How to Use PFMEA ?
Process Failure Mode and Effects Analysis
  • What is PFMEA ?

PFMEA is the abbreviation of Process Failure Mode and Effects Analysis (Process Failure Mode and Effects Analysis). The mechanism has been fully considered and discussed.

Failure: Under the specified conditions (environment, operation, time), the established function or product parameter value cannot be completed and cannot be maintained between the specified upper and lower limits, and the components are broken and stuck within the working range and other damage phenomena.

Severity (S): Refers to the level of the most severe impact consequence for a given failure mode, and is a relative rating result within the scope of a single FMEA. Reductions in severity numbers can only be achieved through design changes or redesigns.

Frequency (O): Refers to the possible occurrence of a specific cause/mechanism, and the number of levels describing the possibility of occurrence has relative significance, but not absolute.

Detectability (D): refers to the evaluation index of the possibility of using the second current process control method to find out the failure cause/mechanism process defect or the subsequent failure mode before the part leaves the manufacturing process or assembly; Three process control methods evaluate the likelihood of finding subsequent failure modes.

Risk Priority Number (RPN): refers to the product of the severity (S), the frequency (O) and the difficulty in detection (D).

Customer: Generally referred to as the "end user," but can also be subsequent or downstream manufacturing or assembly operations, maintenance operations, or government regulations.

  • Scope of application

New part mold design stage.

New parts trial mode, trial production stage.

The new parts enter the pre-production stage.

New item customer complaint stage.

  • Principle analysis

Analysis principle of PFMEA

The analysis principle of PFMEA is shown in the following table. It includes the following key steps: (1) Identify potential failure modes and causes related to process production or product manufacturing process;

(2) Evaluate the potential impact of failure on product quality and customers;

(3) Identify process control variables that reduce failure occurrence or failure conditions, and develop corrective and preventive actions;

(4) Prepare a potential failure mode classification table to ensure that serious failure modes are prioritized for control;

(5) Track the implementation of control measures and update the failure mode classification table.

  • Pattern analysis

"Process Function/Requirement"

Refers to the process or process being analyzed. The process or process can be a technical process, such as welding, product design, software coding, etc., or a management process, such as planning, design review, etc. Describe the purpose of the process or procedure as simply as possible, and if the process includes many procedures with different failure modes, these procedures or requirements may be listed as separate procedures;

"Potential Failure Mode"

Refers to the form or problem point that may occur in the process that does not meet the process requirements or design intent, and is a description of a specific process that does not meet the requirements. It can be a potential failure mode that causes the next process, or it can be a consequence of a previous process failure mode. Typical failure modes include fracture, deformation, improper installation and debugging, etc.;

"Failure Consequences"

It refers to the possible adverse effects of failure mode on product quality and customers. The failure consequences are described according to the conditions that customers may notice or experience. For end users, the consequences of failure should always be described in terms of product or system performance. Such as noise, odor, no effect, etc.;


It is the severity of the impact of the potential failure mode on the customer. In order to accurately define the adverse effect of the failure mode, it is usually necessary to evaluate the potential impact of each failure mode and assign a score, expressed as 1-10 points, the higher the score, the higher the The more serious the impact. "Possibility": It refers to the probability of a specific failure cause. The grading number of the possibility focuses on its meaning rather than the value. Usually, 1-10 points are used to evaluate the possibility. The higher the score, the better the chance. big. "Difficulty to detect": refers to the degree of difficulty in discovering defects in the process of failure before the parts leave the manufacturing process or equipment station. The evaluation index is also divided into 1-10 levels. out;

"Cause/Mechanism of Failure"

Refers to how the failure occurred, and is described in terms of principles that can be corrected or controlled. For each potential failure mode, list every conceivable failure cause in the widest possible range, if the cause is relevant to the failure mode. Said to be unique, then the consideration process is complete. Otherwise, it is necessary to analyze the root cause among the many causes, so that corrective measures can be taken for those related factors. Typical failure causes include: incorrect welding, improper lubrication, wrong parts, etc.;

"Current Control Method"

is a description of the control methods currently in use to prevent failure modes as much as possible or to detect failure modes that will occur. These control methods can be physical process control methods, such as the use of error proof fixtures, or administrative process control methods, such as the use of statistical process control (SPC) techniques;

"Risk Level (RPN)"

is the product of severity, likelihood, and undetectability. The higher the value, the more serious the underlying problem, and the sooner corrective action should be taken in an effort to reduce the value. In general, regardless of the value of the risk level, special attention should be paid when the severity is high;

"Recommended Action"

It is a response plan developed to reduce the severity, likelihood or undetectable value of a risk, including action plans or measures, responsible persons, resources that may be required, and completion dates. When the failure modes are prioritized, corrective actions should be taken first for the highest risk event or event with high severity. The purpose of any suggested action is to prevent its occurrence, or reduce the impact and loss after it occurs;

"Results of Measures"

It is the tracking and confirmation of the implementation status of the above-mentioned "recommended measures" plan. After the corrective measures are identified, re-estimate and record the severity, likelihood and undetectable values ​​after the corrective measures are taken, and calculate and record the new risk level value after correction, which should be higher than the risk level value before the result of the measures. is much lower, thus indicating that the risk of failure can be sufficiently reduced by taking measures.

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