Quality and Standards: Preventing Problems
April 20, 2009
There are many reasons why successful appliance design manufacturers use Failure Mode and Effects Analysis (FMEA), including lower warranty costs, more successful testing programs, improved safety and compliance. But one of the most important reasons to use FMEA during appliance design is customer satisfaction. Nothing causes a customer to turn against a company’s products faster than appliance failures, and nothing generates better customer loyalty than robust trouble-free appliances.
FMEAs done effectively during the appliance design process will discover potential problems, prioritize the risk, and provide effective solutions to reduce or eliminate risk.
Understanding why FMEAs are important begins with the Product Development Process and the tools that support Design for Reliability. Today’s corporations are facing unprecedented worldwide competition as a result of three continuing challenges: The mandate to reduce costs, faster development times, and high customer expectations for the reliability of products and processes. The necessity for Reliability Testing is still important. However, there is increasing emphasis on Design for Reliability as a corporate strategy.
We’ve all heard the maxim: pay now, or pay a lot more later. If reliability cannot fit in the current budget, then where does one find a place in the budget for fixing field issues, field recalls, and lost customers?
The key is to discover potential problems as early as possible in the design process. It is far less expensive to fix a problem before designs are frozen and manufacturing tooling has begun. Late design changes, lengthy test-and-fix programs, and field changes can all be very expensive. For this reason, one of the most effective reliability strategies is FMEA.
Once a company decides to use FMEA as part of a reliability program, some obvious questions arise. How does a design team perform an FMEA? What’s the difference between an effective and ineffective FMEA? How can practitioners ensure FMEAs are performed to achieve the desired results?
FundamentalsFMEA is a methodology designed to identify and fully understand potential failure modes for a product or process, assess the risk associated with those failure modes, prioritize issues for corrective action, and identify and carry out corrective actions to address the most serious concerns. Teams and team leaders must be trained in the procedure.
There are three major types of FMEAs and many other subtypes:
- System FMEA is the highest level analysis of the entire system, including the interfaces and integration.
- Design FMEA focuses on design related issues typically at the subsystem or component level.
- Process FMEA focuses on process related issues for the manufacturing or assembly process.
The first step is to assemble the correct Design FMEA Team, which usually consists of experts on the system and its design, along with representatives from quality/reliability, manufacturing, testing, and service. This cross-functional team is essential to ensure that the designs are free of potential failures and meet or exceed all reliability requirements. These people should be well trained in the FMEA procedure.
It is also important to use good software to support FMEA development and documentation. Relational database software, such as ReliaSoft’s Xfmea, is recommended in order for the team to have easy and instant access to the entire database of FMEAs, field history, linkage to test plans, and full-featured search and reporting capabilities.
The next step is to define the FMEA scope, identifying which aspects will be addressed: systems, subsystems, components, interfaces, electrical features, mechanical features, and in-house vs. outside supplier sourcing. Ideally the scope is represented as a visual diagram called an FMEA Functional Diagram.
Other preparation items include previous FMEAs on similar systems, a list of field failures from similar systems, agreement on the assumptions going into the FMEA, design specifications, and current test plans.
Definitions for common FMEA terms include:
- Function: What task the item is intended to perform, usually to a given standard of performance.
- Failure Mode: The way the part or assembly could fail to meet requirements.
- Effect: The consequence of the failure on the next higher subsystem, system, or user.
- Cause: The reason for the failure, preferably found by asking “why” until the root cause is determined.
- Control: The method or action currently in place to reduce risk.
- Risk Priority Number (RPN): A numerical ranking of the risk of each potential failure mode, which is comprised of three elements: severity of the effect, occurrence of the cause, and detection of the cause.
- Recommended Actions: The specific action steps that will be implemented to reduce risk to an acceptable level.
ProcedureFor each item that will be analyzed, identify its functions, failures, effects, causes, and current controls. Use engineering and business judgment to select the issues that will be considered in the analysis.
Rate the severity of the effect on the appropriate severity scale. Rate the likelihood of occurrence of the cause on the appropriate occurrence scale. Rate the likelihood of detection of the cause (based on current controls) on the appropriate detection scale. Multiply the three rankings together to get the risk priority number (RPN) for each failure mode being considered.
