Understanding FMEA Controls: Leveraging the Value of Today
A common error in FMEA procedure is to make entries in the Controls column that the FMEA team believes need to be done, but are not currently planned or in place. Why is this error so prevalent? Maybe the question should be why do we limit entries into the prevention or detection control column to actions or methods that are currently planned or in place?
“Never mind your mistakes. One day they will become your most prized possessions.”
Definition of “Controls”
The Oxford English dictionary defines “Controls” as “a means of limiting or regulating something.”
What is the definition of “Controls” in an FMEA?
“Controls” are the methods or actions currently planned or already in place to reduce or eliminate risk. Controls can be the methods to prevent or detect the cause during product development, or can be actions to detect a problem during service before it becomes catastrophic.
Prevention-type design controls describe how a cause, failure mode, or effect in the product design is prevented based on current or planned actions; they are intended to reduce the likelihood that the problem will occur, and are used as input to the occurrence ranking.
Detection-type design controls describe how a failure mode or cause in the product design is detected, based on current or planned actions, before the product design is released to production, and are used as input to the detection ranking. Detection controls are intended to increase the likelihood that the problem will be detected before it reaches the end user.
Prevention-type Process Controls describe how a cause, failure mode or effect in the manufacturing or assembly process is prevented, based on current or planned actions. They are intended to reduce the likelihood that the problem will occur, and are used as input to the occurrence ranking.
Detection-type Process Controls describe how a failure mode or cause in the manufacturing or assembly process is detected, based on current or planned action, before the item is shipped from the manufacturing or assembly plant, and are used as an input to the detection ranking.
How are Controls identified in FMEAs?
The Design or Process FMEA team should consider what actions or methods are currently planned or in place that meet the definition of prevention or detection controls. Discussion should be limited to those actions or methods that will take place without anything being done differently by the FMEA team. If the FMEA team believes that something needs to be done differently, they should recommend the actions as part of the FMEA.
Why is it important to limit entries in the Controls column to currently planned actions or methods? Because the occurrence ranking depends in part on the entries in the prevention column, and the detection ranking depends on the entry in the detection controls column. Putting actions or methods in these columns that need to be done differently will skew the risk rankings, and miss out on the project-management benefits of Recommended Actions, such as person responsible and target completion date.
What is an example of Design FMEA controls
Item: Power steering pump
Function: Delivers hydraulic power for steering by transforming oil pressure at inlet [xx] psi) into higher oil pressure at outlet ([yy] psi) during engine idle speed
Failure Mode: Inadequate outlet pressure (less than [yy] psi)
Effect (Local: Pump): Low pressure fluid goes to steering gear
Effect (Next level: Steering Subsystem): Increased friction at steering gear
Effect (End user): Increased steering effort with potential accident during steering maneuvers
Cause: Fluid incorrectly specified (viscosity too low)
Prevention Control: Design guidelines for hydraulic fluid selection
Detection Control: Vehicle durability test #123
What is an example of Process FMEA controls
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
Prevention Control: Shaft hardening setup instructions
Detection Control: audit of shaft hardness
When identifying controls to enter into your FMEA, it is important to realize that these are the currently planned controls, not controls that have yet to be established or that will be changed. The idea is to list the controls that are in place or will be used if no changes are made to current program plans. If the FMEA team wishes to add, modify or delete design or process controls they should use the recommended action column.
If no prevention or detection controls are applicable for a given failure mode/cause, the FMEA team should leave the corresponding column blank.
In the next article, we use problems and solutions to learn about FMEA controls. In one of the problems, we continue examining the door latch-pin failure of the DC-10 cargo door, as an example to identify FMEA controls. In the advanced problem, we analyze a fictitious FMEA relating to potential safety of someone trying to unjam a snowblower.
Ask a question about FMEA
In the words of Albert Einstein, “The important thing is never to stop questioning.” I invite you to ask anything at all about the broad subject of FMEAs. You may be curious about an application issue, or want another view on a challenge you are experiencing. Questions and answers are the lifeblood of learning, and we’re are all learning. I will answer all questions to the best of my ability, and promise to keep personal information confidential.
Receive an email as each new article becomes available.