FMEA Tutorial, Failure Mode Effect Analysis
FMEA tutorial page is designed by TONEX to teach you the basic and fundamental definition, history, purposes, components, tools, and categories of failure mode and effect analysis (FMEA).
Definition and Purposes of FMEA
FMEA, short for Failure Mode and Effect Analysis, is a technique that
- Identify potential failure modes and their causes
- Detect the effect(s) of each failure mode on the system
- Evaluate the risk associated with each identified failure mode and their effects, and prioritize the issues for corrective action
- Create and implement corrective actions
In addition to the main objectives stated above, there are some less essential but still important objects as follow:
- Determining and avoiding safety hazards
- Decreasing poor/degraded performance
- Increasing the examination frequencies and verification plans (in the case of System or Design FMEAs)
- Better process control plans (in the case of Process FMEAs)
- Modifying the product design or production process
- Implementing inhibitory maintenance plans
- Setting up online analytical techniques
There are different types of methodologies associated with FMEA, including:
- Design FMEA (FMEA)
- Process FMEA (PFMEA)
- System FMEA
- Failure mode effect and critically analysis (FMECA)
- Concept FMEA
- Maintenance FMEA
- Software FMEA
- Failure mode effect and hazard analysis
Depending on where in the process you want to use FMEA, the method of FMEA can be selected from the above list in order to achieve the most effective results. For instance, if you want to apply FMEA in the product designing stage, the best option would be DFMEA, or if it is to identify the failure modes of the process, your best alternative would be PFMEA and so on.
Origin of FMEA
FMEA techniques was invented by the US Armed Forces in 1949 in the form of Mil-P 1629 to perform an assessment on failure mode effect and criticality. Later, NASA adopted the method for the Apollo space program with the goal of mitigating the risk of the mission. Upon the successful employment of FMEA by the army and NASA, Ford started using this methodology in the late 1970s to enhance the design and production process of their autos. About a decade later, in the 1980s, the Automotive Industry Action Group (AIAG) adopted FMEA to standardize the configuration and methods across the auto industry. And today, FMEA is being used broadly in various industries to enhance the quality of the products and processes and decrease the costs associated with poor quality.
FMEA Essential Components
- Items, parts, or system components
- Failure(s) and defect(s)
- Effect(s) of each failure mode on each other and on the entire system
- Cause(s) of failure
- Already existing control plan(s)
- Recommended corrective and preventive action(s)
- Implementing the action plan
The Process of FMEA
- Identifying the failure modes
- Detecting the effects associated with each failure mode
- Assigning a rate to the severity of the effects
- Identifying the causes related to the failure effects
- Assigning a rate to the occurrence level of the causes
- Seeking for the available controls of the causes
- Assigning a rate to the detection level of the causes
- Calculating the RPNs
- Coming up with corrective actions
- Assigning responsibility to the people involved in the process
- Implementing the actions plan
- Giving priority based on the calculated RPNs
- Allocating the anticipated severity, occurrence, and detection levels and compare the RPNs
Risk Analysis and PRNs Calculation
Risk Priority Number (RPN) provides a method for a prioritizing process concerns.
Failure Modes and Effects Analysis (FMEA) is used as a methodology for analyzing potential failure and reliability problems early in the development cycle to achieve reliability through design or enhancing manufacturing process.
FMEA is used to identify potential failure modes, determine their effect on the operation of the product, and identify actions to mitigate the failures, a crucial step to anticipate what might go wrong with a product or a process.
The early and consistent use of FMEAs in the design process leads to failure elimination and more reliable, safer products and systems.
PRNs is calculated based on this formula:
RPN = Severity x Occurrence x Detection
Where you need to rate:
- Severity of the effect of failure
- Likelihood of occurrence of the cause of failure
- Likelihood of the previous detection for each cause of failure
- The subjective nature of PRN
- Broken potential values of RPN
- Burdens of the detection scale
- Duplicate RPN values, due to the variety in combinations of severity, occurrence and detection ratings
- Thresholds PRN are nor reliable to
- For RPN employment, a high is automatically assumed regardless of the RPN value
FMEA Rating Examples
FMEA Standards cover Potential Failure Mode and Effects Analysis in Design (DFMEA) and Potential Failure Mode and Effects Analysis in Manufacturing and Assembly Processes (PFMEA) to assist users in the identification and mitigation of risk by providing appropriate terms, requirements, ranking charts, and worksheets.
