7QC Tools
Q7T/PPT- 1
7 QC TOOLS7 QC TOOLS
7QC Tools
Q7T/PPT- 2
Types of 7QC toolsCheck SheetCheck Sheet
Pareto DiagramPareto Diagram
Cause & Effect diagramCause & Effect diagram
StratificationStratification
Scatter DiagramScatter Diagram
Graph &Control chartsGraph &Control charts
HistogramHistogram
7 QC Tools7 QC Tools
Types
7QC Tools
Q7T/PPT- 3
Check sheetCheck sheetCheck sheet
7QC Tools
Q7T/PPT- 4
What is a check sheet?
Why is a check sheet necessary?
Check sheet
7QC Tools
Q7T/PPT- 5
Check sheets are forms used for
• standardizing
• checking results of work
• verifying and collecting data
Check sheet
Check sheet
7QC Tools
Q7T/PPT- 6
Check Sheet
Measured Data
Measured Data
Counted Data
Counted Data
Primary Data
Primary Data
Point Scale Data
Point Scale Data
Ordered Data
Ordered Data
Indiscrete value such as height, weight, length, time & temp., Etc.Indiscrete value such as height,
weight, length, time & temp., Etc.
Discrete value such as no. Of recording errors, no. of Item sold
& Rejections etc.
Discrete value such as no. Of recording errors, no. of Item sold
& Rejections etc.
YES / NO or √ / X - Type
YES / NO or √ / X - Type
1st, 2nd Order …Very Good, Good, No Good
… - Type
1st, 2nd Order …Very Good, Good, No Good
… - Type
1 Point, 2 Point … etc.
1 Point, 2 Point … etc.
Types of Check SheetCheck sheet
7QC Tools
Q7T/PPT- 7
Defect check sheet
Check sheet
Example of check sheet
Month ,dayComponent
12345678
9
10
4/1 2 3 4
No. of No. of defectsdefects
7QC Tools
Q7T/PPT- 8
• Clarifying the objective• Determining the type of check sheet to
use• Deciding which items to check• Creating the check sheet• Recording the data• Tallying the data• Examining the check sheet
How to prepare check sheets?
7QC Tools
Q7T/PPT- 9
Below items can be added , as necessary
1. The purpose of the checks
2. The items being checked
3. The methods of the checks
4. The dates and times of the checks
5. The person to perform the checks
6. The results
Check points for check sheets preparationCheck sheet
7QC Tools
Q7T/PPT- 10
Pareto diagramPareto diagram
Pareto
7QC Tools
Q7T/PPT- 11
Do you remember this? (14th March 2001 - Eden gardens )
Pareto
7QC Tools
Q7T/PPT- 12
Do you remember this? (14th March 2001 - Eden gardens )
Pareto
7QC Tools
Q7T/PPT- 13
Now let’s look at the second innings score board:IndiaSS Das hit wicket b Gillespie 39S Ramesh c ME Waugh b Warne 30VVS Laxman c Ponting b McGrath 281SR Tendulkar c Gilchrist b Gillespie 10SC Ganguly c Gilchrist b McGrath 48R Dravid run out 180N R Mongia b McGrath 4Zaheer Khan not out 23Harbhajan Singh not out 8
Total 657
Pareto
7QC Tools
Q7T/PPT- 14
When we observe which batsmen got the maximum runs we can see that Laxman & Dravid got 461 out of the 657 runs. That is about 70% of the runs.
22% of the 9 batsmen who batted got 70% of the runs!
Let’s now observe the Australian 2nd innings score card
Pareto
7QC Tools
Q7T/PPT- 15
AustraliaM Hayden lbw b Tendulkar 67M Slater c Ganguly b Harbhajan 43J Langer c Ramesh b Harbhajan 28M Waugh lbw b Raju 0S Waugh c Sub B Harbhajan 24R Ponting c Das b Harbhajan 0A Gilchrist lbw b Tendulkar 0J Gillespie c Das b Harbhajan 6S Warne lbw b Tendulkar 0M Kasprowicz not out 13G McGrath lbw b Harbhajan 12
Total 212
Pareto
7QC Tools
Q7T/PPT- 16
Who got the wickets?
