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Failure Mode and Effect Analysis

Lecture 2-2Fault Tree Analysis

ReliabilitySystem, Concept FMEA

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FMEAFault Tree Analysis

• Same basic approach as the Root Cause Analysis

• Allows a backward approach to systematically identify potential causes of failures

• Provides an overview of interrelationships between causes and effects

• Breaks down failures into more detail

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FMEAFault Tree Analysis

A logical, structured process that can help identify potential causes of system failure before the failures actually occur

Benefits• Identify possible system reliability or safety problems

at design time,• Assess system reliability or safety during operation• identify components that may need testing or more

rigorous quality assurance scrutiny,• Identify root causes of system failures

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FMEAWhen to Apply FTA

• Applied any time during the life of a plant, system, subsystem, or equipment item

• Primarily used to examine incidents or accidents whose consequences would be classified as catastrophic

• Often initiated after a major hazard has been recognized for the first time

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FMEAHow FTA is Used

• Fault trees are used to determine the frequency of top events for which historic data is not available or applicable

• Once the top event is defined, the fauslt tree is constructed by working downwards through the system, one level at a time, to determine what failures could occur which could lead to the top event

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FMEAFTA and FMEA Compared

Different basic purpose, or focus• FTA – focus on failure outcome

– Examines the applicable components, processes and conditions retroactively to identify all possible contributing factors that could have worked alone or in combination to cause the outcome

• FMEA – focus on each system component, and examines before-the-fact all things that could possible go wrong with that component.

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FMEAExample

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FMEAWhat is Reliability?

PERCEIVEDRISK

Competition Market PressureManagement Emphasis

Customer Requirements

Legal,Statutory

Safety

Warranty andService Costs

PublicLiability

DevelopmentRisks

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FMEADefinition of Reliability

The probability that a system or product will perform in a satisfactory manner for a given period of time when used under specified operating conditions.

elements of reliability, • satisfactory performance, • time, • specified operating conditions.

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FMEAReliability - Tasks

• Reliability program plan• monitor and control of

subcontractors & suppliers• Program reviews• Failure reporting, analysis, corrective

action system (FRACAS)• Reliability modeling, allocations,

predictionsource: MIL-STD-785B, 1980

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FMEAReliability - Tasks• Failure Mode Effect & Criticality

Analysis (FMECA)• Tolerance analysis• Effects of functional testing, handling,

packaging, transportation, and maintenance

• Environmental stress screening (ESS)• Reliability Qualification Test (RQT)• Production Reliability Acceptance Test

(PRAT)

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FMEAQuantification of Reliability

• Establishing reliability requirements or objectives

• Apportionment (budgeting)• Prediction• Analysis

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FMEADesign Testing

• Performance• Environmental• Stress• Reliability• Maintainability• Life• Pilot Run

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FMEAReliability Program Issues

• Define a reliability program• Develop goals and requirements• Design for Reliabilty• Assess reliability Progress• Measure product reliability• Ensure reliable performance

source: RAC Blueprint

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FMEAProduct Life

During the life of a product, failure occur in a predictable pattern known as a “bathtub curve.”

The curve can be divided into three regions:

Wearout(End of Life)

Early Life Failure

(Infant Mortality) Useful Life(Constant Failure Rate)

Time

Failu

res

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FMEAFMEA and Product Life

By eliminating failure modes, FMEAImproves the reliability of the product

Reduces the number of product failures experienced by the customer

Wearout(End of Life)

Early Life Failure

(Infant Mortality) Useful Life(Constant Failure Rate)

Time

Failu

res FMEA improves product

performancein all three areas

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FMEA

1. Develop a StrategyST91260A

DRIVE

BASE SUB

SYSTEM & FIRMWARE

COVERMEDIA

DISC PACK

FINAL ARM

ARM SUB

ARM COIL

BOBBIN

ROT. ARM

SP. FLEX SPINDLE

STATOR

ROTOR

HDA ASSEMBLY

BASE DECK

RECIR FILTER

BREATH. FILTER

LABELS

PCB ASSEMBLY

DISC CLAMP

BAL. WT

SPACERS

MAG ASSY LATCH

ARM SUB

ARM SUB

BASE DECK

DAMPER

SEAL

MOTOR POLES, POLE SPACER

Teams will be established to evaluate the application of FMEA in areas shown by the shading on the following diagram. Each "FMEA" Team under the direction of the FMEA Facilitator will:- ESTABLISH a strategy focusing on new technology, past issues, new or redesigned components, both from the product (design) and process perspectives..- PREPARE a Design and a Process FMEA for the selected components or subassemblies..- DETERMINE functions, potential failure modes, effects, causes, and verification activities planned or in-place.. - RECOMMEND corrective actions to the product team..

