Failure Mode and Effects Analysis (FMEA)

Author: Wang Shaoyin (Editor)
Publisher:
Publish Date: 2003-04-01
Features: From the FMEA tables before and after improvement (partial), it can be seen that the severity of failure mode "1" was high before improvement, followed by failure mode "3," and failure mode "2" was the lowest. After improving the top-ranked failure modes "1" and "3," the severity of failures completely changed, with the ranking of failure severities from highest to lowest becoming: "2," "3," and "1." If this example had already improved failure modes "1" and "3" without updating the FMEA table, it would overlook the issues and cause confusion.
II. When to Conduct FMEA Analysis
In principle, the FMEA method can be applied to reliability analysis and quality management improvement at any stage. It is particularly suitable for the following situations:
(1) To shorten manufacturing preparation time and eliminate repetitive process defects.
(2) During new product design, to thoroughly identify potential problem points and lay the foundation for subsequent design.
(3) When developing a product quality plan.
(4) When defects are frequently reported by customers but not detected internally in the company.
III. FMEA Implementation Process
To ensure the efficiency and effectiveness of FMEA implementation, it must be clearly defined in the quality assurance or reliability assurance plan regarding the stages and frequency of FMEA implementation. FMEA is a relatively large-scale systematic engineering project, and relying on a single person or department alone is unlikely to achieve the desired results. Generally, a cross-departmental team needs to be organized for implementation. The team should typically include members from the Quality Department, Design Department, Engineering Technology Department, and Manufacturing Department. Supporting members may involve the Procurement Department, Sales Department, and Material Control Department, among others.
The general process for implementing FMEA is as follows:
1. Pre-Implementation Preparation
(1) Collect customer requirements, types of actual failures, understand the design concept, and investigate usage conditions, manufacturing conditions, environmental conditions, and user habits.
(2) Determine the stage of FMEA analysis, i.e., decide whether to implement FMEA in the product planning, development, design, manufacturing, testing, or usage stage, and select the appropriate FMEA analysis form based on the stage.
(3) Determine the severity assessment table. Based on the determined FMEA analysis stage and product characteristics, establish evaluation tables for failure frequency, failure impact, and failure detection probability. When filling in the corresponding columns of the evaluation table with failure-related items, team members should strive for consistent evaluation standards and, in the end, reach a consensus through comprehensive discussion. After the FMEA analysis begins, the evaluation table can be adjusted based on actual conditions.
2. Implement FMEA
(1) Create a system reliability block diagram.
(2) To list as many failure modes of each component as possible, it is best to gather knowledgeable and experienced personnel and use brainstorming techniques.
(3) Analyze the impact, frequency, causes, and detection difficulty of each failure mode. During analysis, consider angles such as customer requirements, reliability, safety, environment, and operational steps.
3. Review and Evaluate Results
After completing the FMEA analysis, carefully review whether any failure modes are missed, whether the descriptions are accurate, and whether there are significant deviations or errors in the impact, frequency, causes, and detection difficulty of each failure mode. Make revisions and improvements based on actual conditions.
4. Implement Improvement Measures
After the review and evaluation, the improvement measures determined by FMEA for critical failure causes must be implemented. The effectiveness of the measures should be evaluated based on product and process performance, and the FMEA table should be dynamically updated as the effectiveness of the measures is confirmed.
Section III: FMEA Application Tables for Each Stage of the Quality Loop
The FMEA method is analyzed and improved in the form of tables, and the items and focus of the FMEA table vary at different stages. This section provides an analysis and introduction.
A. General FMEA Table
There is no mandatory standard for what a standard FMEA table should look like, and each company has its own characteristics in FMEA tables. However, the main items are generally the same. Table 1-10 is a general FMEA table (partial). The meanings of the items in the table are as follows:
1. Component
The lowest level that constitutes the product (system), such as parts or assemblies. When filling in the "Component" column, ensure that all components are at the same level. For example, if the first component is "Left Door," the second component cannot be "Screw" because their levels differ.
2. Function
The function of the component.
3. Failure Mode
The failure phenomenon or category of the component.
4. Failure Cause
The cause of the failure, which generally has several causes, and different causes may have different frequencies.
5. Failure Impact
The impact on the upper-level subsystem or system when the component experiences a specific failure, considering the impact on safety, reliability, environment, etc.
6. Detection Method
The current inspection method for the failure.
7. Occurrence Frequency
The likelihood and frequency of the specific failure mode occurring.
8. Risk Assessment
The value obtained after assessing the occurrence frequency, impact, and detection method of the specific failure mode. Risk assessment helps determine the priority for improvement.
9. Countermeasure
The corresponding measures taken for the specific failure mode. When determining countermeasures, factors such as effectiveness, cost, risk, and time must be comprehensively considered. Countermeasures may involve:
(1) Taking measures to reduce the occurrence frequency of the specific failure mode.
(2) Taking measures to reduce the impact of the specific failure mode.
B. Design and Development Stage FMEA Table
The purpose of implementing FMEA during product design and development is to identify reliability and safety issues related to the product design. To determine important failure modes, the "severity" assessment is generally used instead of "risk" evaluation.
1. Differences Between "Severity" and "Risk"
"Severity" and "Risk" are two different concepts. "Risk" includes the assessment of failure detection probability, while "Severity" does not. The formulas are as follows:
Severity = Failure Occurrence Frequency × Failure Impact
Risk = Failure Occurrence Frequency × Failure Impact × Detection Probability
During the product design stage, the focus is on the frequency of failure occurrence and its impact on the system, users, and environment. Detection probability is more considered during process design, so the "severity" is used in design stage FMEA to evaluate the destructive power of a specific failure.