Severity Rating Scale
(Should be tailored to meet the needs of your company.)
|Rating||Description||Definition (Severity of Effect)|
|10||Dangerously high||Failure could injure the customer or an employee.|
|9||Extremely high||Failure would create noncompliance with federal regulations.|
|8||Very high||Failure renders the unit inoperable or unfit for use.|
|7||High||Failure causes a high degree of customer dissatisfaction.|
|6||Moderate||Failure results in a subsystem or partial malfunction of the product.|
|5||Low||Failure creates enough of a performance loss to cause the customer to complain.|
|4||Very Low||Failure can be overcome with modifications to the customer’s process or product, but there is minor performance loss.|
|3||Minor||Failure would create a minor nuisance to the customer, but the customer can overcome it without performance loss.|
|2||Very Minor||Failure may not be readily apparent to the customer, but would have minor effects on the customer’s process or product.|
|1||None||Failure would not be noticeable to the customer and would not affect the customer’s process or product.|
Occurrence Rating Scale
(Should be tailored to meet the needs of your company.)
|Rating||Description||Potential Failure Rate|
|10||Very High: Failure is almost inevitable.||More than one occurrence per day or a probability of more than three occurrences in 10 events (Cpk < 0.33).|
|9||High: Failures occur almost as often as not.||One occurrence every three to four days or a probability of three occurrences in 10 events (Cpk ≈ 0.33).|
|8||High: Repeated failures.||One occurrence per week or a probability of 5 occurrences in 100 events (Cpk ≈ 0.67).|
|7||High: Failures occur often.||One occurrence every month or one occurrence in 100 events (Cpk ≈ 0.83).|
|6||Moderately High: Frequent failures.||One occurrence every three months or three occurrences in 1,000 events (Cpk ≈ 1.00).|
|5||Moderate: Occasional failures.||One occurrence every six months to one year or five occurrences in 10,000 events (Cpk ≈ 1.17).|
|4||Moderately Low: Infrequent failures.||One occurrence per year or six occurrences in 100,000 events (Cpk ≈ 1.33).|
|3||Low: Relatively few failures.||One occurrence every one to three years or six occurrences in ten million events (Cpk ≈ 1.67).|
|2||Low: Failures are few and far between.||One occurrence every three to five years or 2 occurrences in one billion events (Cpk ≈ 2.00).|
|1||Remote: Failure is unlikely.||One occurrence in greater than five years or less than two occurrences in one billion events (Cpk > 2.00).|
Detection Rating Scale
(Should be tailored to meet the needs of your company.)
|10||Absolute Uncertainty||The product is not inspected or the defect caused by failure is not detectable.|
|9||Very Remote||Product is sampled, inspected, and released based on Acceptable Quality Level (AQL) sampling plans.|
|8||Remote||Product is accepted based on no defectives in a sample.|
|7||Very Low||Product is 100% manually inspected in the process.|
|6||Low||Product is 100% manually inspected using go/no-go or other mistake-proofing gauges.|
|5||Moderate||Some Statistical Process Control (SPC) is used in process and product is final inspected off-line.|
|4||Moderately High||SPC is used and there is immediate reaction to out-of-control conditions.|
|3||High||An effective SPC program is in place with process capabilities (Cpk) greater than 1.33.|
|2||Very High||All product is 100% automatically inspected.|
|1||Almost Certain||The defect is obvious or there is 100% automatic inspection with regular calibration and preventive maintenance of the inspection equipment.|
FMEA includes review of the following:
Steps in the process
- Failure modes (What could go wrong?)
- Failure causes (Why would the failure happen?)
- Failure effects (What would be the consequences of each failure?)
- Analyze the current process and evaluate the potential impact of changes under consideration: teams could use the FMEA Tool to discuss and analyze the steps of a process, consider changes, and calculate the Risk Priority Number (RPN) of changes under consideration.
- Track improvement over time: calculate the total RPN for a process and then track the RPN over time to see if changes being made to the process are leading to improvement.
- For each failure mode, determine impact or effect on the product or operation using criteria table (next slide)
- Rate this impact in the column labeled SEV (severity)
- Risk factors of Severity (S), Occurrence (O) and Detection (D)
- FMEA Scoring, Calculate new RPN number :
- RPN or Risk Priority Number
- Severity x Occurrence x Detection= RPN
- Failure, the termination of a system, product or process ability to perform a required function
- Failure Mode: effect by which a failure is observed on the failed item
- Failure Cause including physical processes, design defects, quality defects, part misapplication or anything else as a basic reason for failure or that initiate the physical process by which deterioration proceeds to failure.
- Failure Effect as consequence(s) a failure mode has on the operation, function, or status of an item.
Use of design and process FMEA illustrate benefits to consumers and manufacturers. FMEA methodology is a proven technique used in the prevention and mitigation of potential failure modes. Reduced Risk Priority Number (RPN) used as the key indicator.
Example of Steps in the FMEA Process
- Identify and List potential failures and their corresponding effects. It is not unusual for a FMEA to list many different potential failures.
- FMEA is a bottom up failure analysis approach typically starts from subsystems and components leading to system failures
- List potential effects or consequences of the failures rated on a scale of 1 to 10.
- Assign Severity ratings.
- Assign Occurrence ratings.
- Assign detection rating.
- Calculate RPN (RPN as a measure of risk).
- Develop an action plan to address high RPN’
- High RPN’s warrant corrective actions.
- Take corrective action.
- Reevaluate the RPN after the actions are completed.
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