TQM IEM Lecture Reliability FMEA TPM

Reliability, FMEA and TPM

© Tapan Bagchi TQM IEM Reliability

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Reliability • Generally defined as the ability of a product to perform as expected over time • Formally defined as the probability that a product, piece of equipment, or system performs its intended function for a stated period of time under specified operating conditions Tapan Bagchi TQM IEM Reliability

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Maintainability • The probability that a system or product can be retained in, or one that has failed can be restored to, operating condition in a specified amount of time.

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Types of Failures • Functional failure – failure that occurs at the start of product life due to manufacturing or material detects • Reliability failure – failure after some period of use

These relate to the ―bathtub curve‖. Tapan Bagchi TQM IEM Reliability

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Types of Reliability • Inherent reliability – predicted by product design • Achieved reliability – observed during use; based on observed failure data

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How do you measure Reliability? • Failure rate (l) – number of failures per unit time • Alternative measures – Mean time to failure – Mean time between failures (MTBF)

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Failure Rate Curve

“Infant mortality period”

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Cumulative Failure Rate Curve

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Average Failure Rate = 0.02

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Typical Forms of Failure  Early failure due to design faults, poor quality components, Failure Rate

manufacturing faults, installation errors,

operator & maintenance errors

 Useful life Early Failure

Useful Life

Time

Wear-out Failure

has a low, constant failure rate

 Wear-out failure parts approach the end of life

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Measuring Reliability  Reliability R(t): The probability of operating to an agreed level of performance  Unreliability F(t): The probability of failing to operate to an agreed level of performance

Rt   F t   1 Tapan Bagchi TQM IEM Reliability

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Reliability Function for Service Life • Probability density function of failure time is exponential: f(t) = le-lt for t > 0 • Probability of failure from (0, T) F(t) = 1 – e-lT • Failure rate = l • Reliability function R(T) = 1 – F(T) = e-lT Tapan Bagchi TQM IEM Reliability

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In general, Failure Times fit Weibull Distribution In probability theory and statistics, the Weibull distribution is a continuous probability distribution with the probability density function

for and f(x; k, λ) = 0 for x < 0, where k > 0 is the shape parameter and λ > 0 is the scale parameter of the distribution. The Weibull distribution is often used in the field of life data analysis due to its flexibility—it can mimic the behavior of other statistical distributions such as the normal and the exponential. If the failure rate decreases over time, then k < 1. If the failure rate is constant over time, then k = 1. If the failure rate increases over time, then k > 1. Tapan Bagchi TQM IEM Reliability

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The Weibull Distribution expressions

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Life Testing Data

Time t

Observed No. of Failure s n(t)

0

f(t)=

Cumulative No. of Failures

Surviving S(t)

0

2000

650 1

0.325 650

0.175 1000

3

0.105 1210

4

0.083

1376

5

0.066 1507

6

0.052 1610

7

0.041

1692

8

0.033 1757

9

0.060 1877

10

2000

0

0.500

0.395

0.605

0.312

0.688

0.247

0.754

0.195

0.805

0.154

0.846

0.122

0.879

0.062

0.939

0.656

123

Tapan Bagchi TQM IEM Reliability 0.062

123

0.500

0.236

243

120

0.325

0.235

308

65

0.675

0.233

390

82

0.000

0.235

493

103

1.000

0.235

624

131

F(t) = 1 - R(t)

0.235

790

166

R(t)= S(t)/20 00

0.298

1000

210

Reliability

0.388

1350

350 2

n(t)/ 2000

r(t) = n(t)/ avg S

16

2.000

0.000

1.000

r(t) and R(t) Calculations displayed Failure Rate vs. Time 2.500 2.000 1.500

r(t) Faiure Rate

1.000

Reliability R(t)

0.500 0.000 0

1

2

3

4

5

6

7

8

9

10

Time

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Reliability of Non-Repairable Items T1

T2 Td1

T3 Td2

Td3

 Mean Time To Fail (MTTF)

ratio of total up time to number of failures.

 Mean Failure Rate (l) inverse to MTTF.

 Mean Down Time (MDT) ratio of total down time to number of failures.

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Reliability of Repairable Items Tup1

Tup2 Td1

Tup3 Td2

Td3

T

 Total Up Time (Tup)

total time minus total down time

 Mean Time Between Failures

(MTBF)

ratio of total up time to number of failures.

 Mean Failure Rate (l) inverse to MTBF.

