failure modes, effects & criticality analysis (fmeca)
FAILURE MODES, EFFECTS & ANALYSIS - FMEA
A product should have… Long service life During this life, it should have few failures
A product should be Reliable To achieve a required level of reliability, certain techniques are necessary, one of which is Failure Modes and Effects Analysis (FMEA).
Failure modes and effects analysis is a methodology to identify and analyze: All potential failure modes of the various parts of a system The effects these failures may have on the system How to avoid the failures, and/or mitigate the effects of the failures on the system FMECA is a technique used to identify, prioritize and eliminate potential failures from the system, design or process before they reach the customer. - Omdahl (1988)
Failure Mode any design flaw, out-of-spec condition, or change in a product / process which prevents it from functioning properly Example:
Process: ATM Pin Authentication Failure mode: Unauthorized access; Authentication failure
Key Elements
Timeliness
- “Before the event action” and not an “After the fact” exercise
Teamwork
- Reviewed by a team of individuals with diverse experience & expertise
Documentation
- “Living Document”
Benefits Reduces the number of product failures experienced by the customer
Product/ Process Robustness Reduced costs (materials, re-work, late change, recalls etc.)
Standardized approach to risk assessment and reduction Enhances teamwork, understanding and crossfunctional working relationships Identification of critical areas of the system (Root Cause Analysis)
FMEA answers the following Qs: What function(s) is the product suppose to perform How could the product fail to perform that function
What effect would the failure have on the end product and the end user How severe is the effect What could cause the failure
How likely is the cause to actually result in the failure mode What is being done to prevent or detect the cause How effective is this prevention or detection method
What is the overall risk associated with the failure mode What corrective actions can be taken to eliminate the cause of the failure or to improve the prevention or detection measure, and thus reduce the risk
Types Design FMEA Carried out to eliminate failures during product design, taking into account all types of failures during the whole life-span of the equipment
Process FMEA
Focused on problems stemming from how the product is manufactured, maintained or operated
System FMEA
Looks for potential problems and bottlenecks in larger processes, such as entire production lines
Approaches to FMEA Bottom-up approach • The bottom-up approach is used when a system concept has been decided. Each component on the lowest level of components are studied one-by-one. • Also called the Hardware approach
Top-down approach • Mainly used in an early design phase before the whole system structure is decided • Analysis start with the main system function- and how these may fail. • Functional failures with significant effects are usually prioritized in the analysis
Functional Block Diagram • A functional block diagram is used to show how the different parts of the system interact with one another to verify the critical path. • It is recommended to break the system down to different levels. • Review schematics and/or other engineering drawings of the system to show how different parts interface with one another by their critical support systems to understand the normal functional flow requirements.
• A list of all functions of the equipment is prepared before examining the potential failure modes of each of those functions. • Operating conditions (such as; temperature, loads, and pressure), and environmental conditions may be included in the components list. • A bottom-up approach is used where by analysis begins at the component level, followed by analysis of subsequent or higher system levels.
Functional Block Diagram
Elements of the FMEA Form 1. In the first column, a unique reference to an element (subsystem or component) is given. It may be a reference to an id. In a specific drawing, a so-called tag number, or the name of the element.
2. The functions of the element are listed. It is important to list all functions. A checklist maybe useful to secure that all functions are covered. 3. The various operational modes for the element are listed. Example of operational modes are: idle, standby, and running. In applications, where it is not relevant to distinguish between operational modes, this column maybe omitted.
4. For each function and operational mode of an element, the potential failure modes have to be identified and listed. Note that a failure mode should be defined as a non-fulfillment of the functional requirements of the functions specified in column 2. 5. The failure modes identified in column 4 are studied one-by-one. The failure mechanisms (e.g.,corrosion, erosion, fatigue) that may produce or contribute to a failure mode are identified and listed. Other possible causes of the failure mode should also be listed.
Elements of the FMEA Form 6. The various possibilities for detection of the identified failure modes are listed. These may involve diagnostic testing, different alarms, proof testing, human perception, and the like. Detection - The ability of the current control scheme to detect or prevent a given cause Detection is sometimes termed EFFECTIVENESS. It is a numerical subjective estimate of the effectiveness of the controls to prevent or detect the cause or failure mode before the failure reaches the customer. The assumption is that the cause has occurred.
