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“TQM / 7 QC Tools”

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Introduction• The 7 QC Tools are simple statistical tools used for problem

solving• Inspired after seven famous weapons of Benkei. Viz 1. Masakari-Broad Axe2. Kumade- Rake3. Nagihama - Sickle weapon4. hizuchi- Wooden mallet5. Nokogiri- Saw6. Tetsubo- iron staff7. sasumata- Half moon spear• It was possibly introduced by Kaoru Ishikawa who in turn was

influenced by a series of lectures W. Edwards Deming had given to Japanese engineers and scientists in 1950

Conti…

• “The term “7 tools for QC” is named after the 7 tools of the famous warrior,Benkei. Benkei owned 7 weapons, which he used to win all his battles. Similarly, from my own experience, you will find that you will be able to solve 95% of the problems around you if you wisely use the 7 tools of QC.”

- ISHIKAWA KAORU, Professor Emeritus, University of Tokyo• These tools have been the foundation of Japan's astonishing

industrial resurgence after the second world war.

Basic QC Tools

• The following are the 7 QC Tools :1.Pareto Diagram2.Cause & Effect Diagram3.Histogram4.Control Charts5.Scatter Diagrams6.Flowchart7.Check Sheets

Pareto Diagram 1/2• Origin of the tool lies in the observation by an Italian economist

Vilfredo Pareto that a large portion of wealth was in the hands of a few people.

• Dr.Juran suggested the use of this principle to quality control for separating the "vital few" problems from the "useful many".

• Also referred as 80/20 rule viz your 80% of problems are due to 20% of cause.

• It is used in the field of materials management for ABC analysis. 20% of the items purchased by a company account for 80% of the value. These constitute the A items on which maximum attention is paid

• It works on cumulative frequency and shows how few items exert maximum influence

Pareto Diagram 2/2For E.g• 80 % of sales revenue is earned by 20% of firm’s products• 20 % of the items in a factory Store may account for 80 % of

the volume of items issued• 80 % of defects are caused by 20% of the possible defects

type

• Also used in conjunction with Brainstorming, Cause and Effect Analysis and Cumulative Line Chart. The Diagram displays, in decreasing order, the relative contribution of each cause or problem to the total

• The relative contribution can be based on the number of occurrences, the quality damage or the cost associated with each cause or problem

How to create a Pareto Diagram 1/2

Types of Defects Number of Defects A-Lever Tight 10B-W/High 42C-Less Torque 6D-Pause Fail 104E-Abnormal noise 4F-Auto Stop Fail 20G-Others 14

1 2 3

4

Types of Defects Number of Defects D-Pause Fail 104B-W/High 42F-Auto Stop Fail 20G-Others 14A-Lever Tight 10C-Less Torque 6E-Abnormal noise 4

200

Types of Defects No.of Defects Cumulative Total

D-Pause Fail 104 104B-W/High 42 146F-Auto Stop Fail 20 166G-Others 14 180A-Lever Tight 10 190C-Less Torque 6 196E-Abnormal noise 4 200

200

Types of Defects Number of Defects Cumulative Total % Cumulative D-Pause Fail 104 104 52B-W/High 42 146 73F-Auto Stop Fail 20 166 83G-Others 14 180 90A-Lever Tight 10 190 95C-Less Torque 6 196 98E-Abnormal noise 4 200 100

200

D-Pause

Fail

B-W/H

igh

F-Auto St

op Fail

G-Others

A-Leve

r Tigh

t

C-Less

Torq

ue

E-Abnorm

al noise

020406080

100104

4220 14 10 6 4

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Number of Defects

0102030405060708090

100104

42

2014 10 6 4

Number of Defects % Cumulative

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0102030405060708090

100

0102030405060708090100

104

42

2014 10 6 4

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7383

9095 98 100

Number of Defects % Cumulative

7

How to create a Pareto Diagram 2/2

Pareto Diagram

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Number of Defects % Cumulative

No. of Defects

Types of Defects

Cause & Effect Diagram 1/2• It is called Fish-Bone Diagram due to the shape of the completed

structure.• This was proposed by Kaoru Ishikawa in the 1960s,hence also

referred as Ishikawa Diagram • The Ishikawa diagram shows the causes of a certain event. A

common use of the Ishikawa diagram is in product design, to identify potential factors causing an overall effect

• It shows the relation between a quality characteristics and factors• Causes in the diagram are often based on a certain set of causes,

such as the 5M+1E,8 P's or 4 S's• Cause-and-effect diagrams can reveal key relationships among

various variables, and the possible causes provide additional insight into process behaviour.

