BasicTools-CauseandEffectDiagram

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Cause andEffect Diagram

Sector Enterprise Quality Quality and Mission AssuranceNorthrop Grumman CorporationIntegrated Systems

CA/PA-RCA : Basic Tool


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What is Cause and Effect Analysis

Cause and Effect Analysis is a technique for

identifying all the possible causes (inputs)

associated with a particular problem / effect

(output) before narrowing down to the small

number of main, root causes which need to

be addressed.


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Cause and Effect Analysis is a valuable tool for:

Focusing on causes not symptoms capturing the

collective knowledge and experience of a group

Providing a picture of why an effect is happening Establishing a sound basis for further data

gathering and action

Cause and Effect Analysis can also be used to

identify all of the areas that need to be tackled to

generate a positive effect.

Why use Cause and Effect Analysis


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What is a Cause and Effect Diagram

A Cause and Effect diagram (also known as a Fishbone or

Ishikawa diagram) graphically illustrates the results of the

analysis and is constructed in steps. Cause and Effect

Analysis is usually carried out by a group who all have

experience and knowledge of the cause to be analyzed.

Cause-and-Effect diagrams graphically display potential

causes of a problem

The layout shows Cause-and-Effect relationships between

the potential causes


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Why use a Cause and Effect Diagram

It is common for people working on improvement efforts to jump

to conclusions without studying the causes, target one possible

cause while ignoring others, and take actions aimed at surface

symptoms

Cause-and-effect diagrams are designed to:

Stimulating thinking during a brainstorm of potential causes

Providing a structure to understand the relationships between

many possible causes of a problem

Giving people a framework for planning what data to collect

Serving as a visual display of causes that have been studied

Helping team members communicate within the team and with

the rest of the organization


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How do I do it?

1. Identify the Problem/Issue

Select a particular problem, issue or effect.

Make sure the problem is specific, tightly defined

and relatively small in scope and that everyone

participating understands exactly what is being

analyzed.

Write the problem definition at the top of the flip

chart or whiteboard.


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How do I do it? (continued)

2. Brainstorm

Conduct a Brainstorm of all the possible causes of the effect, i.e., problem.

Have a mixed team from different parts of the process (e.g.,

assemblers and testers).

Get a fresh pair of eyes - from someone who is not too close to the

process.

Have a facilitator - an impartial referee.

Everyone is an equal contributor (leave stripes at the

door).

Fast and furious - go for quantity rather than quality (of ideas) at first.

Involve everyone, or question why he/she is here.

Timing - set an upper limit and best time/day of the week.

Offer an incentive (free lunch?). Know when to stop.

Recognize that this is a snapshot of how the group thinks today.

Re-visit the problem again.

Refer also to the Process Mapping tool.

Consider (how) should you involve your customer?


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2. Brainstorm (continued)

Write each idea on a Post-It to make it easy to transfer them

onto the fishbone diagram later. Be careful not to muddle

causes and solutions at this stage.

It is important to brainstorm before identifying cause

categories otherwise you can constrain the range of ideas.

However, if ideas are slow in coming use questions such as,

what about?, to prompt thoughts.


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3. Draw fishbone diagram Place the effect at the head of the fish Include the 6 recommended categories shown below

Problem

or Issue

Method Machine

Environment Measurement System

People

Material


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4. Align Outputs with Cause Categories

Review your brainstorm outputs and align with the

recommended major cause categories, e.g., the People,

Method, Machine, Material, Environment and Measurement

System.Note:

These may not fit every situation and different major categories

might well be appropriate in some instances, however, the total

should not exceed six. Other categories may includeCommunications, Policies, Customer/Supplier Issues etc.

Tip !

The 6 categories recommended will address almost all scenarios. However, there is no

one perfect set of categories. You may need to adapt to suit the issue being analyzed.


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5. Allocate Causes Transfer the potential causes from the brainstorm to the

diagram, placing each cause under the appropriate category.

If causes seem to fit more than one category then it is

acceptable to duplicate them. However, if this happens

repeatedly it may be a clue that the categories are wrong and

you should go back to step 4.

Related causes are plotted as twigs on the branches. Branches

and twigs can be further developed by asking questions such as

what?, why? how?, where? This avoids using broadstatements that may in themselves be effects. Beware, however,

of digging in and getting into bigger issues that are completely

beyond the influence of the team.


