Old practice
Revisioning of drawings and 3d models in CAD and PDM systems is an old and common practice. The practice origins from the days when drawings were drawn by hand on tracing paper. Erasing a few lines and then adding new lines, as well as updating the revision field, was the easiest and only way to change a material without having to redraw the entire drawing.
This practice remained in the CAD and PDM systems – unfortunately without considering the end-to-end process of drawings and materials.
Why revise?
Far too often engineers revise instead of creating new material numbers and assert that form-fit-function are unaffected. But what changes can actually be made on a drawing without un-affecting form-fit-function? Certainly, no measurements and no drawing lines can be changed.
The only changes complying with form-fit-function are changing minor texts (e.g. translating to additional languages) and loosening tolerances (not tightening).
The engineers may argue, that the PDM system is in control of the changes and from a pure documentation view that is correct in the engineering sphere.
Consequence of revising
However, this is not the case when it comes to ERP and warehouse systems. In general ERP systems distinct items only by the material number. A revision field might be available in the ERP system, but it has no impact on the processes. When materials are put in stock or issued from stock, there is no way to distinct which revision to choose.
Compatibility
Sometimes engineers (and production managers) believes that revising is ok as long as the new revision is backwards compatible. However, that is false assumption; service stocks may contain old items that are not compatible with newer items in a machine, and service technicians has no way to order a component based on a revision number.
Bottomline – any change of a materials specification (e.g. drawing) must derive a new material number.
