Identifications, Part Numbers, Documents, Revisions. Despite initial simplicity these terms are often create confusion in organizations and lead to additional misunderstanding. Design and Motion blog post When a version is just a version and a revision is more made me think again about differences between document revisions / version and part lifecycle. In my earlier post – BOM 101: 5 “Don’ts” for Bill of Materials Management, I’ve been talking about differences between Part Numbers and Document Numbers. One of my “don’t” recommendation was not to use the same numbers for documents and parts. Design and Motion article gives a good explanation why it is important. Every PDM system (article speaks about Autodesk Vault, but it will be similar for other PDMs) is allowing to use revisions and versions for CAD and other documents. Here is passage explaining the difference
A version is an iteration, something that is different than before.When programmers develop software a version is typically a minor software update, something that addresses issues in the the original release but does not contain enough to warrant a major release of the software. A revision is a controlled version. Webster’s dictionary describes a “revision” as the act of revising, which is to make a new, amended, improved, or up-to-date version. Back to the software analogy, a revision is seen as a major release of the software. Something that introduces new features and functionality, as well as fixing bugs. In the engineering world we use revisions to document the changes so that anyone can understand what was changed. Versions are usually temporary, revisions are permanent. What I mean by this is that during the design phase I will quickly build up versions of the design, however 5-years from now I will only care about one version, the one that was released.
So, typical document (e.g CAD assembly or drawing) will have document number and additional version / revision. One of the common mistakes (especially in small companies) to use document number as identification for parts. This is wrong. The right identification for parts is Part Number. Parts have no versions and revisions. The lifecycle schema for parts can contain revision as a property as well as reference to document (including document revision). In order to manage differences between part and lifecycle, companies are using interchangeability model. Usually, unique part number is identifying part until both parts can be mixed in the same bin location. As soon as next design or other change will make a change, new part number will be assigned to the part. Two parts can be considered as “interchangeable”. It means the functional and physical properties are equivalent in performance, reliability and maintainability. Based on that, two parts can be used without requiring special procedures (such as selecting for fit or performance) and without altering the part itself or any other part. In addition to Part Number, lifecycle status can be applied to the part to identify the level of maturity. Typical examples of lifecycle statuses are – pre-release, production, last time buy, obsolete and some others.
Management part lifecycle is completely different document versions and revisions. These are separate processes. The alignment between them can be set by assignment of specific document revision to be related to design of a specific Part (Part Number). This relation can be set inside of PDM/PLM system (in case system manage both documents and parts). In case part lifecycle managed by another system (e.g. ERP), that system will be responsible to establish relationships between released documents (drawing) representing a specific Part number.
What is my conclusion? Despite visible simplicity, it is absolutely important to separate document and part lifecycle in every PDM / PLM implementation. Document number and Part number cannot be identical. The special mechanism allowing linking between specific Part (number) and released document (including revision) should be implemented. It is important to set this rules from the early beginning to prevent future part / documents management mess. Just my thoughts…