Which Purpose Describes The Failure Mode Effects Analysis

How to Perform Failure Mode and Effects Analysis (FMEA)

FMEA is performed in seven steps, with key activities at each step. The steps are separated to assure that only the appropriate team members for each step are required to be present. The FMEA approach used by Quality-One has been developed to avoid typical pitfalls which make the analysis slow and ineffective. The Quality-One Three Path Model allows for prioritization of activity and efficient use of team time.

There are Seven Steps to Developing an FMEA:

1. FMEA Pre-Work and Assemble the FMEA Team
2. Path 1 Development (Requirements through Severity Ranking)
3. Path 2 Development (Potential Causes and Prevention Controls through Occurrence Ranking)
4. Path 3 Development (Testing and Detection Controls through Detection Ranking)
5. Action Priority & Assignment
6. Actions Taken / Design Review
7. Re-ranking RPN & Closure

The Steps for conducting FMEA are as follows:

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1. FMEA Pre-Work and Assembly of the FMEA Team

Pre-work involves the collection and creation of key documents. FMEA works smoothly through the development phases when an investigation of past failures and preparatory documents is performed from its onset. Preparatory documents may include:

• Failure Mode Avoidance (FMA) Past Failure
  • Eight Disciplines of Problem Solving (8D)
• Boundary/Block Diagram (For the DFMEA)
• Parameter Diagram (For the DFMEA)
• Process Flow Diagram (For the PFMEA)
• Characteristics Matrix (For the PFMEA)

A pre-work Checklist is recommended for an efficient FMEA event. Checklist items may include:

• Requirements to be included
• Design and / or Process Assumptions
• Preliminary Bill of Material / Components
• Known causes from surrogate products
• Potential causes from interfaces
• Potential causes from design choices
• Potential causes from noises and environments
• Family or Baseline FMEA (Historical FMEA)
• Past Test and Control Methods used on similar products

1. Path 1 Development- (Requirements through Severity Ranking)

Path 1 consists of inserting the functions, failure modes, effects of failure and Severity rankings. The pre-work documents assist in this task by taking information previously captured to populate the first few columns (depending on the worksheet selected) of the FMEA.

• Functions should be written in verb-noun context. Each function must have an associated measurable. Functions may include:
  • Wants, needs and desires translated
  • Specifications of a design
  • Government regulations
  • Program-specific requirements
  • Characteristics of product to be analyzed
  • Desired process outputs
• Failure Modes are written as anti-functions or anti-requirements in five potential ways:
  • Full function failure
  • Partial / degraded function failure
  • Intermittent function failure
  • Over function failure
  • Unintended function failure
• Effects are the results of failure, where each individual effect is given a Severity ranking. Actions are considered at this stage if the Severity is 9 or 10
  • Recommended Actions may be considered that impact the product or process design addressing Failure Modes on High Severity Rankings (Safety and Regulatory)

1. Path 2 Development – (Potential Causes and Prevention Controls through Occurrence Ranking)

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Causes are selected from the design / process inputs or past failures and placed in the Cause column when applicable to a specific failure mode. The columns completed in Path 2 are:

• Potential Causes / Mechanisms of Failure
• Current Prevention Controls (i.e. standard work, previously successful designs, etc.)
• Occurrence Rankings for each cause
• Classification of Special Characteristics, if indicated
• Actions are developed to address high risk Severity and Occurrence combinations, defined in the Quality-One Criticality Matrix

1. Path 3 Development- (Testing and Detection Controls through Detection Ranking)

Path 3 Development involves the addition of Detection Controls that verify that the design meets requirements (for Design FMEA) or cause and/or failure mode, if undetected, may reach a customer (for Process FMEA).

• The columns completed in Path 3 are:
  • Detection Controls
  • Detection Ranking
• Actions are determined to improve the controls if they are insufficient to the Risks determined in Paths 1 and 2. Recommended Actions should address weakness in the testing and/or control strategy.
• Review and updates of the Design Verification Plan and Report (DVP&R) or Control Plans are also possible outcomes of Path 3.

