12 cause n effect n fta

7/28/2019 12 Cause N Effect N FTA

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Lean Six Sigma Operational - Delegate Workbook

SSG06101ENUK - FTaCEA/Issue 1.1/May 2008 1 The British Standards Institution 2008

Cause and Effect Diagramsand Fault Tree Analysis

2

SSG06101ENUK Delegate Slides/Issue 1.1/ Mar 2008

Learning Objectives

At the end of this section delegates will be able to:

Understand the role of Cause/Effect and Fault Tree Analysis

within the DMAIC Improvement Process

Understand how to use a Cause/Effect diagram to structure the

output of brainstorming activities

Construct a Fault Tree from Top Event down to actionable Basic

Events

Identify appropriate actions to close a branch of the tree

Recognise that Fault Tree can be used both as a prevention tool

and a diagnostic tool


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3


Agenda

Cause/Effect Diagrams

Fault Tree Analysis Within DMAIC

Fault Tree Analysis Roadmap:

Define Top Event

Define scope of system

Understand system

Construct Fault Tree

Analyse the Tree

Closing Actions

Summary

Workshop

4


The Diagrams

Cause & Effect Diagrams and Fault Trees are

both pictorial methods for logically deriving the

causes that may explain the occurrence of an

event


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Cause & Effect Diagrams

6


Cause and Effect Diagram

Purpose

Identify potential causes of problems

Summarise process knowledge

Identify sources of variation

Facilitate brainstorming


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7



Benefits

Increase awareness of factors involved

Encourage staff participation

Focus on root causes

Determine preventive / corrective actions

8


PEOPLE MACHINES ENVIRONMENT

Poorbond

Training

Shift change overTemperature

Time

Pressure

Drop sizeDust

Lighting

Clean

Heat

Humidity

Batch variation

Viscosity

Age of Adhesive

Temperature

Cleaning method

Orientation

METHODS MATERIAL MEASUREMENT

Gauge



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9


CAUSES


High

Absenteeism

People Method

Environment Machine

Low morale

Internal

Competition

Low trust

Poor

training

Too little

responsibility

Poor reward system

Little

feedback

Poor budgeting

Too little

equipment

Poor

maintenance

Difficult to

operate

Wrong person in

the job

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Incorrect

shipments

Environment

Measurements

Methods

Material

Machines

Personnel

Keying data errors

Customer error

Mistakes

Don't Care

Lack of training

Part-time staff

Stock Code Errors ondatabase

Parts

Incorrect

shipments

Environment

Measurements

Methods

Material

Machines

Personnel

Keying data errors

Customer error

Mistakes

Don't Care

Lack of training

Part-time staff

Stock Code Errors ondatabase

Parts in wronglocations

Unclear Stock List

Keying data errors

Weighing check

Weighing doesn'twork

Too much walking

Dirty location labels

Poor stores lighting

Fishbone Diagram


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Incoming

StagingGauging

Work

Station 2Welding Trimming Gauging Grinding

SpeedFeed

Pressure

Speed

Feed

Pressure Temp

Feed

Speed

Pressure

TrimSteelCond.

Thickness

Impurities

Shape MaterialMovement

Shape

Gap

TipCondition

Current

TrimPlacement

Work

Station 1


12



Ishikawa suggests the following additional steps:

Step 1: When the relationship between a cause and the

effect can be shown quantitatively, draw a box around the

cause.

Step 2: When the relationship between a cause and the

effect is known to exist, but is diff icult to quantify, underline

the cause.

Step 3: When there is no real proof of the relationship

between a cause and the effect, do not mark the cause in

any way.


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Risks & Limitations

Focus on uncontrollable issues

Laying blame

Ideas are not fully explored

Only standard categories used

Fault Tree Analysis (FTA)


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DMAIC Improvement ProcessDefine ImproveMeasure Control

Control Criticalxs

Monitor ys

Validate ControlPlan

Close Project

1 5 10 15 20

10.2

10.0

9.8

9.6

Upper Control Limit

Lower Control Limit

y

Phase Review

Analyse Characterise xs

Optimise xs

Set Tolerances for xs

Verify Improvement

15 20 25 30 35

LSL USL

Phase Review

y=f(x1,x2,..)

y

x

. . .. . .

