In my work in the PLM world (ha! See what I did there?) I often hear that release must be bottom-up. But from what I’ve seen that is rarely what is actually done. In truth, release is usually done top-down. We say that components need to be released before the sub-assemblies they go into, and the sub-assemblies need to be released before the assemblies they go into. But that isn’t necessary. It is often not even desirable.
Releasing Parts Top-Down
Let’s say I’m designing an Airplane. I know the airplane has two jet engines. I know the engines have a turbine. But if it’s early in the design cycle I probably don’t know how many turbine blades will be in the turbine. Regardless, Purchasing wants a bill of material released so they can start the process of ordering parts and material. I cannot hold up the release of the engine until the design is completely finished. For an initial release of the BOM it’s enough to say that the airplane has two engines but the details will be finalized later.
Releasing CAD Designs Top-Down
Later in the design cycle I need to develop an assembly drawing of the engine. For my drawing I need to show how the fan and the compressor and the turbines and the nozzle all go together. But I really don’t need every detail of the contents of each sub-assembly fully defined. For an assembly drawing I only need the exterior dimensions and interface. So my CAD design may still be a work in progress.
Releasing vs. Freezing
What may confuse people is that what we don’t want is for the CAD design used for the drawing to be modifiable. We want a static representation of the turbine, even if it isn’t completely correct yet. Therefore we generally insist that the components go through some sort of process where they are made read-only before the assembly can be released. We might call it
releasing the components, but it probably doesn’t involve a formal or full review process — if it did, that would be significant delay in the schedule. Would you really want to hold up release of a top level assembly drawing because some bracket four levels down wasn’t released yet?
We don’t really need bottom-up release. What we want is a bottom-up freezing of the CAD design.
What does this mean in our PLM system?
Multiple Release Statuses
First, it means that you need a way to distinguish between something that has been fully reviewed and approved and something that has been merely frozen so that it can no longer be modified. Different release statuses are the obvious way to do that.
Different revision sequences
Second, you need a revising system that can handle the different release statuses. If your business rules say that the first full release of each part is done at rev
– and you need to freeze a revision of a CAD model so it can be used in a higher assembly you can’t be freezing rev
–. So you need some other revision identifier, perhaps numeric revs (
01, etc) are used pre-release. Or perhaps you use a baseline style revision,
Single revision sequence?
It would be interesting to hear if anyone has simply said,
revisions start at 001 and run to 999. The first released revision is the first revision with the Released status.
Freezing Part Structure
If you’re releasing a Part BOM it probably isn’t necessary to fully release or freeze the component parts. But you probably do want to freeze the structure. In other words, you may not need to freeze all the attributes of the jet engine, but you do want to freeze the fact that the plane uses two engines.
Separate Parts and Designs
I think it means that is helpful to distinguish between Parts which are what is bought and sold, and Designs which are the representations of those parts, generally as a CAD model. If you have a single record for both then you’re tying the release lifecycle of your Part data to your CAD data. The initial release of the part structure may not contain any CAD data at all. It may be just a BOM. Then again maybe you could have a single record for both but only add CAD models at a later revision.
On the other hand…
If your assemblies are small and your design times short, you might feel that this is all way too complicated for your needs. You can probably do just fine with a single item type that is both the Part and Design and insist on full bottom-up release. You’ll probably have the occasional bottleneck in your process, but the extra overhead may simply not be worth it the rest of the time.
That’s how I see it anyhow. I’m always a bit leery of making generalizations about how things like this do or should work. I know there’s lots of you out there who come from lots of different industries that are completely different from the industries I’ve worked in. I’m really curious if what I’ve said makes sense for you or not.
Please leave your thoughts on this in the comments. Thank you!