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Availability • Operational availability MTBF AO  MTBM  MDT • Inherent availability MTBF A MTBF  MTTR

MTBM = mean time between maintenance MDT = mean down time MTBF = mean time between failures MTTR = mean time to repair

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Design for Reliability  Element selection elements with well-established failure rate data

 Environment elements can withstand normal working environment

 Minimum complexity fewer elements (series systems)

 Redundancy several identical elements in parallel

 Diversity a give function is carried out by two parallel systems

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Series Systems

1

2

n

RS = R1 R2 ... Rn

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Reliability of Series System

O

I Rn

R2

R1

Reliability of a series system is the product of individual element reliabilities.

Rsystem  R1  R2    Rn e

 l1t

e

 ( l1  l2  ln ) t

e

 l2 t

 e

 ln t

System reliability is lower than the lowest element reliability

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Parallel Systems 1 2

n

RS = 1 - (1 - R1) (1 - R2)... (1 - Rn) Tapan Bagchi TQM IEM Reliability

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Reliability of Parallel System R1 I

R2

O

Reliability of a parallel system is determined by the product of individual element unreliabilities.

Rn Rsystem  1  F1  F2    Fn  1  (1  e l1t )  (1  e l2t )    (1  e lnt )

System reliability is greater than the greatest element reliability

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Series-Parallel Systems C

RA

RB

A

B

RC

RD D

C

RC

• Convert to equivalent series system RA

RB

A

B

RD C’

D

RC’ = 1 – (1-RC)(1-RC) Tapan Bagchi TQM IEM Reliability

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Reliability Management • Define customer performance requirements • Determine important economic factors and relationship with reliability requirements • Define the environment and conditions of product use • Select components, designs, and vendors that meet reliability and cost criteria • Determine reliability requirements for machines and equipment • Analyze field reliability for improvement Tapan Bagchi TQM IEM Reliability

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Configuration Management 1. Establish approved baseline configurations (designs) 2. Maintain control over all changes in the baseline programs (change control) 3. Provide traceability of baselines and changes (configuration accounting)

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Design Issues • Access of parts for repair • Modular construction and standardization • Diagnostic repair procedures and expert systems

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Maintainability • Maintainability is the totality of design factors that allows maintenance to be accomplished easily • Preventive maintenance reduces the risk of failure • Corrective maintenance is the response to failures Tapan Bagchi TQM IEM Reliability

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Reliability Engineering • • • • • •

Standardization Redundancy Physics of failure Reliability testing Burn-in Failure mode and effects analysis (FMEA) • Fault tree analysis (FTA) Tapan Bagchi TQM IEM Reliability

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FTA

Tapan Bagchi TQM IEM Reliability http://www.weibull.com/basics/fault-tree/index.htm

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Fault Tree Analysis (FTA) Bulb Fails

Example:

No electricity

Power Plant Fails

Wind Breaks Line

Power Line Fails

Glass Broken

Connector Corroded

Filament Broken

Impurities

Tree Breaks Line Tapan Bagchi TQM IEM Reliability

Vacuum Leak

Vibrations

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Bicycle fails when I rush to class Draw the FTA:

Hint: Draw an FTA diagram for the total system first.

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Faults/Pathways Magnified N-fold for a Simple Manufacturing Process!

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FMEA

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http://www.npd-solutions.com/fmea.html

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FMEA Failure Mode and Effect Analysis

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Failure, Likelihood, Impact… • Most real systems are designed to serve a purpose or deliver some function • But few systems are perfect—most are liable to failure. Then they fail to deliver their designed functionality • A car may not start, or its braking system may fail • The consequence of such failure may be drastic and its occurrence is generally uncertain • It is possible to plan contingent actions, or modify the design—to reduce (a) the likelihood of a failure, or (b) its impact, or (c) both • FMEA—an analytical procedure that helps one mitigate the risks by proactively reducing (a) the severity of the adverse situation, or (b) the likelihood (probability) of its occurrence 38

Steps for doing FMEA • Identify possible causes (modes) of failure • Estimate the likelihood of the cause being active • Determine the potential impact (severity) of the consequent failure • Calculate RPN—the Risk Priority Number—for this failure mode • Order the modes in descending order of RPN • Plan actions to reduce RPN, starting with the mode with the highest RPN—by reducing the likelihood (probability) of this failure mode becoming active, and/or by reducing its potential impact • Implement the preventive actions

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A Simple Example of performing FMEA • Mission: A family vacation at Goa • Modes that may cause the mission to fail: Sickness

