Failure Mode Effect Analysis-APR132K7

APPLICATION OF FMEA TO THE DESIGN OF A COOLING FAN ASSEMBLY POTENTIAL EFFECT(S) OF FAILURE Audible noise vibration; increased motor wear

S 5

Motor burnout, bearing or brush failure

Loss of cooling and A/C function

5

Motor: provide Mechanical Power to fans; Position fans Within shroud

Misassemble to shroud, off center or crooked

Loss of cooling function

Motor: provide Mechanical Power to fans; Position fans Within shroud

Assemble at ±12o offnominal Angle, motor wire in Wrong location

No-build condition in assembly plant

PART NAME AND PART FUNCTION

POTENTIAL FAILURE MODE

Motor: provide Mechanical Power to fans; Position fans Within shroud

Fan vibration from imbalance and axial TIR

Motor: provide Mechanical Power to fans; Position fans Within shroud

7

6

POTENTIAL CAUSE(S) OF FAILURE Fan’s centre of gravity off axis of rotation; axial TIR Causes 2-plane imbalance

Overheating, lack of air circulation

Fan contact, shroud, noise, or motorburn-out

Symmetrical spacing of screw holes; non-unique mounting interfaces

O 5

2

2

6

DESIGN VERIFICATION • Design lightweight fan with min. band mass; part thickness to favour uniform mould flow • DV tests on vehicles to assess sensitivity to vibration inputs Vent holes in motor case; fins in fan hub pull air through ES, durability tests

Design for easy assembly, accurate positioning in shroud

• Power motion motor has unique mounting configuration • Visual inspection during assembly

D 4

RPN 100

5

50

3

42

3

108

THIS TABLE SHOWS THE STANDARD FMEA FORMAT USED IN THE DESIGN OF A COOLING FAN ASSEMBLY USED IN THE AIRCONDITIONING UNITS FOR AUTOMOTIVE VEHICLES. THE FIRST COLUMN IN THE TABLE IS FOR THE PART NAME AND PART FUNCTION. THE PART CONSIDERED IN THIS EXAMPLE IS THE MOTOR WHICH PROVIDES MECHANICAL POWER TO THE FAN. THE SECOND COLUMN REQUIRES INFORMATION ABOUT THE POTENTIAL FAILURE MODES. IN CASE OF THE MOTOR, THE FIRST POTENTIAL FAILURE MODE IS MENTIONED AS FAN VIBRATION FROM IMBALANCE.

THE THIRD COLUMN REQUIRES THE POTENTIAL EFFECTS OF THE FAILURE WHICH, FOR FAN VIBRATION, HAS BEEN MENTIONED AS AUDIBLE NOISE VIBRATION AND INCREASED MOTOR WEAR. THE SEVERITY RATING (S) IS FOUND QUALITATIVELY FROM FOLLOWING TABLE:

QUALITATIVE SCALE FOR THE SEVERITY INDEX (S) Effect

Level

Criteria

Non

1

No effect

Very slight

2

Customer not annoyed. Very slight effect on product or system performance.

Slight

3

Customer slightly annoyed. Slight effect on product or system performance.

Minor

4

Customer experiences minor nuisance. Minor effect on product or system performance.

Moderate

5

Customer experiences some dissatisfaction. Moderate effect on product or system performance.

Significant

6

Customer experiences discomfort. Product performance degraded, but operable and safe. Partial failure, but operable.

Major

7

Customer dissatisfied. Product inoperable but safe. System inoperable.

Extreme

8

Customer very dissatisfied. Product inoperable but safe. System inoperable.

Serious

9

Potential hazardous effect. Able to stop product without mishap – time dependent failure. Compliance with government regulation is in jeopardy.

Hazardous

10

Hazardous effect. Safety related sudden failure. Non-compliance with government regulation.

THE NEXT COLUMN IN THE TABLE IS THE POTENTIAL CAUSES OF THE FAILURE, WHICH HAS BEEN IDENTIFIED AS THE FAN’S CENTER OF GRAVITY, WHICH IS OFF THE AXIS OF ROTATION. THE NEXT COLUMN IS FOR THE FREQUENCY OF OCCURRENCE (O) OF THE FAILURE MODE. THE NEXT COLUMN IS FOR DESIGN VERIFICATION. FOR FAN VIBRATION, IT IS ‘DESIGN LIGHTWEIGHT FAN WITH MINIMUM BAND MASS’. IT ALSO SUGGESTS A TEST ON VEHICLES HAVING THE AIR CONDITIONING UNIT INSTALLED FOR ASSESSING SENSITIVITY TO VIBRATION INPUTS. THE SECOND LAST COLUMN IS FOR THE DELECTABILITY INDEX (D) WHICH QUALITATIVELY MEASURES HOW EASY IT IS TO DETECT A FAILURE MODE. IN CASE OF FAN VIBRATION, IT HAS BEEN TAKEN FROM TABLE AS 4, WHICH IS MODERATELY HIGH ON THE CRITERIA OF TESTS ON EARLY PROTOTYPE SYSTEM ELEMENTS. THE LAST COLUMN IN TABLE IS FOR RISK PRIORITY NUMBER (RPN) WHICH IS CALCULATED BY USING THE FOLLOWING FORMULA:

RPN  S  O  D

THUS, RPN HELPS IN PRIORITIZING THE FAILURE MODES AND WORKING OUT FOR THEIR PREVENTION. IN CASE OF FAN VIBRATION, THE RPN HAS BEEN CALCULATED AS

RPN  5  5  4  100 QUALITATIVE SCALE FOR THE OCCURRENCE INDEX (O) Effect

Level

Criteria

Almost never

1

Failure unlikely. History shows no failure.

Remote

2

Rare number of failures likely.

Very slight

3

Very few failures likely.

Slight

4

Few failures likely.

Low

5

Occasional number of failures likely.

Medium

6

Medium number of failures likely.

Moderately high

7

Moderately high number of failures likely.

High

8

High number of failures likely.

Very high

9

Very high number of failures likely.

Almost certain

10

Failure almost certain. History of failures exists from previous or similar designs.

QUALITATIVE SCALE FOR THE DELECTABILITY INDEX (D) Effect

Level

Criteria

Almost certain

1

Proven detection methods available in concept stage.

Very high

2

Proven computer analysis available in early design stage.

High

3

Simulation and/or modeling in early stage.

Moderately high

4

Tests on early prototype system elements.

Medium

5

Tests on preproduction system components.

Low

6

Tests on similar system components.

Slight

7

Tests on product with prototypes with system components installed.

Very slight

8

Proving durability tests on products with system components installed.

Remote

9

Only unproven or unreliable technique(s) available.

Almost impossible

10

No known techniques available.

IN THE TABLE THE HIGHEST RPN IS 108 FOR THE FAILURE MODE-ASSEMBLE AT ±12 DEGREES OFF-NOMINAL ANGLE, MOTOR WIRE IN WRONG LOCATION. THUS, IT DESERVES MAXIMUM ATTENTION FROM THE DESIGNERS IN ORDER TO AVOID FAILURES OF THE FAN ASSEMBLY DUE TO THIS PROBLEM.