What Is FMEA
How FMEA is conducted
How to develop an FMEA
What Is FMEA
Failure Mode Effects Analysis (FMEA) is a structured approach to discovering potential failures that may exist within the design of a product or process. Failure modes are the ways in which a product or process
can fail. Effects are the ways that these failures can lead to waste, defects or harmful outcomes for the customer or operators. Failure Mode Effects Analysis is designed to identify, prioritize and limit and eliminate these
failure modes. FMEA is not a substitute for good engineering. Rather, it enhances good engineering by applying the knowledge and experience of a Cross Functional Team to review the design progress
of a product or process by assessing its risk of failure. There are two broad categories of FMEA, Design FMEA (DFMEA) and Process FMEA (PFMEA); there is also a Machinery FMEA view and a Software FMEA view.
How FMEA is conducted
Design FMEA (DFMEA) explores the possibility of product malfunctions, reduced product life, and safety and regulatory concerns derived from:
- Material Properties
- Interfaces with other components and/or systems
- Engineering Noise: environments, user profile, degradation, systems interactions
- Previous Campaigns
Process FMEA (PFMEA) discovers failure that impacts product quality, reduced reliability of the process, customer dissatisfaction, and safety or environmental hazards derived from:
- Human Factors
- Methods followed while processing
- Materials used
- Machines utilized
- Measurement systems impact on acceptance
- Environment Factors on process performance
The efficiency of an assembly line depends on how reliable the tooling and equipment was designed and built. Assume you have an assembly line with 10 machines. Each machine can function at a 90% uptime rate.
Each machine may fail at random times, or mutually exclusive from one another. The resulting reliability of the line with 10 machines at 0.9 (90%) reliability each is 35%. This means that some portion of the
assembly line could be down 65% of the time. Expand this principle to complex assembly operations where many more than 10 individual machines are needed to produce products. The reliability of the line would
be much worse. A critical piece of equipment would fail nearly every day. This is no way to run a profitable business.
Machinery Failure Mode Effects Analysis (MFMEA) will help identify weaknesses in the reliability of the critical equipment and tooling during machinery, equipment or tooling design. Improving the reliability
of the components of the machine has the net effect of higher reliability. When reliability cannot be improved further, the ability to replace worn parts in an expedited way is considered. An attempt to
anticipate failure and add design features which measure the amount of wear or predict when maintenance will be necessary is also beneficial. All of these items and more are addressed and discovered in a
How to develop an 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
With best results coming from DFMEA and PFMEA being conducted concurrently.
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:
2.Path 1 Development (Failure Modes - Criticality)
- 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
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)
3.Path 2 Development (Causes & Occurrences - Significance)
Path 2 Development – (Potential Causes and Prevention Controls through Occurrence Ranking)
Concurrent with Pathway 1 Process FMEA
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
4.Path 3 Development (Testing & DV Development - Annoyance)
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).
Concurrent with Pathway 2 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.
5.Action Priority & Assignment
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 can lead to poor team behavior. The columns completed are:
6.Actions Taken / Design Review
- Review Recommended Actions and update status (this is done at the end of each session and pathway)
- Assign Actions to appropriate personnel
- Assign action due dates
FMEA Actions are closed when counter measures have been taken and are successful at reducing risk, generally by occurrence reduction. 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.
7.Re-ranking Severity, Occurrence, Detection & 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. Key to the recalculation is the reduction in occurrence and potentially the reduction
in detection through earlier or more rigourous and robust control methods. Columns completed in Step 7:
- Re-ranked Severity
- Re-ranked Occurrence
- Re-ranked Detection
- Re-ranked RPN (this is not used as a method for reprioritising further action against a threshold value)
- Generate new Actions, repeating Step 5, until risk has been mitigated
- Comparison of initial severity, occurrence and detection and revised severity, occurrence and detection
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:
When completed, Actions move the risk from its current position in the Quality-One FMEA Criticality Matrix to a lower risk position.
- 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