Develop effective recommended actions to reduce risk to an acceptable level, based on RPN priorities and high severity.
StandardsThere are many published FMEA Standards. The SAE J1739 FMEA Standard is recommended and available on the SAE Web site. Although this standard is published under the Society of Automotive Engineers, it has many years of success in other applications. The scales should be tailored to a specific company application. Quality standards supported by ISO and Europe often include mention of FMEAs or risk management. Without going into detail of each standard, in general, experience has demonstrated that well done FMEAs are consistent with ISO and European quality standards.
LessonsLearning the FMEA procedure is not enough to be a successful practitioner. Performing successful FMEAs requires understanding and implementing the key factors for effective FMEAs, the quality objectives. The primary ways that FMEA can be incorrectly performed are the mistakes. There is a maxim: good judgment comes from experience and experience comes from poor judgment. Here are some examples of lessons learned and resulting quality objectives.
- 1. Based on empirical review of many FMEAs, some of them do not drive any action at all; some drive mostly testing; others drive ineffective action. The lesson learned: failure of the FMEA to drive design or process improvements. The quality objective: the Design FMEA drives product design improvements as the primary objective.
2. Failure to address all high risk failure modes (including high severity) can result in potentially catastrophic problems or lower customer satisfaction. The lesson learned: failure of the FMEA to address all high risk failure modes. The quality objective: the FMEA addresses all high risk failure modes, as identified by the FMEA team, with effective and executable action plans.
3. Some companies miss the opportunity to improve Test Plans based on the failure modes/causes from the FMEA. Some FMEA teams do not include knowledgeable representatives from the test department. The lesson learned is: failure of the FMEA to improve test plans. The quality objective: the test plan considers the failure modes from the FMEA.
4. Empirical data shows that at least 50 percent of field problems can occur at interfaces or integration with the system. The lesson learned is: not including interfaces or integration in FMEA. The quality objective: the FMEA scope includes integration and interface failure modes in both block diagram and analysis.
5. Some companies provide no linkage between FMEAs and field data. This can cause serious problems to repeat. The lesson learned is: disconnect between FMEA and field lessons learned. The quality objective: the FMEA considers all major lessons learned (such as high warranty, campaigns, etc.) as input to failure mode identification.
6. Many companies have a key characteristics policy. The design FMEA can identify key product characteristics for special controls in manufacturing. The lesson learned is: FMEA omitted key characteristics. The quality objective: the FMEA identifies appropriate key characteristics candidates, if applicable according to company policy.
7. Many companies do FMEAs late, and this reduces their effectiveness. FMEAs should be completed by design or process freeze dates, concurrent with the design process. The lesson learned is: doing FMEAs late reduces effectiveness. The quality objective: the FMEA is completed during the “window of opportunity” where it can most effectively impact the product or process design.
8. Some FMEA teams do not have the right experts on the core team. Some FMEA teams do not have good attendance. The lesson learned is: FMEAs with inadequate team composition. The quality objective: the right people participate on the FMEA team throughout the analysis, and are adequately trained in the procedure.
9. There are hundreds of ways to do FMEAs wrong. Some companies do not encourage or control proper FMEA methodology. The lesson learned is: FMEAs with improper procedure. The quality objective: the FMEA document is completely filled out “by the book,” including “action taken” and final risk assessment.
10. Some companies mandate FMEAs and then do not ensure the expert’s time is well spent. The lesson learned is: lack of efficient use of time. The quality objective: The time spent by the FMEA team, as early as possible, is an effective and efficient use of time with a value added result.
Furthermore, the importance of broad support from management in implementing an effective FMEA process cannot be overstated. Without strong support, organization-wide FMEA implementation will often fail or languish. There need to be enablers in place, and positive management support must achieve the following:
- Provide positive direction to engineers.
- Provide agreement on strategy and support needed resources such as training, software, standards, etc.
- Assist in integrating FMEA with other business processes such as design reviews, supplier controls, quality audits, test plans, test and field results, etc.
- Provide effective reviews of higher risk failure modes and recommended actions.
- Provide attendance of expert FMEA team members.
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