For today’s blog post, we will be discussing the importance of when to change part numbers and revisions on manufacturing drawings. This is a major part of engineering change control and maintaining the proper documentation based on the minor and major changes made. Before we get started, it is important to mention that this blog is not meant as a “how to” of maintaining documentation and engineering change control. Many OEMs and companies maintain their document control based on their own system of rules of configuration or interchangeability (when to change part numbers, how to properly roll revisions, what letters and numbers to use, etc.).
It is agreeable that good configuration management is essential. The most important deciding factor of when to change part numbers or revisions should be based on the principles of interchangeability to your bill of materials. Sometimes companies will go off on a whim and change the part number or the revision, and not take into consideration of what that change will impact. Manufacturing drawings, parts lists, bill of materials, and drawing trees all represent how components, materials, sub-assemblies, and assemblies come together to create the end product. Therefore changing something like a part number, is a drastic change in the grand scheme of things compared to a revision change. So it is important to have rules and guidelines in place of when those important aspects of a drawing change and how to properly incorporate the change.
At VIP, we’ve seen it all. A company that we have been fabricating parts for will all of a sudden change the part number because a piece of hardware or paint color changed. This situation from a manufacturing point of view, is very cumbersome and not necessary since the actual fabrication aspect has not changed. Generally speaking, unless the part is no longer interchangeable (fit, form, and function are identical), there is no reason to change the part number. Instead, the revision should be rolled (hardware change) or a dash number added to the part number (color change) if there are multiple colors. By changing the part number, all the corresponding documentation like the drawings, sub-assemblies, assemblies, bill of materials, drawing trees, parts lists, manufacturing plans all have to be changed in order to incorporate the new part number, which is not necessary and costly since the part is still interchangeable.
Although rules for configuration changes are based on the industry and company, the rules are generally based on classes of change in relation to the influences of changes to the bill of materials. As mentioned above, the severity of the change relative to the fit, form, function, and interchangeability are classified as Class I. All Class I changes indicate a part number change because the part is no longer interchangeable if the fit, form, function are not the same, and therefore needs to be uniquely identified. Whereas Class II changes are minor changes to documentation or hardware that do not require a part number change, but rather a revision change.
If a Class I change only affects a single part at the first and only level, then only that part number would change. Whereas, in very complex bill of materials that involve intricate assemblies, Class I changes will affect not only the part with the change, but also any part numbers of each higher level assembly that uses the changed part until the assembly becomes interchangeable. This can become a very difficult to track, manage, and maintain which is why is it so important to strictly follow the change rules. Otherwise, configuration management can easily become a disaster when the parts are manufactured.
If you have any tips on how you maintain changes in manufacturing documentation, feel free to share below. Be sure to include the industry you’re from and how you classify changes. Thank you for following along.