O M R W
Zaheer Khan 8 4 30 0
V Prasad 3 1 7 0
Harbhajan Singh 30.3 8 73 6
V Raju 15 3 58 1
S Tendulkar 11 3 31 3
S Ganguly 1 0 2 0
Pareto
7QC Tools
Q7T/PPT- 17
When we observe which bowlers got the maximum wickets we can see that Harbhajan & Tendulkar got 9 out of the 11 wickets. That is about 80% of the wickets.
30% of the 6 bowlers who bowled got 80% of the wickets!
This illustrates the Pareto principle
Pareto
7QC Tools
Q7T/PPT- 18
• Vilfredo Pareto was an Italian engineer in the 19th Century who studied the number of people in various income classes & declared
‘’20% of the people own 80% of the country’s wealth;
80% of the people own 20% of the country’s wealth”
Pareto
Pareto
7QC Tools
Q7T/PPT- 19
Pareto Principle
Pareto principle holds good to the present day in various applications
‘ A few causes lead to many defects;
many causes lead to few defects.’
The few causes that lead to many defects are the vital few.
The many causes that lead to few defects are the trivial many.
Pareto
7QC Tools
Q7T/PPT- 20
“Get to the biggest problems first”
‘Solve the vital few’
Pareto
7QC Tools
Q7T/PPT- 21
REMEMBER …The most frequent or most costly events are not always the most important.
e.g.Two fatal accidents deserve more attention than 100 cut fingers.
7QC Tools
Q7T/PPT- 22
1. Collect data
2. Arrange data in the descending order
3. Calculate the relative % for individual data
4. Calculate the cumulative % for individual data
5. Draw a graph with scales on both axis
6. Draw bar chart based on data
7. Using cumulative % data, draw cumulative curve
8. Identify the VITAL FEW (thumb rule > 70%)
66
45
20 15 12 10 8 6 5 4 4 2 2 1
33
55.5
65.5
7379
8488
91 93.5 95.5 97.5 98.5 99.5 100
0
25
50
75
100
125
150
175
200
Mat
eria
ls
Mar
ketin
g
Pla
ntM
aint
enan
ce
Fina
nce
Ser
vice
Pro
duct
ion
Eng
inee
ring
Per
sonn
el
Info
rmat
ion
Sys
tem
s
Sto
res
Rese
arch
&D
evel
opm
ent
Oth
ers
Qua
lity
Fact
ory
prod
uctio
n
Man
ufac
turin
gP
lann
ing
Dept
In n
os
0
25
50
75
100
In %
Pareto
Creating a Pareto Diagram
Steps
7QC Tools
Q7T/PPT- 23
Data collection through check sheetPeriod : Week No. 45 To 50No. Of External Phone Calls
4Others146Information & Systems134Research & Development1215Finance1166Materials108Personnel95Stores81Manufacturing Planning72Factory production620Plant Maintenance545Marketing412Service32Quality 210Production Engineering 1
No. Of cells regd.DepartmentSl.No
STEP 1 66
45
20 15 12 10 8 6 5 4 4 2 2 1
33
55.5
65.5
7379
8488
91 93.5 95.5 97.5 98.5 99.5 100
0
25
50
75
100
125
150
175
200
Mat
eria
ls
Mar
ketin
g
Pla
ntM
aint
enan
ce
Fina
nce
Ser
vice
Pro
duct
ion
Eng
inee
ring
Per
sonn
el
Info
rmat
ion
Sys
tem
s
Sto
res
Rese
arch
&D
evel
opm
ent
Oth
ers
Qua
lity
Fact
ory
prod
uctio
n
Man
ufac
turin
gP
lann
ing
Dept
In n
os
0
25
50
75
100
In %
Pareto
7QC Tools
Q7T/PPT- 24
200
1Manufacturing Planning142Factory production132Quality124Others114Research & Development105Stores96Information Systems88Personnel710Production Engineering 612Service515Finance420Plant Maintenance345Marketing266Materials1
No. Of cells reqd.DepartmentSl.No
66
45
20 15 12 10 8 6 5 4 4 2 2 1
33
55.5
65.5
7379
8488
91 93.5 95.5 97.5 98.5 99.5 100
0
25
50
75
100
125
150
175
200
Mat
eria
