Industrial Maintenance

Chapter 4

Failures
Essential Root-Cause Analysis Tools
(FMEA, FTA, 5 Why, Fishbone ...)

Dr. Fatme Makssoud

 Course Objectives

Upon completion of this course, students should be able

to :

 Understand the failure mechanisms

 Understand the importance of performing root cause analysis
 Identify the root cause of a problem using the problem solving
process
 Understand the application of basic quality tools in the
problem solving process
Definition of Failure
Types of failures

There are several types of failure according to their :

 Cause:
- Intrinsic (improper design, manufacturing doesn’t meet the
design requirement, improper installation, wear, aging)
- Extrinsic (misuse, mishandling, improper maintenance)

 Degree: partial or complete, permanent

 Their rate of onset: sudden or gradual

Types of failures

Internal Failure: refers to any defects in a process that are

identified and eliminated before being delivered to the customer.

External Failure: An External Failure is any defective item,

unit, or output that passes through an entire process and is
received by the customer. External Failures lead directly to
customer dissatisfaction. External Failures are very costly.
Mechanisms of mechanical failure

 Failure by plastic deformation: under mechanical stress under

thermal stress
 Failure by ductile and brittle fracture and / or strain
 Failure of plastics and composites
 Failure by corrosion

Electrochemical Fe ⭢ Fe2+ +2e-

Chemical (chemical reaction 2H+ + 2e- ⭢ H2

Electrical (leakage, potential exchange )
For more information : https://www.youtube.com/watch?v=Aa2ieDEoPQ4

What is a Root Cause ?

ROOT CAUSE =

The causal or contributing factors that, if corrected, would prevent
recurrence of the identified problem


The “factor” that caused a a problem or defect and should be permanently
eliminated through process improvement


The factor that sets in motion the cause and effect chain that creates a
problem


The “true” reason that contributed to the creation of a problem, defect or
nonconformance
What is a Root Cause Analysis (RCA)?


A standard process of:
 identifying a problem
 containing and analyzing the problem
 defining the root cause
 defining and implementing the actions required
to eliminate the root cause
 validating that the corrective action prevented
recurrence of problem
 
Benefits
By eliminating the root cause…
You save time and money!

Problems are not repeated
 Reduce rework, scrap, retest, poor quality costs, etc…

Problems are prevented in other areas

Communication improves between groups and

Process cycle times improve (no rework loops)

Secure long term company performance and profits

$$ Less rework and Scrap = Increased profits!

Useful Tools for Determining Root Cause

 The “5 Whys” Model

 Fishbone Diagrams
 FTA : Fault Tree Analysis
 Failue Mode, Effect, Analysis (FMEA)
 Root-Cause-Analysis Tools: 5 Whys (Example I)

Problem
The 5 Why’s Analysis is a simple tool for
drilling down on the problem statement
until the root cause is identified asking 1. Why
“WHY” 5 times.
It is applicable when you are looking at one 2. Why
major cause and if it needs drill down to
arrive at one root cause 3. Why

 Avoid intentional or unintentional bias

4. Why
while answering
 Find the right person who can answer 5. Why
Root Cause
 Use other Tools complementary

screening for business health

 Root-Cause-Analysis Tools: 5 Whys (cont.)

The Process of the 5 Whys is often subdivided in 4 main steps:

2 3
1 4
Assemble Define the Ask
Implement
a problem « Why ?» corrective
Team actions

Defining the problem The team leader asks the Creation a list of
A team should be appropriate
clearly is the first thing team “Why” the problem
formed in order corrective actions.
in the 5 Whys technique occurred and the team
to conduct a that the team should answers the question.
brainstorming do. In this step, the He asks if the identified
session to detect problem should be causes were corrected,
the root cause of defined clearly. If the could the problem still
problem statement is occurs, If yes, he should
the problem. ask why again,,,,
clear and explanatory
enough, the team will
spend less time on
resolving it.

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Root Cause Analysis : « 5 Why » Example I
Problem statement – The client refused to pay the progress payment.

1. Why did the client refuse to pay the progress payment?

- Because we completed the activity late.

2. Why did we complete the activity late?

- Because the activity took longer than estimated.

3. Why did the activity take longer than estimated?

- Because we couldn’t procure enough material for the activity.

4. Why didn’t we bring enough material?

-Because we didn’t purchase on time.

