Six Sigma Charts

Introduction to Failure Modes and Effects Analysis (FMEA)

FMEA is a design tool for assessing risk associated with the different ways or modes in which a part or system can fail.
FMEA help identify the effects of those failures by the inductive reasoning process
FMEA provides a structured methodology to review and archive changes
FMEA allow for a quantitative analysis of risk
FMEA charts are useful tools for comparing two or more design concepts

How does Failure Mode establish the relation between Cause and Effect? The Effects or Symptoms of a Problem are usually the very first thing we can readily identify. Once the effects are established we can work backwards to identify the Cause and Zero-in the actual Mode or way in which the failure actually happened.

The tables below exemplify the use of the FMEA method to analyze, address and archive the improvement efforts made to the headlight circuit assembly of a vehicle.

(Jan 2018) FMEA: Car Headlight Failures
Product Function Requirements	Failure Mode	Effects	S	Root Cause	O	Current Controls	D	Risk Priority Number
Headlights aid on night driving	Headlights won't turn on	Car inoperable at night	10	Battery Dead	8	Keep Lights off	6	480
				Broken wire	8	Check continuity	3	180
				Headlight Out	10	Visual inspection	2	200
				Switch corroded	2	Check continuity	6	120
				Switch broken	3	Check continuity	6	180
Corrective Action: Actions or corrective measures to be taken (i.e. Add a second Headlight and a Dashboard indicator) Assign individuals to implement these measures (Engineer 1) Assign completion deadlines.
Action Results: Record how the corrections were accomplished and what was learned along the way Recalculate Severity (S), Occurrence (0), Detectability (D), Criticality and PRN numbers in a new chart Re- start the FMEA process until all Criticality and PRN are at their minimum possible value.
The table below is a revision of the table above:

(Feb 2018) FMEA: Car Headlight Failures
Product Function Requirements	Failure Mode	Effects	S	Root Cause	O	Current Controls	D	Risk Priority Number
Headlights aid on night driving	Headlights won't turn on	Car inoperable at night	10	Battery Dead	8	Keep Lights off	4	320
				Broken wire	8	Check indicator	2	160
				Headlight Out	10	Check indicator	1	100
				Switch corroded	2	Check continuity	6	120
				Switch broken	3	Check continuity	6	180
Corrective Action: Actions or corrective measures to be taken Assign individuals to implement these measures Assign completion deadlines.
Action Results: Record how the corrections were accomplished and what was learned along the way Recalculate Severity (S), Occurrence (0), Detectability (D), Criticality and PRN numbers in a new chart Re- start the FMEA process until all Criticality and PRN are at their minimum possible value.
The table below shows how to assign Severity (S) values:

Criteria for Severity (S) Ranking	Effect	Rank
Failure occurs without warning	Deadly	10
Failure occurs with warning	Hazardous	9
Product is inoperable, total loss of function	Very Serious	8
Product is operable, but with loss of performance	Serious	7
Product is operable, but with loss of comfort	Moderate	6
Product is operable, but with low effect on performance	Low	5
Noticeable effect by most customers	Very Low	4
Noticeable effect by average customers	Minor	3
Noticeable effect by discriminating customers	Very Minor	2
No effect	None	1
The table below shows how to assign Probability of Occurrence (O) values:

Criteria for Probability of Occurrence (O) Ranking
Occurrence	Failure Rate	Criteria	Rank
Very High	>1 in 2	Failure is almost inevitable	10
Very High	1 in 3	Failure is almost inevitable	9
High	1 in 8	Repeated Failures	8
High	1 in 20	Repeated Failures	7
Moderate	1 in 80	Occasional Failures	6
	1 in 400		5
	1 in 2,000		4
Low	1 in 15,000	Relatively few failures	3
Low	1 in 150,000	Relatively few failures	2
Remote	<1 in 1,500,000	Failure is Unlikely	1
The table below shows how to assign Detectability (D) values:

Criteria for Detectability (D) Ranking
Chances of Detection of Failure Mode	Rank
No known controls available	10
Very remote chances of detection	9
Remote chances of detection	8
Very low chances of detection	7
Low chances of detection	6
Moderate chances of detection	5
Moderately High chances of detection	4
High chances of detection	3
Very High chances of detection	2
Almost certain to detect	1