The “form fit Function” guideline helps engineers to decide whether a product change should require a new part number or simply a revision of the same part number.
(a) Interchangeable Change (b) Non-interchangeable Change
Interchangeable Change - Changes that will ensure interchangeability
Generally, this kind of change will be implemented just by revising the Part. Creating new revision and releasing that new revision by formal Engineering Change Management mechanism is the way to implement this type of change.
This kind of change will not alter/affect form, fit or function generally. i.e., this kind of change (even after implementation) will ensure interchangeability of the affected part’s new revision with its previous revision. Form Fit Function will be intact.
Consider the Following example below and here Part 4 Revision1 is used in two assemblies as shown below.
This is BOM structural change. In this case, we need to choose explicitly which are all the immediate parent Parts (BOM) affected by this change in order to subject those parent parts for Change analysis.
If the non-interchangeable change is made to a component part at a lower level in BOM structure, the part number of the component changes. In addition, the part number of each higher level assembly where that affected part is used also changes until an assembly level is reached where interchangeability is re-established with the old revision of the assembly.
Assume that the Part U in the above assembly undergoes a change which will make the part non-interchangeable with its previous revision. So we are creating new part number “Part V” instead of revising part U. This part replacement makes structural change in Assembly S. So the assembly Part S needs to be analyzed for change.
In the above example, the change to S due to replacement of one of its component is non-interchangeable with its revision 1. So we need to introduce a new Part “Part W” as replacement of Assembly S. Again assume that this replacement makes Part R to be replaced by Part X due to non-interchangeability constraint.
How long we need to continue this?
I am not attempting here to explain what is “Form Fit Function” (F3 or FFF ), but instead I will focus on the impact of this F3 factor ( interchangeability concept) on “Bill of Material” (BOM). To understand more of what is F3, please visit any of the many available web pages in internet.
We all know that “Form Fit Function” rule ensures interchangeability between different revisions of a single part number.
The change a part and its BOM undergo is of two different types with respect to the concept of interchangeability.We all know that “Form Fit Function” rule ensures interchangeability between different revisions of a single part number.
(a) Interchangeable Change (b) Non-interchangeable Change
Interchangeable Change - Changes that will ensure interchangeability
Generally, this kind of change will be implemented just by revising the Part. Creating new revision and releasing that new revision by formal Engineering Change Management mechanism is the way to implement this type of change.
This kind of change will not alter/affect form, fit or function generally. i.e., this kind of change (even after implementation) will ensure interchangeability of the affected part’s new revision with its previous revision. Form Fit Function will be intact.
Because this kind of change has much less impact on the product and also the interchangeability is intact, BOM structure can be auto-updated with new (latest released) revisions without any need of change approval process for the BOM update. In all the BOM structures, wherever the affected part is used, the affected part can be auto-updated with new (latest released) revision.
Revision should always ensure interchangeability (exceptions can be there)
Consider the Following example below and here Part 4 Revision1 is used in two assemblies as shown below.
- Part 4 Revision 1 undergoes a change that can ensure interchangeability
- This change can be implemented just by creating next revision for Part 4
- All the BOM structures wherever Part 4 is used are auto updated with new revision
The Parent Parts (Part 3 & Part 8) need not undergo any revision change by “Engineering Change Management” mechanism when the child parts in its structure are auto updated with latest revision.
Non-interchangeable Change - Change that does not ensure interchangeability
When a new change, if it could be implemented by creating new revision does not ensure interchangeability with its previous revision, we will not revise the part. But instead we need to create a new part number to implement the proposed Change.
So this kind of change is implemented by changing the part’s number. It is necessary because the change affects form, fit or function. The new revision of the part is no longer interchangeable with the old part. Hence we need to uniquely identify the part with new part number for the purpose of procurement, stocking and manufacturing.
It calls for replacement of the affected part number with a new part number in the BOM structure.
So this kind of change is implemented by changing the part’s number. It is necessary because the change affects form, fit or function. The new revision of the part is no longer interchangeable with the old part. Hence we need to uniquely identify the part with new part number for the purpose of procurement, stocking and manufacturing.
It calls for replacement of the affected part number with a new part number in the BOM structure.
This is BOM structural change. In this case, we need to choose explicitly which are all the immediate parent Parts (BOM) affected by this change in order to subject those parent parts for Change analysis.
If the non-interchangeable change is made to a component part at a lower level in BOM structure, the part number of the component changes. In addition, the part number of each higher level assembly where that affected part is used also changes until an assembly level is reached where interchangeability is re-established with the old revision of the assembly.
In the below example, Part D Revision 1 is used in two assemblies as shown below.
“Part D Revision 1” undergoes a change which does not ensure interchangeability with its Rev 1. As interchangeability (FFF) could not be ensured by revising the part, we should not attempt to revise the part but we need to create new part number (Assume “Part F “ ).
Now we need to explicitly choose the BOM where Part D needs to be replaced with Part F. (May be all the BOMs too). Assume Assembly C is impacted where component D needs to be replaced by Component F.
Due to this structural Change, we need to analysis the change impact on parent Part C with respect to interchangeability. Now assume that Part C Revision 2 is interchangeable with its previous revision. (If not we may need to go for new part number for the parent to replace Part C. )
Now we need to explicitly choose the BOM where Part D needs to be replaced with Part F. (May be all the BOMs too). Assume Assembly C is impacted where component D needs to be replaced by Component F.
Due to this structural Change, we need to analysis the change impact on parent Part C with respect to interchangeability. Now assume that Part C Revision 2 is interchangeable with its previous revision. (If not we may need to go for new part number for the parent to replace Part C. )
Let us consider another example:
In the above example, the change to S due to replacement of one of its component is non-interchangeable with its revision 1. So we need to introduce a new Part “Part W” as replacement of Assembly S. Again assume that this replacement makes Part R to be replaced by Part X due to non-interchangeability constraint.
How long we need to continue this?
A new part number needs to be assigned to the next higher assembly for the changed part and to all subsequent higher assemblies up to and including the level at which interchangeability is reestablished.
In the example, Interchangeability is reestablished in top level Part P. So Part P is revised to become revision 2.
In the example, Interchangeability is reestablished in top level Part P. So Part P is revised to become revision 2.
I hope my attempt in this blog will help you to understand the impact of "interchangeability" concept on BOM.
Your comments are appreciated.