. .. . .

. .

.

Identify Potentialxs

Analyse xs

Select Critical xs

Phase Review

Run 1 2 3 4 5 6 7

1 1 1 1 1 1 1 12 1 1 1 2 2 2 23 1 2 2 1 1 2 24 1 2 2 2 2 1 15 2 1 2 1 2 1 26 2 1 2 2 1 2 17 2 2 1 1 2 2 18 2 2 1 2 1 1 2

Effect

C1 C2

C4

C3

C6C5

x

xx x

x

xx

xx x

x

Select Project

Define ProjectObjective

Form the Team

Map the Process

Identify CustomerRequirements

Identify Priorities

Update Project File

Phase Review

Define Measures (ys)

EvaluateMeasurement System

Determine ProcessStability

Determine ProcessCapability

Set Targets forMeasures

15 20 25 30 35

LSL USL

Phase Review

Define ImproveMeasure Control Control Critical

xs

Monitor ys


Close Project

1 5 10 15 20

10.2

10.0

9.8

9.6

Upper Control Limit

Lower Control Limit

y

Phase Review

Control Criticalxs

Monitor ys


Close Project

1 5 10 15 20

10.2

10.0

9.8

9.6

Upper Control Limit

Lower Control Limit

yy

Phase Review


Optimise xs


Verify Improvement

15 20 25 30 35

LSL USL

Phase Review

y=f(x1,x2,..)

y

x

. . .. . .

. .. . .

. .

.

15 20 25 30 35

LSL USL

15 20 25 30 35

LSL USL

Phase Review

y=f(x1,x2,..)

y

x

. . .. . .

. .. . .

. .

.

y=f(x1,x2,..)

y

x

. . .. . .

. .. . .

. .

.


Analyse xs

Select Critical xs

Phase Review

Run 1 2 3 4 5 6 7

1 1 1 1 1 1 1 12 1 1 1 2 2 2 23 1 2 2 1 1 2 24 1 2 2 2 2 1 15 2 1 2 1 2 1 26 2 1 2 2 1 2 17 2 2 1 1 2 2 18 2 2 1 2 1 1 2

Effect

C1 C2

C4

C3

C6C5

x

xx x

x

xx

xx x

x

Phase Review

Run 1 2 3 4 5 6 7

1 1 1 1 1 1 1 12 1 1 1 2 2 2 23 1 2 2 1 1 2 24 1 2 2 2 2 1 15 2 1 2 1 2 1 26 2 1 2 2 1 2 17 2 2 1 1 2 2 18 2 2 1 2 1 1 2

Run 1 2 3 4 5 6 7

1 1 1 1 1 1 1 12 1 1 1 2 2 2 23 1 2 2 1 1 2 24 1 2 2 2 2 1 15 2 1 2 1 2 1 26 2 1 2 2 1 2 17 2 2 1 1 2 2 18 2 2 1 2 1 1 2

Effect

C1 C2

C4

C3

C6C5

x

xx x

x

xx

xx x

x

Select Project


Form the Team

Map the Process


Identify Priorities

Update Project File

Phase Review

Select Project


Form the Team

Map the Process


Identify Priorities

Update Project File

Phase Review






15 20 25 30 35

LSL USL

Phase Review

15 20 25 30 35

LSL USL

15 20 25 30 35

LSL USL

15 20 25 30 35

LSL USL

Phase Review

16


Introduction to Fault TreeAnalysis Fault Tree Analysis (FTA) is a graphical tool for analysing

possible causes of a failure.

Can be used as a Prevention Tool - prevent the failuremode from occurring.

Or can be used as a Diagnostic Tool - identify what causedthe failure

Focuses on a single failure mode (as opposed to FMEA thatlooks at all failures)

In Six Sigma it can be used to help identify the CriticalInputs or Process Steps (xs) (Analyse), and developimprovements and controls for the Critical Inputs or ProcessSteps (xs) (Improve/Control)


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Fault Tree Analysis Roadmap

Step 2:

Define Scope of System

Step 3:

Understand System.

Step 1:

Define Top Event.