ls
Mar
ketin
g
Pla
ntM
aint
enan
ce
Fina
nce
Ser
vice
Pro
duct
ion
Eng
inee
ring
Per
sonn
el
Info
rmat
ion
Sys
tem
s
Sto
res
Rese
arch
&D
evel
opm
ent
Oth
ers
Qua
lity
Fact
ory
prod
uctio
n
Man
ufac
turin
gP
lann
ing
Dept
In n
os
0
25
50
75
100
In %
Pareto
STEP 2 Arrange data in the descending orderNo. Of External Phone Calls
7QC Tools
Q7T/PPT- 25
2000.51.01.02.02.02.53.04.05.06.07.510.022.533.0
Relative %
1Manufacturing Planning142Factory production132Quality124Others114Research & Development105Stores96Information Systems88Personnel710Production Engineering 612Service515Finance420Plant Maintenance345Marketing266Materials1
Nos.DepartmentSl.No
66
45
20 15 12 10 8 6 5 4 4 2 2 1
33
55.5
65.5
7379
8488
91 93.5 95.5 97.5 98.5 99.5 100
0
25
50
75
100
125
150
175
200
Mat
eria
ls
Mar
ketin
g
Pla
ntM
aint
enan
ce
Fina
nce
Ser
vice
Pro
duct
ion
Eng
inee
ring
Per
sonn
el
Info
rmat
ion
Sys
tem
s
Sto
res
Rese
arch
&D
evel
opm
ent
Oth
ers
Qua
lity
Fact
ory
prod
uctio
n
Man
ufac
turin
gP
lann
ing
Dept
In n
os
0
25
50
75
100
In %
Pareto
STEP 3 Calculate the relative % for individualNo. Of External Phone Calls
7QC Tools
Q7T/PPT- 26
100200100.099.598.597.595.593.591.088.084.079.073.065.555.533.0
Cumulative %
0.51.01.02.02.02.53.04.05.06.07.510.022.533.0
Relative %
1Manufacturing Planning142Factory production132Quality124Others114Research & Development105Stores96Information Systems88Personnel710Production Engineering 612Service515Finance420Plant Maintenance345Marketing266Materials1
Nos.DepartmentSl.No
66
45
20 15 12 10 8 6 5 4 4 2 2 1
33
55.5
65.5
7379
8488
91 93.5 95.5 97.5 98.5 99.5 100
0
25
50
75
100
125
150
175
200
Mat
eria
ls
Mar
ketin
g
Pla
ntM
aint
enan
ce
Fina
nce
Ser
vice
Pro
duct
ion
Eng
inee
ring
Per
sonn
el
Info
rmat
ion
Sys
tem
s
Sto
res
Rese
arch
&D
evel
opm
ent
Oth
ers
Qua
lity
Fact
ory
prod
uctio
n
Man
ufac
turin
gP
lann
ing
Dept
In n
os
0
25
50
75
100
In %
Pareto
STEP 4 Calculate the cumulative % for individualData No. Of External Phone Calls
7QC Tools
Q7T/PPT- 27
100200100.099.598.597.595.593.591.088.084.079.073.065.555.533.0
Cumulative %
0.51.01.02.02.02.53.04.05.06.07.510.022.533.0
Relative %
1Manufacturing Planning142Factory production132Quality124Others114Research & Development105Stores96Information Systems88Personnel710Production Engineering 612Service515Finance420Plant Maintenance345Marketing266Materials1
Nos.DepartmentSl.No
TRIVIAL MANY
VITAL FEW
Pareto
7QC Tools
Q7T/PPT- 28
10020010073.065.555.533.0
Cumulative %
277.510.022.533.0
Relative %
60Others515Finance420Plant Maintenance345Marketing266Materials1
Nos.DepartmentSl.No
Pareto
7QC Tools
Q7T/PPT- 29
Pareto
66
45
20 15
54
0
30
60
90
120
150
180
Mat
eria
ls
Mar
ketin
g
Pla
nt M
aint
enan
ce
Fina
nce
othe
rs
Dept
In n
os
7QC Tools
Q7T/PPT- 30
66
45
20 15
5433
55.5
65.5
73
100
0
30
60
90
120
150
180
Mat
eria
ls
Mar
ketin
g
Pla
nt M
aint
enan
ce
Fina
nce
othe
rs
Dept
In n
os
0
25
50
75
100
Cum
ulat
ive
%
Pareto
7QC Tools
Q7T/PPT- 31
Pareto
66
45
2015
5433
55.5
65.5
73
100
0
30
60
90
120
150
180
Mat
eria
ls
Mar
ketin
g
Pla
ntM
aint
enan
ce
Fina
nce
othe
rs
Dept
In n
os
0
25
50
75
100
Cum
ulat
ive
%
VitalFew
70 %
7QC Tools
Q7T/PPT- 32
• To Clearly prioritise the magnitude of the problem.