Elements of the FMEA Form 7. The effects each failure mode may have on other components in the same subsystem and on the subsystem as such (local effects) are listed. 8. The effects each failure mode may have on the system (global effects) are listed. The resulting operational status of the system after the failure may also be recorded, that is, whether the system is functioning or not, or is switched over to another operational mode. In some applications, it maybe beneficial to consider each category of effects separately, like: safety effects, environmental effects, production availability effects, economic effects, and soon.
9. Failure rates for each failure mode are listed (Occurrence).
Elements of the FMEA Form 10. The severity of a failure mode is the worst potential (but realistic) effect of the failure considered on the system level (the global effects)
11. Possible actions to correct the failure and restore the function or prevent serious consequences are listed. Actions that are likely to reduce the frequency of the failure modes should also be recorded. 12. The last column may be used to record pertinent information not included in the other columns.
Risk Ranking The risk related to the various failure modes is often presented either by a : Risk matrix, or a Risk priority number (RPN)
RISK MATRIX
Risk Priority Number O = the rank of the occurrence of the failure mode S = the rank of the severity of the failure mode D = the rank of the likelihood that the failure will be detected before the system reaches the end-user/customer
RPN = O x S x D
The smaller the RPN the better – and – the larger the worse.
Selection of Actions The risk may be reduced by introducing
Design changes Engineered safety features Safety devices Warning devices Procedures/training
RPN Reduction
Step 1: For Each Input, Determine the Potential Failure Modes
Step 2: For Each Failure Mode, Identify Effects and Assign Severity
Step 3: Identify Potential Causes of Each Failure Mode and Assign Score
Step 4: List Current Controls for Each Cause and Assign Score
Step 5: Calculate RPNs
Step 6: Develop Recommended Actions, Assign Responsible Persons, and Take Actions
Step 7: Assign the Predicted Severity, Occurrence, and Detection Levels and Compare RPNs
- END Additional Readings on FMEA http://www2.warwick.ac.uk/fac/sci/wmg/ftmsc/modul es/modulelist/peuss/slides/section_10b_fmea_lecture_ slides_compatibility_mode.pdf
A product should have… Long service life During this life, it should have few failures
A product should be Reliable To achieve a required level of reliability, certain techniques are necessary, one of which is Failure Modes and Effects Analysis (FMEA).
Failure modes and effects analysis is a methodology to identify and analyze: All potential failure modes of the various parts of a system The effects these failures may have on the system How to avoid the failures, and/or mitigate the effects of the failures on the system FMECA is a technique used to identify, prioritize and eliminate potential failures from the system, design or process before they reach the customer. - Omdahl (1988)
Failure Mode any design flaw, out-of-spec condition, or change in a product / process which prevents it from functioning properly Example:
Process: ATM Pin Authentication Failure mode: Unauthorized access; Authentication failure
Key Elements
Timeliness
- “Before the event action” and not an “After the fact” exercise
Teamwork
- Reviewed by a team of individuals with diverse experience & expertise
Documentation
- “Living Document”
Benefits Reduces the number of product failures experienced by the customer
Product/ Process Robustness Reduced costs (materials, re-work, late change, recalls etc.)
Standardized approach to risk assessment and reduction Enhances teamwork, understanding and crossfunctional working relationships Identification of critical areas of the system (Root Cause Analysis)
FMEA answers the following Qs: What function(s) is the product suppose to perform How could the product fail to perform that function
What effect would the failure have on the end product and the end user How severe is the effect What could cause the failure
How likely is the cause to actually result in the failure mode What is being done to prevent or detect the cause How effective is this prevention or detection method
What is the overall risk associated with the failure mode What corrective actions can be taken to eliminate the cause of the failure or to improve the prevention or detection measure, and thus reduce the risk
Types Design FMEA Carried out to eliminate failures during product design, taking into account all types of failures during the whole life-span of the equipment
Process FMEA
Focused on problems stemming from how the product is manufactured, maintained or operated
System FMEA
Looks for potential problems and bottlenecks in larger processes, such as entire production lines
Approaches to FMEA Bottom-up approach • The bottom-up approach is used when a system concept has been decided. Each component on the lowest level of components are studied one-by-one. • Also called the Hardware approach
Top-down approach • Mainly used in an early design phase before the whole system structure is decided • Analysis start with the main system function- and how these may fail. • Functional failures with significant effects are usually prioritized in the analysis
Functional Block Diagram • A functional block diagram is used to show how the different parts of the system interact with one another to verify the critical path. • It is recommended to break the system down to different levels. • Review schematics and/or other engineering drawings of the system to show how different parts interface with one another by their critical support systems to understand the normal functional flow requirements.