Step 4:


Step 5:

Analyse the Tree

Step 6:

Closing Action.

Step 2:


Step 3:

Understand System

Step 1:

Define Top Event

Step 4:


Step 5:

Analyse the Tree

Step 6:

Closing Action

18


Step 1 Define Top Event

The Top Event is the major failure to be analysed in the

fault tree

Within Six Sigma DMAIC this typically will be the issue(s)

identified in the measure phase eg delay in invoice

payment, incomplete order shipment etc

When identifying, consider main functions of processes,

major customer effects, historical failures

A separate fault tree should be generated for each top

event that is a fundamental concern


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Step 2 Define Scope of System

What comprises the system (transactional process) to be

analysed:

Which parts/process steps will be considered?

Which parts/process steps will be outside the scope

(responsibility of supplier or third party)?

What level of detail ? (macro/micro process steps)

System can consist of manual steps and / or automated

steps (eg IT system)

20


Step 3 Understand the System

The relevant experts (IT, Process Operators etc)

explain the function of each part/process step to

the team

Supported by: Process Maps

Specification Documents

Walking the process

Customer Feedback data


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DarkRoom

Bulb blown

Switch failedto close

No powerFuse blown

Power cut

AND OR

AND Gate OR Gate

OR OR

AND Battery failureLoss ofpower

Step 4 Construct Fault Tree

22



Top Event Intermediate Events

BasicEvent

ClosingAction

Specification

SupplierQuality

Process

OROR OROR OROR

ANDAND


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Step 4 Construct Fault TreeTop Event Main failure to be investigated

Basic Events Events leading to (causing)top event. Sequenced fromhigh level to lower level(Macro process step tomicro step).

Intermediate Events Lowest level events within

scope of FTA. Actionablelevel of detail. Three types ofbasic events should beconsidered (although not allmay be present).

24


Basic Event Types

Event relates to inadequate or incorrectprocessing, eg information entered

incorrectly.

SpecificationRelated

Supplier QualityRelated

Process Related

Event relates to incorrect specificationeg information not specified asrequired

Event relates to supplier not meetingspecification, eg incorrect information

provided.



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Method 1

Brainstorm all possible events (causes) that might lead to TopEvent

Transfer to Post-Its or cards

Sort into groups of events for related parts

Organise into a tree structure with Top Event on left side,branching to the Basic Events on the right

Method 2

Starting from the top event and ask the question how could thishappen ?

Work on each branch in turn, repeating the question how couldthis happen?

In practice a combination of both methods can be used

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Step 5 Analyse Tree

Check:

All known (historical) failures shown

Sequence of events from left to right

All branches have been developed to an

actionable level

Optional step :

Prioritise the basic events in terms of their probability of

occurrence.


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Step 6 Closing Action

ALL Basic Events should have a closing action

Level / depth of action dependent upon the level of concern

(occurrence)

Three areas of focus:

Specification Validation to ensure that the transactional

process has been correctly specified

Supplier Quality- to ensure that any process inputs are correct

Process Control to ensure that the transactional process is

operated correctly

Action not closed (signed off) until completed

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Step 6 Closing Action

Typical closing actions include:

Standard Operating Procedures, SOPs

Operator Training

Mistake Proofing

Statistical Process Control, SPC

Control Plan


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Fault Tree Analysis Roadmap

Step 2:


Step 3:

Understand System.

Step 1:

Define Top Event.

Step 4:


Step 5:

Analyse the Tree

Step 6:

Closing Action.

Step 2:


Step 3:

Understand System

Step 1:

Define Top Event

Step 4:


Step 5:

Analyse the Tree

Step 6:

Closing Action

32


DMAIC Improvement ProcessDefine ImproveMeasure Control

Control Criticalxs

Monitor ys


Close Project

1 5 10 15 20

10.2

10.0

9.8

9.6

Upper Control Limit

Lower Control Limit

y

Phase Review


Optimise xs


Verify Improvement

15 20 25 30 35

LSL USL

Phase Review

y=f(x1,x2,..)

y

x

. . .. . .

. .. . .

. .

.


