FFF (Form, Fit, Function). Revisions and Interchangeability

FFF (Form, Fit, Function). Revisions and Interchangeability

I had a conversion earlier this week about the BOM revision process. I used the abbreviation “FFF” in my response and got a question – what is FFF? This magic abbreviation is used quite often in manufacturing – FFF and it stands for “Form, Fit, Function). If you never heard about it until now, take some time to read this article and reference materials. Because it can save you a lot of time asking questions and most importantly, making mistakes when you work on your next projects. Let me explain to you why and also how to avoid these mistakes. The topic is not simple and I’m coming to discuss it again, because each time we say FFF and UpRev, it ignites the debates. Check out The Bloodbath of Debates about FFF and revisions.

Identification is one of the most fundamental elements of configuration management. It helps you to define the “item” and its paraments (eg. Part Number and Revision). Once it is done, you can define a set of rules to change it when it is needed. It all comes to the point of changes and how to identify what change will cause the need to issue the new part number or next revision. These processes can happen in product development and also during the production and for released products.

So, the Form, Fit, Function (FFF) factor describes the criteria or characteristic of the component or an entire assembly from the identification standpoint. Here is the challenge, it is hard to quantify. Usually, it is defined as a “change that is significant” enough, has the same form, cannot fit the same shape/compartment,  or performs a different set of functions. Now apply it to your product and you can get an idea of why it is not so simple to define. I was observing long debates in engineering and manufacturing teams about interchangeability.

Form – it is usually the shape, geometry, and other parameters such as dimensions, mass, visual appearance, etc. The “rule of the blind man” says that you should be able to pick the part from the bin with a specific part number without visually checking the part. If you cannot do it, you need to separate them.

Fit – It is also related to dimension and shape, but attributed to the external interface and how the part of assembly connects or becomes a part of the other assembly or part. Think about the dimensions of the screw, chip, or compartment size to insert the A/C unit to get an idea of what is that.

Function – these criteria describe how the unit or components perform. It can be strength, capacity, or functional operation (eg. electrical motor speed).

You need to analyze all these parameters to decide if the change you’re making will be interchangeable (means item has the same form, fit, and function) or not. In the second case, you need to issue a new Part Number or revise.

What is the problem? Why can’t you just keep revisions or part numbers go?

If you in doubt, change the revision or issue a new part number? The answer is simple – time and money. Although part numbers are cheap, the change is not. So, by performing the change, the formal change management process can kick-off and it will cause the updates of many pieces of information- ECOs, Drawings, etc. If you understand your company process, you can then decide when to do so. Both extremes are bad. Don’t revise or change the part number and you will get screwed by installing the wrong piece of equipment or sending the part that doesn’t fit your maintenance crew. Always revise and you will need to spend a lot of money to maintain documentation and handle changing and other processes.

What is needed from PLM software to support it?

The software to support changes must have the ability to identify the item and maintain the history of changes including immutable revisions. The record must be reliable and configurable to support a company schema for part numbers and revisions. The last is not simple, because debates about semantically meaningful (aka smart) part numbers and “just numbers” are still here. Check this article – 4 reasons why companies are still using intelligent part numbers.

Revision mechanism is a second part of the software requirements and it can be tricky in structured product representations (eg. multi-level BOMs). It usually comes down to the following main processes – (1) top-down, when you need to apply a new revision to all sub-level items and (2) when you need to UpRev the higher-level assembly and (3) how to pick the new revision of the sub-levels when you revise the assembly. You can read more about both top-down and bottom-up processes here.

What is my conclusion?

The art of FFF is to define the set of criteria used in your product development and manufacturing, which gives you the ability to identify Items and to make changes. It includes the ability to decide when to use a new Part Number and Revision. Sounds simple? Well, it is not because it will trigger the discussions about how to organize (or reorganize) a product development and manufacturing process in your company. And it is not simple. Just my thoughts…

Best, Oleg

Disclaimer: I’m co-founder and CEO of OpenBOM developing a digital network-based platform that manages product data and connects manufacturers and their supply chain networksMy opinion can be unintentionally biased.


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