5. Why didn’t we purchase the materials on time?

- Because we didn’t analyze the work schedule.

The root cause of the problem is that we didn’t analyze the work schedule. Corrective action is to
create good communication channels within the project team and assemble progress meetings
regularly to avoid a lack of communication and coordination.
Root Cause Analysis : « 5 Why » Example I (cont.)

Problem statement – The client refused to pay the progress payment.

Root Cause Analysis : « 5 Why » Example II
Identify Problem : A manager walks past the assembly line and notices a
puddle of water on the floor. Knowing that the water is a safety hazard, she
asks the supervisor to have someone get a mop and clean up the puddle.
The manager is proud of herself for “fixing” a potential safety problem.

Puddle of water on the floor

Why?

Leak in overhead pipe
Why?

Water pressure is set too high

Why?

Water pressure valve is faulty

Why?

Valve not in preventative maintenance program
 Root-Cause-Analysis Tools: Cause and Effect Diagram (Fishbone
Diagram)

The Fishbone Diagram is a tool used

for identifying the root cause based
on Cause & Effect relationship. They
are also called “Cause and Effect” or
“Ishikawa” Diagrams.
 Fishbone Diagrams are very useful
for the analysis of complex
problems
 Grouping the courses can be
based on the major cause analysis
shown previously
The Fishbone Diagram is applicable
when looking at numerous major
causes and you need drill down to
arrive a numerous root causes based
on their Cause and Effect
Relationships.

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Root-Cause-Analysis Tools: Fishbone Diagrams (cont.)

Fishbone diagrams help to identify the “6 Ms” (potential causes) that

may have contributed to the undesirable condition or problem.

 Draw fishbone diagram

• Place the effect at the head of the “fish”
• Include the 6 recommended categories (6M) shown below

Man Method Machine

Problem
or Issue

Material Environment Measurement System

The categories typically include:

- Man : Anyone involved with the process

- Methods : How the process is performed and the specific requirements for
doing it, such as policies, procedures, rules, regulations and laws

- Machines : Any equipment, computers, tools, etc. required to accomplish

the job

- Materials : Raw materials, parts, pens, paper, etc. used to produce the
final product

- Measurements : Data generated from the process that are used to

evaluate its quality

- Environment (Mother Nature) : The conditions, such as location, time,

temperature, and culture in which the process operates
 Example 1

The production and home delivery of a pizza is a relatively

straightforward and simple process.
Develop a fishbone diagram to identify potential defects and
opportunities for poor quality in this process.

Categories of possible quality problems might be related to

the ordering process, pizza construction, pizza ingredients,
packaging/boxing, time to receive order, order
accuracy/correctness, and pricing.
 Example 2
Develop a fishbone diagram for the possible causes of flight delays.
 Example 3
Develop a fishbone diagram for the possible causes of your car not starting.
 Example 3 (cont.)
Develop a fishbone diagram for the possible causes of your car not starting.
 Root-Cause-Analysis Tools: Fault Trees

A fault tree is a graphical

representation of the logical
structure displaying the
relationship between an
undesired potential event
(top event) and all its
probable causes.
➢Top-down approach to
failure analysis
➢Starting with a potential
undesirable event (top
event)
➢Determining all the ways
in which it can occur
➢Mitigation measures can
be developed to minimize
the probability of the screening for business health
undesired event
 Fault Trees (Steps)
The Fault Tree Analysis is executed in 5 major steps:

Fault tree analysis is

a logic diagram for
finding deductive
failures in which
using logic flows to
combine different
lower-level factors.
It is also used for
tracing all possible
important factors
and branches of
events.

screening for business health

Fault Trees (Example)

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 Fault Trees Analysis (FTA) : Gates And / Or

AND Gate G OR Gate G

Boolean Algebra

A+A=A
A.A = A
A.(A+B)=A
A+AB=A

screening for business health

 Series diagram (OR)
Undesirable Event (UE)

OR gate represents SERIES

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 Parallel (Redundancy) diagram (AND)

Undesirable Event (UE)

OR gate represents PARALLEL

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Fault Trees Analysis (FTA) : Example II

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 Fault Trees Analysis (FTA) : Probability

For AND and OR gates the probabilities are easily calculated:

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Fault Trees Analysis (FTA) : Example I

Probability
of failure
on demand

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 Fault Trees Analysis (FTA) : Example I
Problem statement – Find the probability of water pump failure from the below example.