FIRST PRIORITY

SECOND PRIORITY

THIRD PRIORITY

Basic Steps

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FMEAPlanning

APPLICATIONNEW TECHNOLOGIESCOMPLEXITYRESOURCES

It would very costly to apply FMEA to every part. When planning for FMEA, consider:

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FMEA

1. Develop a Strategy

2. Review the design /process

EFFECTCAUSES

Basic Steps

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FMEAReview the Process

• Design– Drawings– Specifications– Bill of material

• Process– Flow process chart– Operator work instructions

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FMEA

1. Develop a Strategy2. Review the design /process

3. List functions

Basic Steps

• The task that the system, process, component subsystem or service must perform

• Very important in understanding the entire FMEA process

• Must be communicated in a concise and easily understood manner

• Use active verbs to describe the function

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FMEAFMEA is Function-drivenFMEA begins with a definition of the FUNCTIONS an

item or process step is supposed to perform. The inputs must come from several sources to be effective:

ManufacturingEngineer

SupplierQuality Reliability

EngineerDesign

Engineer

ProjectManager

Production

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FMEAFunctions/Features - Example

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FMEA1. Develop a Strategy2. Review the design /process3. List functions

4. Brainstorm potential failure modes

functionsfailure modes

Basic Steps

• The inability of the system, design, process or service to perform based on design intent.

• Failures that do not meet customer requirements

• Consider both known and potential failures

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FMEA

Failure to perform a defined functionSomething occurring that you don't expect, or wantWrong application

A Failure Mode is . . .

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FMEA

1. Develop a Strategy2. Review the design /process3. List functions4. Brainstorm potential failure modes

5. Organize potential failure modes topictopic

Affinity Diagram

Basic Steps

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FMEA

1. Develop a Strategy2. Review the design /process3. List functions4. Brainstorm potential failure modes5. Organize potential failure modes

6. Analyze potential failure modesPRODUCT: FMEA NO.

PROCESS/OPERATION: PAGE OF

DESIGN (OR PROCESS) FMEAPLANNING REFERENCE: DATE: BY:

Oklahoma CityPOTENTIAL POTENTIAL S POTENTIAL O CURRENT D RPN ACTION CORRECTIVE RESPONSIBILITY ACTION RESULTING

FUNCTION FAILURE MODE EFFECTS OF CAUSE(S) OF CONTROLS PRIORITY ACTION & DATE DUE TAKENFAILURE FAILURE S O D RPN

DETECTIONOCCURRENCESEVERITY RPN = S x O x D

Basic Steps

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FMEA

1. Develop a Strategy2. Review the design /process3. List functions4. Brainstorm potential failure modes5. Organize potential failure modes6. Analyze potential failure modes

7. Establish risk priorityVITALFEW

TRIVIALMANY

Basic Steps

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FMEA

1. Develop a Strategy2. Review the design /process3. List functions4. Brainstorm potential failure modes5. Organize potential failure modes6. Analyze potential failure modes7. Establish risk priority

8. Take action to reduce risk

Basic Steps

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FMEA

1. Develop a Strategy2. Review the design /process3. List functions4. Brainstorm potential failure modes5. Organize potential failure modes6. Analyze potential failure modes7. Establish risk priority8. Take action to reduce risk

9. Calculate resulting risk

Basic Steps

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FMEA

1. Develop a Strategy2. Review the design /process3. List functions4. Brainstorm potential failure modes5. Organize potential failure modes6. Analyze potential failure modes7. Establish risk priority8. Take action to reduce risk9. Calculate resulting RPN’s

10. Follow up

Basic Steps

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FMEASystem FMEA

1. Transform an operational need into a description of system performance parameters

2. Integrate related technical parameters and assure compatibility of:

– Physical– Functional Interfaces– ProgramTo optimize the total system design and

definition

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FMEASystem (Concept) FMEA

Goal: define and demonstrate a proper balance among operational and economic factorsMust be based on solid needs, wants and expectations of the customer (internal and external)

Outcome: preliminary design with baseline configuration, functional specifications