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FMEA (Failure Mode and Effects Analysis)

Failure Mode and Effects Analysis (FMEA) is a systematic team driven approach that identifies potential failure modes in a system, product, or manufacturing / assembly operation caused by either design or manufacturing / assembly process deficiencies. It also identifies critical or significant design or process characteristics that require special controls to prevent or detect failure modes. FMEA is a tool used to prevent problems from occurring.

Fourth Edition FMEA Manual Changes

AIAG has recently released the Fourth Edition FMEA manual. 

History of FMEA

FMEAs have been around for a very long time. Before any documented format was developed, inventors and process experts would try to anticipate what could go wrong with a design or process before it was developed or tried. The trial and error and learning from each failure was both costly and time consuming. For example: Each individual iteration of an invention might fail without a thorough thought experiment by a group of engineers or inventors and take advantage of their collective knowledge to reduce the likelihood of failure.

FMEAs were formally introduced in the late 1940’s with the introduction of the military standard 1629. Used for Aerospace / rocket development, the FMEA and the more detailed Failure Mode and Effects Criticality Analysis (FMECA) were helpful in avoiding errors on small sample sizes of costly rocket technology.

The primary push for failure prevention came during the 1960’s while developing the technology for placing a man on the moon. Ford Motor Company introduced FMEA to automotive in the late 1970’s for safety and regulatory consideration after the disastrous "Pinto" affair. Ford Motor Company also used FMEAs effectively for production improvement as well as design improvement.

The current advancement of FMEA has come from the automotive sector as FMEA’s are required for all Designs and Processes to assure the prevention of problems. Integrated into Advanced Product Quality Planning (APQP), FMEA in both Design and Process formats provide the primary risk mitigation tools in the prevention strategy. Each potential cause must be considered for its’ effect on the product or process and based on the risk, actions determined and risks revisited after actions are complete. Toyota has taken this one step further with its’ Design Review Based on Failure Modes (DRBFM) approach. DRBFM moves the user through the FMEA process by considering all intentional and incidental changes and their effects on the performance of a product or process. These changes drive potential causes which require follow-up action to resolve the risk. Design reviews are the primary place to review progress and address these risks.

Robustness analysis from Interface Matrices, Boundary Diagrams and Parameter Diagrams are extremely helpful prior to FMEA development. Noise factors and interfaces with other parts and/or systems are where a large number of failures can be found as design engineers typically focus on what they control directly. Shared interfaces are an area where many failures occur today.

FMEA Development

FMEAs are developed in three distinct phases where actions can be determined. It is also imperative to do pre-work ahead of the FMEA to assure that the Robustness and past history are included in your analysis.

Step 1 is to determine all failure modes based on the functional requirements and their effects. If the severity of the effect is a 9 or 10 (meaning safety or regulatory in nature) actions are considered to change the design or process by eliminating the Failure Mode if possible or protecting the customer from the effect.

Step 2 adds causes and Occurrences to each Failure Mode. This is the detailed development section of the FMEA process. Reviewing the probability or occurrence number in order of the highest severity and working downwards, actions are determined if the occurrence is high (> 4 for non safety and regardless of occurrence >1 when the severity is 9 or 10)

Step 3 considers testing, design verification and inspection methods. Each combination from steps 1 and 2 which are considered at risk requires the detection number to be selected. The detection number represents the ability of planned tests and inspections at removing defects or excite failure modes to fail.

FMEA Risk BlocksAfter each of these steps actions are developed. Next, Risk Priority Numbers (RPN) are calculated. Please note that RPNs are calculated after three possible action opportunities have occurred. Actions are not only determined based on RPN values. RPN threshold values do not play an important role in action development, only in action evaluation when completed.

Selecting an arbitrary RPN to fall below is both ineffective at driving change and foolhardy if the order of the improvement is not controlled (severity, occurrence, detection) steps 1.2,3 as described above.

In past years, setting an RPN would immediately be met with lower numbers without any real change or improvement. This is not preventing failure, but in fact driving bad behavior of the design and process teams required to perform the FMEA.

FMEA Exercise

Can you determine the order of need for change in the following three examples:
FMEA and the Control PlanSeverity (5), Occurrence (4), Detection (2) = 40
Severity (9), Occurrence (2), Detection (2) = 36
Severity (8), Occurrence (1), Detection (8) = 64
FMEA in selecting Special Characteristics

FMEAs are used to refine special characteristics that the design community may be concerned about as these characteristics may affect performance. These characteristics are translated into dimensions or features and provided for the Process design activity to error proof and/or develop mitigation plans to reduce risk of poor performance. The timing for this is critical to get the best benefit. Advanced Product Quality Planning (APQP) provides the concurrent and collaborative structure to accomplish this effectively. Eventually, process capability and evidence of proper Process Controls found in a control plan are required.

Benefits of FMEA

  • Improves the quality, reliability, and safety of products / services / machinery and processes
  • Improves company image and competitiveness
  • Increases customer satisfaction
  • Reduces product development timing and cost / support integrated product development
  • Documents and tracks action taken to reduce risk
  • Reduces potential for Warranty concerns
  • Integrates with Design for Manufacturing & Assembly techniques
  • Applications for FMEA
  • Process - analyze manufacturing and assembly processes.
  • Design - analyze products before they are released for production.
  • Concept - analyze systems or subsystems in the early design concept stages.
  • Equipment - analyze machinery and equipment design before they are purchased.
  • Service - analyze service industry processes before they are released to impact the customer.

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