Cause & Effect Diagram 2/2• Causes in a typical diagram are normally grouped into categories,

the main ones of which are:• The 5M+1E- recommended for the manufacturing industryMachine, Method, Materials, Measurement, Men and Environment• The 8 P's - recommended for the administration and service

industriesPrice, Promotion, People, Processes, Place / Plant, Policies, Procedures, and Product (or Service)• The 4 S's - recommended for the service industrySurroundings, Suppliers, Systems, Skills • Causes should be specific, measurable, and controllable derived

from brainstorming sessions. Then causes should be sorted through affinity-grouping to collect similar ideas together. These groups should then be labeled as categories of the fishbone.

Structure of Cause-and-effect Diagram

Procedure for making C&E diagram

STEP 1:• Determine the Pain point/ characteristicSTEP 2:• Draw in the backbone from left to right, and enclose the characteristic in a square• Next, write the primary causes which affect the characteristics as big bones also enclosed by squaresSTEP 3:• Write the causes (Secondary Causes) which affect the big bones (Primary Causes) as medium sized bones• Write the causes (Territory Causes) which affect the medium sized bones as small bones.

STEP 4:

• Assign an importance to each factor, and mark the particularly important factors that seem to have a significant effect on the quality characteristics.

STEP 5:

• Record any necessary information

Conti…

Example of C&E Analysis

Histogram 1/2

• Histogram is a graphical technique to represent dispersion of data

• Ideally it will have symmetrical shape tapering away on both sides from target value

• For E.g 1. Production from same production line usually differs slightly

in dimensions, hardness, or others qualities2. when we commute to work every day, the time required

varies from one day to otherThus , Histogram can be used to • To find out if the lot has acceptance dispersion• To compare with target value and specification limits to

identify special causes of variation

• Histogram is a graph that represents the class frequencies by vertical adjacent rectangles in a frequency distribution.

• In a histogram, the magnitude of the class interval is plotted along the horizontal axis and the frequency on the vertical axis

• Since each class has lower and upper values, hence two equal vertical lines represent the frequency.

• Upper ends of the two lines representing the class interval are joined together. The height of rectangle thus obtained are proportional to their frequencies.

Histogram 2/2

Methodology for drawing Histogram

1 2How to calculate frequency in Excel1. Select the cell2. Go to Formulas/More

Functions/ Statistical/Frequency

3. Select the Data & Bin limits

4. You will have the frequency

5. Select the cell range of FREQ equal to BIN LIMITS 6. Go to Formula Bar in Excel

and press ctrl+shift+enter7. You will have FREQ for defined range

STUDENT %A 47B 45C 78D 82E 89F 45G 55H 65I 58J 68K 52L 57M 89N 35O 65P 58Q 50R 52S 73T 62U 59V 65W 68X 84Y 82Z 80

STUDENT % BIN LIMITS FREQUENCYA 47 0 0B 45 5 0C 78 10 0D 82 15 0E 89 20 0F 45 25 0G 55 30 0H 65 35 1I 58 40 0J 68 45 2K 52 50 2L 57 55 3M 89 60 4N 35 65 4O 65 70 2P 58 75 1Q 50 80 2R 52 85 3S 73 90 2T 62 95 0U 59 100 0V 65W 68X 84Y 82Z 80

HISTOGRAM

Almost a TWIN PEAK

Case

3. Draw the Bar graph and set the limits. You will have a histogram

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 1000

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Histogram- Student's Performance

FREQUENCY

Bin limits

Freq

uenc

y

Types of histograms

A. General Type

G. Comb Type

C. Positively skew Type D. Left hand precipice type

E. Plateau Type F. Twin-peak Type

B. Isolated-peak Type

Control Charts 1/2• Variability is inherent in all manufacturing processes. These

variations may be due to two causes :i. Random / Chance causes (un-preventable)ii. Assignable causes (preventable)• Control charts was developed by Dr. Walter A. Shewhart during

1920's while he was with Bell Telephone Laboratories.• These charts separate out assignable causes.• Control chart makes possible the diagnosis and correction of

many production troubles and brings substantial improvements in the quality of the products and reduction of spoilage and rework.

• It tells us when to leave a process alone as well as when to take action to correct trouble

• Control chart is a chart to examine whether a process is in a stable condition.

• The control limits are drawn for the process characteristics to be controlled.

• Data is of two types :1. Variable - measured and expressed quantitatively2. Attribute - qualitative• The elements of a control chart- Mean is the average of a sub-groupR - Range is the difference between the minimum and maximum in a sub-group1. CL - Center line: This is the expected mean of the process2. UCL - Upper Control Limit and3. LCL - Lower Control Limit These are limit to maximum expected variation of the process.

