An “Inside FMEA” reader recently asked a question on the subject of Process FMEAs, specifically whether assigning the cause as “operator error” is useful. This article will share insights into the nature of a cause in Process FMEA, and whether describing cause as “operator error” adds value.
Fred and I podcasted on this topic. Link to the podcast is here.
I’ve seen literally hundreds of Process FMEAs that list “operator error” as the cause of a process related failure mode. Let me be as clear as I can. Assigning “operator error” as the cause in a Process FMEA does not add value. I’ll explain.
It’s the Process
W. Edwards Deming teaches us to focus on the process, not the person. This is illustrated by Deming’s red bead experiment. Here is a link
Deming points out the fallacy of attributing the performance of the system merely to the performance of the individual workers in the system. “Real and sustainable improvement on the part of the willing worker is achieved only when management is able to improve the system, starting small and then expanding the scope of the improvement efforts.”
This does not mean that a deficiency in the work instructions or the training regimen is not an issue. Operator training and work instructions are both important. But, merely stating “operator error” as the cause in PFMEA is not a useful practice.
What is a Cause in Process FMEA?
Quoting from my book, Effective FMEAs, “For Process FMEAs, the cause is the manufacturing or assembly deficiency (or source of variation) that results in the failure mode.”
We’re looking for a potential deficiency in the manufacturing or assembly process.
For an example, I’ll excerpt from Effective FMEAs, chapter 3.
Process Step: Induction harden shafts using induction-hardening machine
Function: Induction harden shafts using induction-hardening machine ABC, with minimum hardness Brinell Hardness Number (BHN) “X”, according to specification #123.
Failure Mode: Shaft hardness less than BHN “X”
Effect (In plant): 100% scrap
Effect (End user): Potential shaft fracture with complete loss of performance
Cause: Induction machine electrical voltage/current settings incorrect for part number
Poorly worded example of Cause: Operator error
Note, the Cause in this example is a potential deficiency in the process. We could have said that the operator misread the induction settings. If you are concerned about an operator misreading the settings, there may be a deficiency in the process that makes it too easy to misadjust the settings. It is worth the effort to find the underlying deficiency.
Erroring proofing
It is possible to change the product design so that errors in manufacturing or assembly processing are reduced or eliminated.
The manufacturing or assembly process can be changed so that processing errors are reduced or eliminated.
A deficiency in the manufacturing or assembly process that makes it difficult to assemble or difficult to manufacture is input to a cause description.
A companion topic to this discussion is called Design for Manufacturing/Assembly. The objective of DFM/DFA is to make designs as easy to assemble as possible.
Don’t blame the operator. Improve the process.
What if you have data that shows operators make errors?
Certainly it is possible for assembly operators to make errors. The point is not whether an operator makes an error, the point is: what is the deficiency in the manufacturing or assembly process that makes the operator more likely to make an error? By locating and describing the process deficiency, the PFMEA team can take action to remedy.
Next article
The next series of articles will continue to share insights from reader questions.
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