1. Action Priority & Assignment

The Actions that were previously determined in Paths 1, 2 or 3 are assigned a Risk Priority Number (RPN) for action follow-up.

RPN is calculated by multiplying the Severity, Occurrence and Detection Rankings for each potential failure / effect, cause and control combination. Actions should not be determined based on an RPN threshold value. This is done commonly and is a practice that leads to poor team behavior. The columns completed are:

• Review Recommended Actions and assign RPN for additional follow-up
• Assign Actions to appropriate personnel
• Assign action due dates

1. Actions Taken / Design Review

FMEA Actions are closed when counter measures have been taken and are successful at reducing risk. The purpose of an FMEA is to discover and mitigate risk. FMEAs which do not find risk are considered to be weak and non-value added. Effort of the team did not produce improvement and therefore time was wasted in the analysis.

1. Re-Ranking RPN and Closure

After successful confirmation of Risk Mitigation Actions, the Core Team or Team Leader will re-rank the appropriate ranking value (Severity, Occurrence or Detection). The new rankings will be multiplied to attain the new RPN. The original RPN is compared to the revised RPN and the relative improvement to the design or process has been confirmed. Columns completed in Step 7:

• Re-ranked Severity
• Re-ranked Occurrence
• Re-ranked Detection
• Re-ranked RPN
• Generate new Actions, repeating Step 5, until risk has been mitigated
• Comparison of initial RPN and revised RPN

FMEA Document Analysis

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Deciding when to take an action on the FMEA has historically been determined by RPN thresholds. Quality-One does not recommend the use of RPN thresholds for setting action targets. Such targets are believed to negatively change team behavior because teams select the lowest numbers to get below the threshold and not actual risk, requiring mitigation.

The analysis of an FMEA should include multiple level considerations, including:

• Severity of 9 / 10 or Safety and Regulatory alone (Failure Mode Actions)
• Criticality combinations for Severity and Occurrence (Cause Actions)
• Detection Controls (Test and Control Plan Actions)
• RPN Pareto

When completed, Actions move the risk from its current position in the Quality-One FMEA Criticality Matrix to a lower risk position.

RPN Action Priority

When risk is determined to be unacceptable, Quality-One recommends a priority of action to be applied as follows:

1. Error Proofing (Eliminate Failure Mode or Address Cause)
   • Failure Mode (Only Severity of 9 or 10)
   • Causes with High Occurrence
2. Improve Potential Process Capability
   • Increase Tolerance (Tolerance Design)
   • Reduce Variation of the Process (Statistical Process Control and Process Capability)
3. Improve Controls
   • Mistake Proofing of the tooling or process
   • Improve the inspection / evaluation techniques

FMEA Relationship to Problem Solving

The Failure Modes in a FMEA are equivalent to the Problem Statement or Problem Description in Problem Solving. Causes in a FMEA are equivalent to potential root causes in Problem Solving. Effects of failure in a FMEA are Problem Symptoms in Problem Solving. More examples of this relationship are:

• The problem statements and descriptions are linked between both documents. Problem solving methods are completed faster by utilizing easy to locate, pre-brainstormed information from an FMEA.
• Possible causes in an FMEA are immediately used to jump start Fishbone or Ishikawa diagrams. Brainstorming information that is already known is not a good use of time or resources.
• Data collected from problem solving is placed into an FMEA for future planning of new products or process quality. This allows an FMEA to consider actual failures, categorized as failure modes and causes, making the FMEA more effective and complete.
• The design or process controls in an FMEA are used in verifying the root cause and Permanent Corrective Action (PCA).
• The FMEA and Problem Solving reconcile each failure and cause by cross documenting failure modes, problem statements and possible causes.

FMEA Example

This FMEA Example has one item with a progression through multiple recommended Actions. With each instance, the revised RPN has improved. The final RPN of 10 indicates the issue has been mitigated successfully. The new state should be captured as Standard Work.

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