If you work with BOMs in Teamcenter you have probably seen the terms Precise and Imprecise BOM structure. Even if you only use one type of BOM you need to understand the difference between them.
BOM View Revisions
In Teamcenter an assembly structure is represented by a BOM View. BOM Views are associated with Items, and each Item Revision will have it’s Revision of the BOM View — a BOM View Revision, or BVR.
imprecise apply to BOM view revisions. It is determined by an attribute of the BOM view revision business object.
What does Precise and Imprecise BOM Mean?
A BOM View Revision defines which components are used by a particular Item Revision.
imprecise describe what is meant by
component. If a BVR is precise the components are item revisions; the BVR defines precisely which revision is used by the structure. If the assembly is imprecise the components are items; the BVR is not precise about the revision to which the assembly refers.
Why Precise Structures are Important
When you release an assembly, releasing the precise structure preserves the record of exactly what it was that was developed, approved and released. It is an important historical artifact, particularly of the CAD data.
This post will be too long if I discuss revision rules in detail. The main thing to know though is that even if an assembly is precise, you can still configure it to load latest working revisions or latest released or whatever by picking the appropriate revision rule. Basically, you can choose to look as the structure
precisely as it was last updated, or
imprecisely using which ever revision fulfills your selection criteria.
What Use is an Imprecise Structure?
An imprecise structure represents how someone assembling a product might look at the components. Often it does not matter in the factory which revision of a component is used. The rules say that every revision of a component must have the same
form, fit, and function. Therefore the individual revisions are interchangeable. The person building the assembly can select any revision that is available of the components.
(yes, there are exceptions to this. Aerospace being the prime example.)
But the factory worker is probably working from a report generated from Teamcenter and not the actual BVR. The report could be generated from a precise BVR and simply remove the revision information.
So, why have the option of Imprecise structures?
Honestly, there are many who would say that you should never use imprecise assemblies. Personally, I have not seen a situation where imprecise assemblies were required. I would never release an imprecise assembly. Your released data should be the record of exactly what was reviewed and released.
That said, I do have an idea for a use for Imprecise assemblies — but that is a topic for another post…