The water pump will fail because of (valve failure and valve closed) or (fault indicator or light fail or control command
fails or operator unable to open the valve). Since OR gates add and AND gates multiply the probability of pump failure.

Ppumpfail = (0,05*0,05) + {1 – [(1 – 0,003)*(1 – 0,002)*(1 – 0,018)*(1 – 0,02)]}

Ppumpfail = 0,0025 + {1- [0,997 * 0,998 * 0,982 * 0,98]} = 0,0025 + (1 – 0,95755) = 0,0025 + 0,04244 = 0,04494

Hence, the probability of water pump failure = 4,49 % screening for business health
Fault Trees Analysis (FTA) : Example III

A + AB = A screening for business health

d1d3d4 + d1d3d5 + d1d3
Failure Mode, Effect, Analysis (FMEA)

Failure Modes & Effects Analysis (FMEA) is a risk

management tool that identifies and quantifies the influence of
potential failures in a system.

FMEA analyzes potential failures using three criteria:

1. Occurrence (failure cause and frequency)
2. Severity (determine failure mode and its effect)
3. Detection (likelihood of failure detection)

screening for business health

See File : FMEA_Fatme.pdf
 Scrap Estimate

• Geometric or quality defects material wasted

(scrap)
• Market estimate + scrap estimate
= number of units scheduled for production

• Scrap estimates:
• Pk : percentage of scrap produced in k-th operation
• Ok : desired non-defective output from k-th operation
• Ik : input requirement to k-th operation

41
Phase I: Scrap Estimate ...

= Ik+1

On
I1 
(1  P1 )(1  P2 )......(1  Pn )

42
 Exercise 1 (Serial)
• A product has a market estimate of 97,000 components
and requires three processing steps (turning, milling
and drilling), having defective estimates of 0.04, 0.01
and 0.03. the market estimate is the output required
from step 3.
• what is the amount of raw material required for
operation 1?

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Exercise 2 (No-serial)
 Exercise 3

I3 = (1 – d1) I1 + (1 – d2) I2
I3 = (1 – d1) I1 + (1 – d2) d1 I1
I3 = I1 ((1 – d1) + (1 – d2) d1 )
=> I1 = I3 / (1 – d1) + (1 – d2) d1
I3 = O3 / (1 – d3) alors
I1 = O3 / (1 – d3) ((1 – d1) + (1 – d2) d1 ) 45
 Exercise 3 (cont.)

• End product requirement is 100,000 pieces. Based

on the given rework assumption earlier, calculate
the number of units required for processing at the
first operation. Defective rates are 0.03, 0.40 and
0.02 respectively.

• I1=100,000/0.98(0.97+0.03(0.60))=103,280

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Exercise 4 : Calculating production requirements for assembled products
We assume that the components are outsourced and the final assembly is performed locally.
The final products are two assemblies requiring three components. Assembly1 requires 4
units of component 1 and 3 units of component 2, Assembly 2 requires 2 units of component
2 and 1 unit of component 3. The percentage defectives are d 1 = 0.06, d2 = 0.05, d3 = 0.04, d4 =
0.03 et d5 = 0.02.

47
 Exercise 5
• A company manufactures 3 products (P1, P2 and
P3) from 4 raw material. These products are
produced in 6 machines that have scrap rates. The
demand of P1, P2 and P3 is 2000, 1000 and 3000
units respectively. The production process is given
below.
The purchasing department wants to know the number of
raw materials needed.
Calculate input and output values for each machine and raw
material needed.

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 ZONE D’INVENTAIRE

I1 I2 I3 I4
2053 2062/(1-0.05)= 2171 3222 3357
p1I1
M1 M4 M6
2053*0.3= 616 3222
p1:0.3 p4:0.05 p6:0.04

(1-p1)I1
1031*2= 2062
2053*0.7
M3 p3:0.02
= 1437 1031*3= 3093
(2)
(1-p3)p1I1 = 604
A (3)
(1-p3)p1I1+(1-p1)I1=2000/(1-p2) 3000/(1-0.02)
= 3061 1000/(1-0.03)= 1031
(1-0.02)0.3I1+(1-0.3)I1=2000/(1-0.02)
(0.98*0.3I1+0.7I1=2041
0.994I1=2041 M2 M5
I1=2053 p2:0.02 p5:0.03
P3 P1 P2
(3000) (2000) (1000) ZONE DE STOCK