• To identify the vital few and trivial many problems.
• To find 80/20 rule which states that 80% of the
problems are created by 20% of the causes.
Pareto
Why pareto ?
7QC Tools
Q7T/PPT- 33
Add examples from APC………..
7QC Tools
Q7T/PPT- 34
SL# D esc ription O ct '02 Nov '02 D ec '02 Jan '03 Total % D PU C um %1 Sec o n d Pass 520 710 73 759 2062 6 .38 75.972 D efec tive 68 227 22 14 331 1 .02 88. 1 63 B roken C om p 6 48 6 5 65 0 .20 90.564 M is inserted 1 22 1 7 31 0 . 1 0 91 . 705 Skewed C om p 6 14 1 3 24 0 .07 92.586 C om p M issing 15 0 0 4 1 9 0 .06 93.287 O ut of to le ranc e 8 7 0 4 1 9 0 .06 93.988 N o / Low so lder 8 9 0 1 1 8 0 .06 94.649 L ifted 7 2 0 4 1 3 0 .04 95. 1 2
10 Shorts 9 0 0 0 9 0 .03 95 .5Tested 8612 14314 1185 12859 36970P assed 7838 13219 1058 11978 34093 8 .4 8 .02
Q 4' 02 F inal failu re D etails
Q 4 F in a l F a i lu re D eta i ls
2062
331
65 31 24 19 19 18 13 9
75.97
88.16 90.56 91.70 92.58 93.28 93.98 94.64 95.12 95.5
0
500
1000
1500
2000
2500
1 2 3 4 5 6 7 8 9 10Failure
Qty
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
Cum %
Q4 ‘02 Final Failure Details
Data Collection
7QC Tools
Q7T/PPT- 35
You have to cut down your house expenditure by 20% / month
How will you do it ?
Pareto
Same problem, but different approach…
ParetoPareto
7QC Tools
Q7T/PPT- 36
Make a check list of all the expenses in your home & the amount you
spend on these expenses
Pareto
7QC Tools
Q7T/PPT- 37
1300Petrol16
500Insurance Premium13
200Clothes15
300Others17
0Loan repayment14
200Hospital121500Educational11200Travel101500Entertainment & Lifestyle92000Groceries8150Maid servant7300Milkman6120News paper bill5210Cable TV Bill4280Water Bill3500Electricity Bill23000House Rent 1
AmountExpenseSl.No
Pareto
7QC Tools
Q7T/PPT- 38
Arrange these expenses & amounts in an order, with the highest
expense being the first & lowest expense being the last
Pareto
7QC Tools
Q7T/PPT- 39
150Maid servant15
120News paper16
300Others9
12260
0Loan repayment17
200Hospital14200Clothes13200Travel12210Cable TV11280Water bill10
300Milkman8500Insurance premium7500Electricity bill6
1300Petrol51500Educational41500Entertainment32000Groceries23000House rent1
AmountExpenseSl.No
Pareto
7QC Tools
Q7T/PPT- 40
Calculate the percentage contribution of each of these expenses.