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6. Analyze for Root Causes Consider which are the most likely root causes of the effect. This

can be done in several ways:

Through open discussion among participants, sharing views

and experiences. This can be speeded up by using Consensus

Decision Making.

By looking for repeated causes or number of causes related to a

particular category.

By data gathering using Check Sheets, Process Maps, or

customer surveys to test relative strengths through Pareto

Analysis.

Once a relatively small number of main causes have been

agreed upon, Paired Comparisons, can be used to narrow down

further.

Some groups find it helpful to consider only those causes

they can influence.


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7. Test for Reality

Test the most likely causes by, e.g., data gathering and observation if

this has not already been done.

The diagram can be posted on a wall and added to / modified as

further ideas are generated either by the team or by others who can

review the teams' work.

Cause and Effect Analysis can be combined with Process Mapping.

A fishbone may be developed for each discrete activity within the

process that is generating the output / effect so that causes are

linked to particular steps in the process.


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Sources of Variation - People

Types of Questions that may be AskedNote, this is not a definitive list of questions that may be asked to identify potential source of variation

Does the person have adequate supervision and support?

Does the person know what he is expected to do in his job?

How much experience does the person have?

Does the person have the proper motivation to do his best work?

Is the person satisfied or dissatisfied with his job?

Is the person more- or less-productive at certain times of the day? Do physical conditions such as light or temperature affect their work?

Does the person have the tools/equipment needed to do the job?

Who does the person contact when problems arise?

Is the work load reasonable?

The activities of the workers. Variations caused by skill, knowledge, competency and

attitude


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Sources of Variation - Method

The methods used to produce the products. Variations caused by inappropriate methods or processes.


How is the method used defined?

Is the method regularly reviewed for adequacy?

Is the method used affected by external factors?

Have other methods been considered?

How does the operator know if the method is operating effectively?

Is statistical analysis used to verify the effectiveness of the method?

What adjustments must the operator make during the process?

Have any changes been made recently in the process?


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Sources of Variation - Machine

The equipment used to produce the products. Variations caused by temperature, tool wear and vibration.


How old is the equipment or machinery?

Is it maintained regularly?

Is the machine affected by heat or vibration or other physical factors?

How does the operator know if the machine is operating correctly?

Is statistical analysis used to verify the capability of the machine? What adjustments must the operator make during the process?

Have any changes been made recently in the process?


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Sources of Variation- Material The "ingredients" of a process.

Variations caused by materials that differ by industry, product

and stage of production.


How is the material produced?

How is the material verified?

How old is the material?

How is quality judged prior to your operation?

What is the level of quality?

How is the material packaged?

Can temperature, light or humidity affect the material quality?

Who is the material supplier?

Has there been a change in suppliers?


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Sources of Variation - Environment

The methods used to control the environment. Variations caused by temperature changes, humidity etc.


How are environmental conditions monitored?

How are environmental conditions controlled?

How is the environment control measuring equipment calibrated?

Are there changes in conditions at different times of the day?

How does environmental change impact the processes being used? How does environmental change impact the materials being used?


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Sources of Variation Measurement System

The methods and instruments used to evaluate products.

Variations caused by measuring techniques, or calibration and

maintenance of the instruments.

Types of Questions that may be Asked

Note, this is not a definitive list of questions that may be asked to identify potential source of variation

How frequently are products inspected?

How is the measuring equipment calibrated?

Are all products measured using the same tools or equipment?

How are inspection results recorded?

Do inspectors follow the same procedures? (Is there a set of

standards?)

Do inspectors know how to use the test equipment?


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Example (showing 4 of the 6 recommended categories)

PARTDIMENSIONAL

QUALITY

MACHINEMETHOD

MANPOWER MATERIAL

PROCESSKNOWLEDGE

TRAINING

SHIFT

OVERTIME

INSPECTION AVAILABILITY

THERMAL EXPANSION

PART DEFORMATION

MACHINABILITY

STRENGTH

REPEATABILITY

POSITIONING ACCURACY

BACKLASH

RIGIDITY

NC PROGRAM

FEED FORCE SPEED

TEMP

CUTDEPTHTOOL PATH

INSERT

TYPEGRADE

HOLDINGFIXTURE

GAUGE

REPEATABILITY

REPRODUCABILITY

COOLANT


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Cause and Effect Diagram

Questions?Call or e-mail:

Bob Ollerton

310-332-1972/310-350-9121

[email protected]

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