Wallet lost

Strike

Vacation is spoiled

Accident

Travel mix up

Can’t find hotel 40

Severity × Likelihood = RPN Mode Sickness

Severity

Likeli-

(Impact)

hood

1

0.1

RPN 0.1

Possible Causes of failure Exposure Infection

Wallet lost

9

0.25

2.2

Unsafe One

acts

wallet

Strike

3

0.1

0.3

Did

not see news

Accident

8

0.2

1.6

Hazards Unsafe

Travel Mix up

5

Can’t find hotel

5

0.1

0.5

No

actions

reservation

Unreliable

0.25

0.63

No No

agent

reservation map; no car

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The ―Risk Map‖—before FMEA 10 Impact Wallet lost Accident

8

Strike

6

4

Travel mix up

No hotel

2

Sickness

0

0.2

0.4

0.6

0.8

42 1.0 Probability 

Mitigation actions facilitated by FMEA Causes

Severity

Likeli-

(Impact)

hood

Avoid

1

0.1

0.1

Safe keeping

3

0.1

0.3

Check news

1

0.1

0.1

Hazards

Identify and

2

0.1

0.2

Unsafe

Resolve Reserve seats through licensed agent

1

0.1

0.1

2

0.05

0.1

(things that may go wrong or fail) Exposure

Mitigation & proactive actions

RPN

Infection Unsafe One Did

No

acts

wallet

Split $; use Visa

not see news

actions

reservation

Unreliable

agent

No

reservation

Book ahead

No

map; no car

Carry map

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The Risk Map—After FMEA 10

Wallet lost

Impact

Accident

8

Strike

6 Travel

No Hotel

4

2 Sickness

0.0

0.2

0.4

0.6

0.8

44 1.0  Probability

Benefits of doing FMEA • It enhances system performance by helping one to identify adverse factors that may impact performance • It makes most of the risks visible, and helps one to quantify their impact and probability of occurrence • It helps one take proactive steps to prevent problems ahead of the system’s being put into service, e.g. in new product design and launch • It helps in reduction of waste and costs due to nonperformance caused by failures • Today FMEA is an indispensable tool in the hands of engineers, product and process designers, and trouble-shooters

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Increasing Probability of Occurrence

High-Level Combinations of Severity and Probability

High Risk

Medium Risk Low Risk

Increasing Severity of Harm/Consequence Tapan Bagchi TQM IEM Reliability

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FMEA – Why?

Introduction

• Why FMEA’s? • Definition, Purpose, Types, Benefits • Team Approach

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FMEA – Definition FMEA is a Structured group of activities which...

• Identify potential failure modes • Prioritize actions • Document the process.

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Failures

FMEA – Purpose

FMEA

Crisis

(Production start) Tapan Bagchi TQM IEM Reliability

Time 49

FMEA – Purpose FMEA’s are intended to ...

• Rate severity of failure modes • Identify actions to reduce occurence • Test adequacy of controls

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Potential failure Modes Failure Mode Type

Example

No function

Not operational

Partial function

Not all of function operating

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Severity (Weightfactor) What is the severity of each effect identified?

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Rating criteria for Severity (Weightfactor) Effect

Criteria: Severity of effect

Non-conforming with safety

Safety failure

Unacceptable risk

Correction is nescessary

Relative big risk

risico Minimum risk

None

Class

S A

Correction is recommended

B

Correctie isisnuttig Correction usefull

C C

AcceptedTapan failure Bagchi TQM IEM Reliability

D

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Potential Cause of Failure It is a weakness in the design with a failure mode as effect. (see next slide)

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Manufacturing misbuilds Due to design Deficiencies

+

+

-

-

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Manufacturing misbuilds Robust Design done after FMEA

+

+

-

-

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Searching for Causes of failure Use Fishbone Diagram: Text in wrong location “Text unreadable”

Ink of poor quality Tapan Bagchi TQM IEM Reliability

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Cause of failure – ―Why‖-ladder “Text unreadable” Ink doesn’t stick level 1

WHY?

Surface roughness not ok. level 2

WHY?

Design requirement level 3

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WHY?

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Sentencing Technique: Is it an effect or a cause? Could result in

Failure Mode

Effect

Due to

Cause

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Sentencing Technique Example Could result in

“Text Unreadable”

Due to

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Dissatisfied customer

Surface roughness (designreq.)

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Product-FMEA – Occurrence

What is the probability that the failure will occur?

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Rating criteria of occurrence Probability of failure Very high

Moderate

Low

Possible Failure Rates

Ranking

1 of 3

5

> 1 of 20

4

> 1 of 400

3

> 1 of 15000

2

< 1 of 15000

1

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Product-FMEA – Actions/Solutions

What are the possible actions to: - eliminate the failure - reduce effect - reduce occurrence

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Do the Bicycle exercise again—by FMEA

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Total Productivity Maintenance The Stars of TPM are the Japanese!

