

[bnemec]

Not a popular position, but...

Design structure should be separate from manufacturing structure. The manufacturing assembly should be an entirely separate assembly from the design layout.

Consider also tangential assemblies like service kits. These are usually a collection of parts without design context.

along with @jcapriotti, we understand it's not a popular position, but sometimes we're forced into situations and then have to make them work. Keeping our assemblies in line with the shifting sands of the Manufacturing processes was tough. Now it's becoming impossible so we're faced with EBOM != MBOM so seriously wanting to hear more about how others are doing this.

[CarrieIves]

We are going this route in Windchill. How do you reconcile assembly drawings. The EBOM on the drawing and in Windchill match the balloons/find numbers. When you restructure the EBOM to MBOM in WC, those line items change. Now the drawing no longer matches the MBOM.

Do you create a new assembly and drawing just for manufacturing to match the MBOM? This seems redundant when it's a 99% match.

I have worked places where the item numbers on the BOM in the PLM system were supposed to match the balloons on the drawing. We always had a lot of work to keep those lined up (I think we took the BOM off the drawings at one time). We finally settled on putting the BOM on the drawing with a note about it being for reference and the controlling BOM was the PLM one. It wasn't great, but it was a lot nicer having at least a reference BOM on the drawing.

[jcapriotti]

This is an example BOM mockup. EBOM from engineering. Manufacturing wants to add packaging materials and then combine the "Exit Sensor" and some fasteners into a kit.

Now the drawing engineering created does not match manufacturing. Not sure what the best solution for this would be. This is a simple example as well, the MBOM can really look a bit different.

[MJuric]

This is an example BOM mockup. EBOM from engineering. Manufacturing wants to add packaging materials and then combine the "Exit Sensor" and some fasteners into a kit.

Now the drawing engineering created does not match manufacturing. Not sure what the best solution for this would be. This is a simple example as well, the MBOM can really look a bit different.

Have no idea if it works for you but why isn't the EBOM an item on the MBOM. From an outside view it looks like the engineering is released. Item is manufactured etc. Then Shipping etc wants to add items to it for shipping. So it's the EBOM plus the other stuff.

I'm not entirely sure how other companies do this, but most of the places I've worked if it's part of the job, whether it's shipping, electrical, mechanical or anything else it goes on the BOM. Typically these are broken up into sub levels with a top level. So for us we have an electrical BOM, mechanical BOM, Shipping/Packaging BOM etc etc etc. So Mechanical may be considered an EBOM, but that is only a level of the top level which contains all of the other BOMS.

What that allows is for shipping to have a BOM that Engineering never sees and never has to worry about, but it shows up in the ERP/MRP even if no drawings exist of it.

[jcapriotti]

EBOM -Engineering BOM
MBOM - Manufacturing BOM

Manufacturing wants to kits some items and add shipping materials. They can even move some items completely out of the BOM and into another BOM based on how the components need to be put together in our factory and shipped.

[DanPihlaja]

I generally do it as if it were being manufactured. Anything that you put together first, then set aside to build a different area, is a sub assembly.

Example:
A plate has 4 dowels pressed into it, then is mounted to a sub plate.

So, a subassembly will be the plate and the 4 dowels, then the higher level is the 2 plates with the dowels and any fasteners involved.

[Ry-guy]

EBOM -Engineering BOM
MBOM - Manufacturing BOM

Manufacturing wants to kits some items and add shipping materials. They can even move some items completely out of the BOM and into another BOM based on how the components need to be put together in our factory and shipped.

Jason-
Are you using CAD to manage the MBOM? Or do you use a PLM to manage the MBOM? That's where I think a lot of organizations get things wrong- using CAD for MBOMs. MBOMs are different! They have a different structure, they serve a different purpose. eBOM describes what is built. MBOM describes how it is built and what was shipped. SBOM describes what your customer owns at a point in time.
Managing all these bom types is tough and really require a process that is robust enough to be able to pull data from multiple silos of information (PDM/CAD, PLM, ERP, MES, CRM, etc.)

[jcapriotti]

Jason-
Are you using CAD to manage the MBOM? Or do you use a PLM to manage the MBOM? That's where I think a lot of organizations get things wrong- using CAD for MBOMs. MBOMs are different! They have a different structure, they serve a different purpose. eBOM describes what is built. MBOM describes how it is built and what was shipped. SBOM describes what your customer owns at a point in time.
Managing all these bom types is tough and really require a process that is robust enough to be able to pull data from multiple silos of information (PDM/CAD, PLM, ERP, MES, CRM, etc.)

PLM mostly (Windchill's BOM transformation tool). We create a second "appending" drawing that shows mfg specific notes and the MBOM and maybe a view or two if needed. But we sometimes create a second, nearly duplicate assembly, if the changes are big enough so we can show different drawing views to show the differences. You need both the Engineering drawing and Manufacturing drawing to get the whole picture from manufacturing's perspective.