Analyse xs

Select Critical xs

Phase Review

Run 1 2 3 4 5 6 7

1 1 1 1 1 1 1 12 1 1 1 2 2 2 23 1 2 2 1 1 2 24 1 2 2 2 2 1 15 2 1 2 1 2 1 26 2 1 2 2 1 2 17 2 2 1 1 2 2 18 2 2 1 2 1 1 2

Effect

C1 C2

C4

C3

C6C5

x

xx

xx

xx

xx

x

x

Select Project


Form the Team

Map the Process


Identify Priorities

Update Project File

Phase Review






15 20 25 30 35

LSL USL

Phase Review

Define ImproveMeasure Control Control Critical

xs

Monitor ys


Close Project

1 5 10 15 20

10.2

10.0

9.8

9.6

Upper Control Limit

Lower Control Limit

y

Phase Review

Control Criticalxs

Monitor ys


Close Project

1 5 10 15 20

10.2

10.0

9.8

9.6

Upper Control Limit

Lower Control Limit

yy

Phase Review


Optimise xs


Verify Improvement

15 20 25 30 35

LSL USL

Phase Review

y=f(x1,x2,..)

y

x

. . .. . .

. .. . .

. .

.

15 20 25 30 35

LSL USL

15 20 25 30 35

LSL USL

Phase Review

y=f(x1,x2,..)

y

x

. . .. . .

. .. . .

. .

.

y=f(x1,x2,..)

y

x

. . .. . .

. .. . .

. .

.


Analyse xs

Select Critical xs

Phase Review

Run 1 2 3 4 5 6 7

1 1 1 1 1 1 1 12 1 1 1 2 2 2 23 1 2 2 1 1 2 24 1 2 2 2 2 1 15 2 1 2 1 2 1 26 2 1 2 2 1 2 17 2 2 1 1 2 2 18 2 2 1 2 1 1 2

Effect

C1 C2

C4

C3

C6C5

x

xx

xx

xx

xx

x

x

Phase Review

Run 1 2 3 4 5 6 7

1 1 1 1 1 1 1 12 1 1 1 2 2 2 23 1 2 2 1 1 2 24 1 2 2 2 2 1 15 2 1 2 1 2 1 26 2 1 2 2 1 2 17 2 2 1 1 2 2 18 2 2 1 2 1 1 2

Run 1 2 3 4 5 6 7

1 1 1 1 1 1 1 12 1 1 1 2 2 2 23 1 2 2 1 1 2 24 1 2 2 2 2 1 15 2 1 2 1 2 1 26 2 1 2 2 1 2 17 2 2 1 1 2 2 18 2 2 1 2 1 1 2

Effect

C1 C2

C4

C3

C6C5

x

xx

xx

xx

xx

x

x

Select Project


Form the Team

Map the Process


Identify Priorities

Update Project File

Phase Review

Select Project


Form the Team

Map the Process


Identify Priorities

Update Project File

Phase Review






15 20 25 30 35

LSL USL

Phase Review

15 20 25 30 35

LSL USL

15 20 25 30 35

LSL USL

15 20 25 30 35

LSL USL

Phase Review


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Summary

Analyse - Fault Tree can be used to identify possible Critical

Inputs or Process Steps (xs) that are causing the poor

performance in Process Outputs (ys)

Improve - Fault Tree can be used to help identify how the

Critical Inputs or Process Steps (xs) might be changed /

eliminated / controlled to improve the Process Output (y)

Control - Fault Tree can be used to identify appropriate

controls for the Critical Inputs or Process Steps (xs)

Control - Fault Tree can be used as a diagnostic tool to

identify corrective action when a failure occurs

34


Workshop Construct A Fault TreeAnalysis Develop a Fault Tree Analysis for the given Top Event and

Transactional Process scope

Understand the System (for a transactional process application,develop/review the process flow)

Brainstorm How could top event happen?. Put each idea onto a

post-it as it is generated Organise the post-its into the tree structure, starting with the top

event on the left, working towards the root causes (basic events)on the right

Analyse the tree to check that the branches are logical and identifyany missing causes

Identify closing actions for the five most likely causes (use theFMEA Occurrence rating if required)

Prepare a short presentation on your team's findings