What is TPM?

What does maintenance mean anyway… Maintenance = The act of maintaining Maintain = To keep in a state of order. To keep in due (rightful, proper, fitting) condition, operation, or force; keep unimpaired.

Definition cont… Fix and Repair = Maintenance HOZEN (Maintenance in Japanese) = Maintaining and preserving perfection through Asset Management.

A common sight: Equipment breakdown, waiting for repair

The goal of TPM is to change “Buttonpusher Operators” to Process Owners or change Firefighters to Maintainers. It cuts downtime and losses and saves $.

The Five Pillars of TPM • • • • •

Autonomous Maintenance Maintenance Process Improvement Systematic Equipment Improvement Training and Skill Development Early Equipment Management

These are actualized through cross-functional Team-based improvement activities

TPM Goals T1

T2 Td1

T3 Td2

Td3

Characteristics of TPM

With TPM, Maintenance no more remains the job of only the ―Maintenance Staff!!!‖

Like Six Sigma, TPM is best executed by Cross-Functional Project Teams

Typical Cross-Functional TPM Team at work

Results delivered by TPM

TPM programs deliver Real $

Note carefully that these bring direct savings to the plant

But moving to TPM requires a Paradigm Shift

SEI—Systematic Equipment Improvement

Autonomous Maintenance

©2008 Productivity Inc. All Rights Reserved

What is Autonomous Maintenance?

Seven Steps of Autonomous Maintenance —Operators not only run the machines, they also maintain them 1. Conduct initial cleaning/inspection

5. Conduct general inspections

2. Eliminate sources of contamination

6. Improve workplace management and control

3. Establish provisional standards

7. Participate in advanced improvement activities

4. Develop general inspection training

Poor or neglected maintenance—no TPM thinking by users

What losses could it lead to?

Still not that rare in a factory!

Dr Bagchi saw a similar sight at a Jute Mill 6 months ago

TPM changes the scene: Cross-Functional Teams take over maintenance activities

Maintenance Process Improvement (MPI) (Planned, Scheduled Maintenance System)

The Different Maintenance Techniques

Maintenance Process Improvement (MPI) Activities

The Case of a TPM Culture at work

Old Chain guard

After TPM MPI action by operators

Six Major Losses due to Equipment maintenance being not up to mark

Motivation for doing TPM: How the 6 Losses reduce Effectiveness Overall Equipment Effectiveness

6 Major Losses

=

Availability

x

Perf. Efficiency

x

Quality

Equipment Failures

Reduced Speed

Rejects and Defects

Adjustments and Set-Ups

Minor Stops and Idling

Startup Losses

Systematic Equipment Improvement (Improve Equipment Effectiveness)

SEI A systematic approach to eliminate waste through analysis of the ―6‖ major losses utilizing cross-functional teams to continuously investigate, test, and implement improvements with a goal of maximizing equipment effectiveness. SEI is a DATA DRIVEN PROCESS. The goal is to reduce equipment failures, adjustments and setups, correct speed, and eliminate stops and idling— systematically. This engages reliability engineering and knowledge of the machines.

Training and Skill Development

Why does TPM require Training and Skills Development?

TPM Training needs are often obvious…

Just looking…taking a walk-around the workplace

A walk through the offices

―The part must be somewhere in here…‖

Well the drip seems fixed… must be busy time.

Clogged motor casing intake—that isn’t good. I know that, but the manager should get it cleaned!

I guess there is enough light …ya I pasted the sheet bit low ☺

―They should know what they are looking at…‖

Enter TPM

I like that!

And that too!

God! Don’t they have anything else to do other than shining dials all day? What did you say, ―TPM?!‖

Zero Breakdown Strategies Restore equipment Maintain basic equipment conditions

Adhere to standard operating procedures Improve operator maintenance skills

Don’t stop at emergency fixes Correct design weaknesses Study breakdowns relentlessly … if you care to survive in business.

TPM pushes down the floor and pushes out the wear-out end

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TPM Implementation—as the Japanese do it • • • • • • • • •

Announce top management’s decision to introduce TPM Launch educational campaign Create organizations to promote TPM Establish basic TPM policies and goals Formulate master plan for TPM development Hold TPM ―kickoff‖ Improve equipment effectiveness Establish an Autonomous maintenance program for operators Set up a scheduled maintenance program for the maintenance department • Conduct training to improve operator and maintenance skills • Develop initial equipment management program • Implement TPM fully and aim for higher goals