Failure Mode & Effect Analysis - Tool

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Failure Mode & Effect Analysis

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Failure Mode and Effects Analysis (FMEA)

FMEA is a structured analysis for identifying ways & methods in which the product or processes can fail and then plan to prevent those failures. FMEA is a proactive tool for reducing defects and nonconformities.

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FMEA

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FMEA is a structured approach in :Identifying ways in which a product / process can fail to meet critical customer requirements. Estimating the risk of causes with regard to these failures. Evaluating control plan for preventing these failures. Prioritizing the actions for improving the process. FMEA is an extremely important tool for each phase of Six Sigma strategy viz. Measure, Analyze, Improve, Control.

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Advantages of FMEA

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For improving the reliability and safety of the products.

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For improving customer satisfaction.

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Tracking actions to reduce non-conformities.

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New product development.

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Definition of terms

Failure Mode : It is a manner in which a part or a process can fail to meet specifications. It is usually associated with defect or non-conformities. Examples : Missing part, Oversized, Undersized, Incorrect price, Offspec parts.

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Definition of terms

Cause : Causes are sources of variation which are associated with key process inputs. Cause can be best defined as a deficiency which results in a failure mode. Examples : Instructions not followed, Lack of experience, Incorrect documentation, Poor handling etc.

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Definition of terms

Effect : Effect is the impact on the customer (both internal & external) if the failure mode is not prevented or corrected. Examples : Customer dissatisfaction, Frequent product breakdowns, Customer downtime.

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Relationship of cause, failure mode & effect

Cause

Failure Mode

Effect

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FMEA through Cause & Effect Diagram Causes

Causes

Causes

Prevent or Detect

Failure Mode

Effect

Causes

Causes

Causes

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Steps in FMEA process

1. Develop a process map and identify process steps. 2. List key process outputs for satisfying internal and external customer requirements. 3. List key process inputs for each process steps. 4. List ways the process inputs can vary (causes) and identify associated failure modes and effects. 5. Assign severity occurrence and detection rating for each cause.

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Steps in FMEA process…contd.

6. Calculate risk priority number ( RPN) for each potential failure mode. 7. Determine recommended actions to reduce RPN’s. 8. Establish time frame for corrective actions. 9. Take corrective actions. 10. Put all controls in place.

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Ranking terms used in FMEA calculations Scale:1(Best) to 10 ( Worst)

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Severity (SEV) : Severity indicates how severe is the impact of the effect on the customer.

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Occurrence (OCC) : This indicates the likelihood of the cause of the failure mode to occur.

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Detection (DET) : This indicates the likelihood of the current system to detect the cause or failure mode if it occurs.

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Risk priority number : This number is used to place priority to items for better quality planning. RPN = SEV X OCC X DET

See next slides for specimen best to worst ratings on a 10 point scale.

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Best to Worst ratings for FMEA calculations Rating

Degree of Severity

Likelihood of Occurrence

Ability to detect

1

Customer will not at all observe the adverse effect

Very remote possibility

Sure that the potential failure will be detected & prevented before reaching the next customer

2

Customer will experience slight discomfort

Low failure with supporting documents

Almost sure that the potential failure will be detected before reachig the next customer

3

Customer will experience annoyance because of slight degradation of performance

Low failure without supporting documents

Less chances that the potential failure will reach the next customer undetected

4

Customer dissatisfied due to reduced performance

Occasional failures

Some controls may detect the potential from reaching the next customer

5

Customer is uncomfortable

Moderate failure rate with supporting documents

Moderate chances that the potential failure will reach the next customer

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Best to Worst ratings for FMEA calculations Rating

Degree of Severity

Likelihood of Occurrence

Ability to detect

6

Warranty repairs

Modearate failure rate without supporting documents

Controls are not likely to detect or prevent the potential failure from reaching the next customer

7

High degree of customer dissatisfaction

High failure rate with supporting documents

Less chances that the potential failure will be detected or prevented before reaching the next customer

8

Vey high degree of customer dissatisfaction

High failure rate with supporting documents

Very less chances that the potential failure will be detected or prevented before reaching the next customer

9

Negative impact on the customer

Failure is almost certain

Existing controls will not detect the potential failure

10

Negative impact on the customer, people & society

Assured failure

Existing controls will not detect the potential failure

FMEA Form: ( Column 1 to 9 )

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Rank severity on 1 to 10 scale

1 Process Part No.

Rank occurrence on a 1 to 10 scale

2 3 Potential failure mode Potential failure effect

Rank how well cause/failure can be detected on 1 to 10 scale

List how the cause is presently being controlled

4 SEV

5 Potential causes

6 OCC

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7 Current Controls

8 DET

9 RPN

1 2 3 4 5

List failure modes for each step

List effects of each failure mode

List causes for each failure mode

RPN= SEV*OCC*DET

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FMEA Form contd: ( column 10 to 15 ) Designates people responsible for corrective action

10 11 Actions Recommended Responsibility

List actions recommended on RPN pareto

RPN is recalculated on completion of corrective action

12 SEV

13 OCC

14 DET

15 RPN