FMEA failure mode and effect analysis professional third-party testing service organization

Date：2022-05-17 15:22:59Views：781

FMEA failure mode and effect analysis. FMEA failure mode and effect analysis is an "ex ante behavior" rather than an "ex post behavior". In order to achieve the best benefit, FMEA must be carried out before the failure mode is incorporated into the product.

Since product failures may be related to design, manufacturing process, use, contractors / suppliers and services, FMEA is divided into four categories: Design FMEA, Process FMEA, use FMEA and service FMEA. Among them, Design FMEA and Process FMEA are the most commonly used.

FMEA can also be called potential failure mode and Effect Criticality Analysis. Early FMEA was only a qualitative method in reliability analysis. It was applied in the field of aviation and aerospace to study various potential failure modes and their effects on product functions. Later, it was extended to product performance analysis and analysis of manufacturing process and service process. In the late 1990s, FMEA has been introduced into the quality management system in the automobile, motor, electrical and other industries, among which the automobile industry also takes it as one of the five manuals of the quality system (QS9000). As a preventive technology, FMEA can reduce or eliminate greater losses caused by design defects and ensure the safety of products to the greatest extent in high-risk fields such as military industry, aviation and nuclear industry.

Before introducing FMEA in more depth, explain some words.

*Failure: refers to the state in which the product loses the specified function, which can also be translated as failure. The meaning of failure and failure is slightly different. Failure is for irreparable products; The fault is for Repairable Products. Failure here contains these two meanings.

*Failure mode: refers to the manifestation of product failure, such as material bending, fracture, part deformation, improper equipment installation, etc.

*Potential failure mode: refers to the failure mode that can occur but does not necessarily occur. At this time, the engineering and technical personnel recognize or feel the possible hidden dangers in the process of design, manufacturing and assembly.

*Effect analysis: refers to the criticality that a failure mode will bring to customers if it occurs. The criticality in FMEA includes three meanings and is legally quantified. These three layers mean:

a) Severity of the consequences of a failure mode;

b) Frequency of occurrence of the cause of a failure mode;

c) The degree of undetectable failure.

The severity of failure consequences is usually described by grading. The severity is divided into 10 levels, 10 points for the most serious and 1 point for no impact.

Calculate the number of prior risks (RPN)

The risk priority number is the product of severity (s), frequency (o) and imperceptible measure (d), i.e. RPN = (s) × （O） × （D）

The size of RPN is to sort the concerns in the process. High RPN failure modes mean great risks. Experts and engineers must pay enough attention to these failure modes, take corrective and preventive measures, and strive to reduce the value of RPN.

After knowing the RPN value, first put forward corrective and preventive measures for the top things and the most critical failure modes to reduce the failure risk. If the root cause of failure is unknown, the main cause shall be determined through test design and other means. Without correct and effective corrective measures, the value of FMEA work is limited. Generally speaking, it is uneconomical to improve the measurement and control ability to reduce RPN, and the effect is poor. Increasing the number of quality inspections is not a positive corrective measure. Permanent corrective measures are necessary. Therefore, in some cases, the design should be changed, even the design of the current control system. The focus should be on reducing the frequency of failure modes rather than trying to detect them.

The progress of corrective and preventive measures shall be tracked and verified in time. The verification method is a new round of risk assessment - reassess the severity (s), frequency (o) and difficult to detect measure (d) of failure mode, and recalculate the number of prior risks (RPN).

Corrective and preventive measures are often impossible to succeed at one time, and need continuous improvement and verification. FMEA will end only when severity (s) and prior risk number (RPN) are significantly reduced to satisfaction.