Failure Mode and Effects Analysis (FMEA) is an integral part of product and process design activity. The FMEA process is applicable in Design of Products, Processes and Services. FMEA is a universal tool that is used in any industry or service, where risk of failure has detrimental effects on the users of a product, process or service. The primary reason for performing a FMEA is taking action to prevent a failure, improve a design control through testing or evaluation, or a process control through inspection. In a FMEA, risk is the substitute for failure. This risk is treated as if the failure had already occurred and corrective action is required.
FMEA is an analytical methodology used to ensure that potential problems have been considered and addressed throughout the product and process development cycle. FMEA helps to:
- Discover the potential failures, their potential cause mechanisms and the risks designed into a product or process
- Develop actions that reduce the risk of failure
- Follow-up and evaluate the results of actions on the risks that were discovered
A Design FMEA (DFMEA) is performed prior to the completion of the design of the product. A Process FMEA (PFMEA) is performed prior to the release of the design for the process. PFMEAs should ideally be conducted when DFMEAs provide special characteristics or when new process technology is planned. It is critical that a FMEA be performed with sufficient time to take counter measures against the risk and still capture the changes within the design before its release. Quality-One FMEA Training and FMEA Facilitation techniques are the “Best-in-Class” and provide a great understanding about how a FMEA works.
FMEAs are conducted by a core team of three or four people with supporting Subject Matter Experts (SME). This group creates the Cross Functional Team (CFT). Ideally, the CFT should be selected from disciplines that have a slightly different view of the product or process under investigation. The synergy created by the CFT is what makes FMEA so powerful.
A single person will not be able to develop a comprehensive FMEA without input from the CFT. It is easy to tell when a FMEA is created by one individual rather than the team. Such FMEAs are typically generated to satisfy customer requirements but have very little value to the program or organization. FMEAs are a means to achieve better quality products and processes. Many Original Equipment Manufacturers (OEMs) require the proper use of FMEA. Industry standards in diverse industries, such as automotive, medical device manufacturing, aerospace, chemical processing and more, have been developed to utilize the power of FMEA.
There are 7 Steps to Developing a FMEA:
- FMEA Pre-Work
- Path 1 Development (Failure Modes)
- Path 2 Development (Causes & Occurrences)
- Path 3 Development (Testing & DV Development)
- Action Priority & Assignment
- Actions Taken / Design Review
- Re-ranking RPN & Closure
1. FMEA Pre-Work
To ensure the FMEA will work smoothly through the development phases, an investigation of past failures and preparatory documents is required. Preparatory documents may include:
- Failure Mode Avoidance (FMA)
- Boundary/Block Diagram (For the DFMEA)
- Parameter Diagram (For the DFMEA)
- Process Flow Diagram (For the PFMEA)
The purpose of Pre-Work is to create a list of:
- Known causes from surrogate products
- Potential causes from interfaces
- Potential causes from design choices
- Potential causes from noises and environments
- 6 M’s / Fishbone list of potential causes from past FMEAs and Eight Disciplines of Problem Solving (8D)
2. Path 1 Development (Failure Modes)
Path 1 consists of inserting the Functions, Failure Modes, Effects of Failure and Severity Rankings. The Pre-Work documents assist in this task by simply taking information previously captured to populate the first 4 to 7 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 Anti-Functions; 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.
3. Path 2 Development (Causes & Occurrences)
Causes are selected from the Boundary Diagram, Parameter Diagram, or past failures and placed in the Cause column when applicable to a specific failure mode.
The columns completed in Path 2 are:
- Causes from ION or 6M’s
- Preventions from Standard Work and previously successful designs
- 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 Q-1 Criticality Matrix.
4. Path 3 Development (Testing & DV Development)
Path 3 Development involves the addition of Detection Controls to prevent a design flaw (for Design FMEA) or Cause and/or a Failure Mode that may reach a customer (for Process FMEA).
The columns completed in Path 3 are:
- Detection Controls
- Detection Ranking
Actions are taken to improve the controls if they are insufficient to the risks determined in Paths 1 and 2.
5. 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.
Columns in Action Priority include:
- Verification of Actions captured in Paths 1, 2 and 3
- RPN Values
- Responsibility and Timing to clarify who is responsible for the Action and when the Action is expected to be completed
6. Actions Taken / Design Review
Actions indicated from the FMEA analysis are closed through the collection of data and observations after a counter measure has been taken. 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 RPN & 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 Old RPN is compared to the new RPN and the relative improvement made 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
The RPN is often used to determine the relative risk of a FMEA line item. In the past, RPN has been used to determine when to take action. RPN should not be used this way. Quality-One recommends never using RPN for action determination.
Actions are determined by Criticality. Criticality is the combination of Severity and Occurrence, as displayed in the Q-1 Criticality Matrix.
The actions, when completed, move the risk from its current position in the Q-1 Criticality Matrix to a lower risk position. Items with the greatest risk are based on Severity of the Effect combined with the likelihood of Occurrence in a specific Cause. When risk is determined to be too high, Q-1 recommends the priority of action to be applied as follows:
- 1.Error Proofing
- a. Failure Mode (Only Severity of 9 or 10)
- b. Cause with High Occurrences
- 2.Improve Potential Process Capability
- a. Increase Tolerance (Tolerance Design)
- b. Reduce Variation of the Process (Statistical Process Control and Process Capability)
- 3.Control Plan Methodology (Improve Controls)
- a. Mistake Proofing of the Tooling or Process
- b. Improve the Inspection and Evaluation Techniques
Failure Mode and Effects Analysis from Quality-One; Discover the Value!