• A list of all functions of the equipment is prepared before examining the potential failure modes of each of those functions. • Operating conditions (such as; temperature, loads, and pressure), and environmental conditions may be included in the components list. • A bottom-up approach is used where by analysis begins at the component level, followed by analysis of subsequent or higher system levels.
Functional Block Diagram
Elements of the FMEA Form 1. In the first column, a unique reference to an element (subsystem or component) is given. It may be a reference to an id. In a specific drawing, a so-called tag number, or the name of the element.
2. The functions of the element are listed. It is important to list all functions. A checklist maybe useful to secure that all functions are covered. 3. The various operational modes for the element are listed. Example of operational modes are: idle, standby, and running. In applications, where it is not relevant to distinguish between operational modes, this column maybe omitted.
4. For each function and operational mode of an element, the potential failure modes have to be identified and listed. Note that a failure mode should be defined as a non-fulfillment of the functional requirements of the functions specified in column 2. 5. The failure modes identified in column 4 are studied one-by-one. The failure mechanisms (e.g.,corrosion, erosion, fatigue) that may produce or contribute to a failure mode are identified and listed. Other possible causes of the failure mode should also be listed.
Elements of the FMEA Form 6. The various possibilities for detection of the identified failure modes are listed. These may involve diagnostic testing, different alarms, proof testing, human perception, and the like. Detection - The ability of the current control scheme to detect or prevent a given cause Detection is sometimes termed EFFECTIVENESS. It is a numerical subjective estimate of the effectiveness of the controls to prevent or detect the cause or failure mode before the failure reaches the customer. The assumption is that the cause has occurred.
Elements of the FMEA Form 7. The effects each failure mode may have on other components in the same subsystem and on the subsystem as such (local effects) are listed. 8. The effects each failure mode may have on the system (global effects) are listed. The resulting operational status of the system after the failure may also be recorded, that is, whether the system is functioning or not, or is switched over to another operational mode. In some applications, it maybe beneficial to consider each category of effects separately, like: safety effects, environmental effects, production availability effects, economic effects, and soon.
9. Failure rates for each failure mode are listed (Occurrence).
Elements of the FMEA Form 10. The severity of a failure mode is the worst potential (but realistic) effect of the failure considered on the system level (the global effects)
11. Possible actions to correct the failure and restore the function or prevent serious consequences are listed. Actions that are likely to reduce the frequency of the failure modes should also be recorded. 12. The last column may be used to record pertinent information not included in the other columns.
Risk Ranking The risk related to the various failure modes is often presented either by a : Risk matrix, or a Risk priority number (RPN)
RISK MATRIX
Risk Priority Number O = the rank of the occurrence of the failure mode S = the rank of the severity of the failure mode D = the rank of the likelihood that the failure will be detected before the system reaches the end-user/customer
RPN = O x S x D
The smaller the RPN the better – and – the larger the worse.
Selection of Actions The risk may be reduced by introducing
Design changes Engineered safety features Safety devices Warning devices Procedures/training
RPN Reduction
Step 1: For Each Input, Determine the Potential Failure Modes
Step 2: For Each Failure Mode, Identify Effects and Assign Severity
Step 3: Identify Potential Causes of Each Failure Mode and Assign Score
Step 4: List Current Controls for Each Cause and Assign Score
Step 5: Calculate RPNs
Step 6: Develop Recommended Actions, Assign Responsible Persons, and Take Actions
Step 7: Assign the Predicted Severity, Occurrence, and Detection Levels and Compare RPNs
- END Additional Readings on FMEA http://www2.warwick.ac.uk/fac/sci/wmg/ftmsc/modul es/modulelist/peuss/slides/section_10b_fmea_lecture_ slides_compatibility_mode.pdf