Control Charts 2/2

1 2 3 4 5

Target

Lower control line

Upper warning line

Lower warning line

Sample Number

Upper control line

Lower control line

Sam

ple

Sta

tistic

sControl Chart

24

Interpreting Control Chart

UCL

1 2 3 4 5 6 7 8

Sample Number

Sta

tistic

s

UWL

LCL

LWL

One point outsidecontrol limit

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Interpreting Control Chart

UCL

1 2 3 4 5 6 7 8

Sample Number

Sta

tistic

s

UWL

LCL

LWL

Two points out of three consecutive points between warning limit and corresponding control limit

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Interpreting Control Chart

UCL

1 2 3 4 5 6 7 8

Sample Number

Sta

tistic

s

UWL

LCL

LWL

Two consecutive points between warning limit and corresponding control limit

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Interpreting Control Chart

UCL

1 2 3 4 5 6 7 8

UWL

LCL

LWL

Seven consecutive points on one side of the centre line

Sample Number

Sta

tistic

s

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Interpreting Control Chart

UCL

1 2 3 4 5 6 7 8

Sample Number

Sta

tistic

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UWL

LCL

LWL

Seven consecutive points having upward trend

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Interpreting Control Chart

UCL

1 2 3 4 5 6 7 8Sample Number

Sta

tistic

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UWL

LCL

LWL

Seven consecutive points having downward trend

Scatter Diagram 1/2

• A relationship may or may not exist between two variables• If a relationship exists, it may be positive or negative, it may

be strong or weak and may be simple or complex• A tool to study the relationship between two variables is

known as Scatter Diagram• Examples:• The relationship between moisture content in threads and

elongation.• The relationship between an Ingredient and Product

Hardness.• The relationship between cutting speed and variations in the

length of parts.

• The method consists of plotting the two series on a graph and fitting a Line of Best Fit free hand

• The direction of line shows the extent of correlation. If the line goes upward from left to right, it means the correlation is positive.

• If the line goes downward from left to right, it means the correlation is negative.

• If the points on the plot are scattered largely, it shows little or no correlation.

• Although Scatter Diagrams are very convenient tools for asserting two-way relationships, they don’t provide formal measures of these relationships.

• Scatter Diagrams also don’t provide any means of establishing whether any apparent associations are actually due to chance or not.

Scatter Diagram 2/2

How to draw scatter diagram

Year Average Sales (Lac) Profits (Lac)

1987 168 661988 182 701989 192 761990 235 921991 304 1171992 304 1321993 333 1471993 343 1511994 423 1591995 484 1701996 553 1881997 548 1861998 589 2041999 639 2232000 661 234

1

1. Select the Sales & Profit column and insert a Scatter chart

2. Add the axis label & Trend line

2

100 200 300 400 500 600 7000

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Sales vs. profit

Profits (Lac)Linear ( Profits (Lac))

Avg. Sales (Lacs)

Profi

ts (L

acs)

3Strong

Positive correlation

Y Y

YY

Y

XXX

XX

Positive correlation Positive correlation may be present

No correlation

Negative correlation may be present

Negative correlation present

Various plot patterns of scatter diagrams

X

Y

Strong CurvilinearAssociation

Flow chart 1/2Purpose:Visual illustration of the sequence of operations required to complete a task• To develop understanding of how a process is done• To study a process for improvement• To communicate to others how a process is done• When better communication is needed between people involved with the

same process• To document a process• When planning a projectBenefits:

• Identify process improvements• Understand the process• Shows duplicated effort and other non-value-added steps • Clarify working relationships between people and organizations • Target specific steps in the process for improvement.

Benefits• Show what actually happens at

each step in the process • Show what happens when non-

standard events occur • Graphically display processes to

identify redundancies and other wasted effort

How is it done?• Write the process step inside

each symbol• Connect the Symbols with

arrows showing the direction of flow

Toolbox

Flow chart 1/2

Check sheet

WHAT IS A CHECK SHEET ?

A Check Sheet is a method for collecting the right data in a simple manner.

Classification of check sheets according to functions:

1. Recording check sheet

(A) Defective Item Check Sheet(B) Defective Cause Check Sheet(C) Production process distribution Check Sheet2. Inspection Check sheet(A) Check up Confirmation Check Sheet(B) Evaluation item inspection Check Sheet

How to make check sheet1. Clearly indicate the purpose of the data collection2. Decide on how to collect data3. Estimate the total quantum of data4. Decide on the Check Sheet form5. Enter the data and draw up the Check Sheet.6. Check if it meet the objectives. Is it easy to record? If there

are any improvement points, freely amend it.Reading and using the check sheet:A) Read the whole pictureB) To see the time series of time, day and monthC) Tie-up the use of other tools

1. Defective Item Check Sheet for a motor

Recording check sheet 1/2

3. Production process distribution Check

Sheet

2. Defective Cause Check Sheet

Recording check sheet 2/2

INSPECTION CHECK SHEET1. Check up Confirmation Check Sheet

2. Evaluation item inspection Check Sheet

To sum up 7 QC tools ,they are used to

Tools ResultPareto Diagram To Identify the major cause/issue

Cause and Effect Diagram

To identify the cause and effect relationship

Histogram To see the distribution of dataControl Charts To find out abnormalities and identify the

current status

Scatter Diagrams To identify the relationship between two things

Flow chart illustration of the sequence of operations required to complete a task

Check Sheets To record data collection

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