Percentage can be calculated by the formula
Individual expense
Total expenseX 100
Pareto
7QC Tools
Q7T/PPT- 41
1.63200Hospital14
1.22150Maid servant15
0.98120Newspaper16
100122600
1.631.631.722.282.452.454.084.0810.6
12.2312.2316.3224.47
Relative %
0Loan repayment17
200Clothes13
200Travel12
210Cable TV11
280Water bill10
300Others9
300Milkman8
500Insurance premium7
500Electricity bill6
1300Petrol5
1500Educational4
1500Entertainment3
2000Groceries2
3000House rent1
Nos.DepartmentSl.No
Pareto
7QC Tools
Q7T/PPT- 42
1000.98120Newspaper16
99.021.22150Maid servant15
97.81.63200Hospital14
10010012260100.0
96.1794.5492.9191.1988.9186.4684.0179.9375.8565.2553.0240.7924.47
Cumulative %
0
1.631.631.722.282.452.454.084.0810.6
12.2312.2316.3224.47
Relative %
0Loan repayment17
200Clothes13
200Travel12
210Cable TV11
280Water bill10
300Others9
300Milkman8
500Insurance premium7
500Electricity bill6
1300Petrol5
1500Educational4
1500Entertainment3
2000Groceries2
3000House rent1
Nos.DepartmentSl.No
Pareto
7QC Tools
Q7T/PPT- 43
1000.98120Newspaper16
99.021.22150Maid servant15
97.81.63200Hospital14
10010012260100.0
96.1794.5492.9191.1988.9186.4684.0179.9375.8565.2553.0240.7924.47
Cumulative %
0
1.631.631.722.282.452.454.084.0810.6
12.2312.2316.3224.47
Relative %
0Loan repayment17
200Clothes13
200Travel12
210Cable TV11
280Water bill10
300Others9
300Milkman8
500Insurance premium7
500Electricity bill6
1300Petrol5
1500Educational4
1500Entertainment3
2000Groceries2
3000House rent1
Nos.DepartmentSl.No
7QC Tools
Q7T/PPT- 44
0
2000
4000
6000
8000
10000
12000
House R
ent
Grocerie
sEnte
rtainm
ent
Educa
tiona
l
Petrol
Others
Expenses
Amou
nt
0102030405060708090100
Cum
ulat
ive
%
7QC Tools
Q7T/PPT- 45
Cause & Effect Cause & Effect diagramdiagram
Cause & effect diagram
7QC Tools
Q7T/PPT- 46
• To identify and systematically list the different causes
that can be attributed to a problem (or an effect)
• To identify the reasons why a process goes out of
control
• To decide which causes to investigate for process
improvement.
Why Cause & Effect ?Cause & effect diagram
7QC Tools
Q7T/PPT- 47
What is Effect ?
EFFECT = A Result or an outcome
EFFECT is What happens
Cause & effect diagram
7QC Tools
Q7T/PPT- 48
What is cause ?
CAUSE = Reason or Factor contributing to the EFFECT
CAUSE is WHY it happens
Cause & effect diagram
7QC Tools
Q7T/PPT- 49
The analysis of “why?” for “what?”
is cause and effect diagram
Cause & effect diagram
7QC Tools
Q7T/PPT- 50
In 1953, Kaoru Ishikawa, Professor of the University of Tokyo, used the Cause & effect diagram for the first time.A cause & effect diagram is also called a fish bone diagram since it looks like the skeleton of a fish.
Cause & effect diagram
7QC Tools
Q7T/PPT- 51
Pareto chart
Cause-and-effect diagram
Cause & Effect diagram derived from pareto
Cause & effect diagram
7QC Tools
Q7T/PPT- 52
Steps of making cause & effect diagram
Cause & effect diagram
7QC Tools
Q7T/PPT- 53
Steps of making cause & effect diagramCause & effect diagram
Step 0 • Gather members for discussion • Clarify the problem to all members Step 1 • Conduct Brain storming session• List all possible causes Step 2
• Classify the causes into 4M • Draw Ist level Cause & Effect diagramStep 3 • Delete irrelavant causes Step 4• Assign importance factor to the remaining causesStep 5 • Conduct why why analysis if required to find root causes
7QC Tools
Q7T/PPT- 54
Cause & effect diagram
Step 1
List all the causes that have been suggested by team members as a part of brain storming.
What is brain storming ?
7QC Tools
Q7T/PPT- 55
Brainstorming is another tool which we use as a part of all the 7 QC tools
7QC Tools
Q7T/PPT- 56
BRAIN STORMING !
Brain storming
7QC Tools
Q7T/PPT- 57
BRAIN STORMING
Brain storming is a technique to obtain creative ideas from a group of persons in a shortest possible time
Brain storming plays an important role to build a cause and effect diagram
WHY To identify the problem - to identify the causes
To find solution - to prevent problem
Brain storming
7QC Tools
Q7T/PPT- 58
BRAIN STORMING
Brain storming can be conducted in two ways
1. Structured
• Every person in a group must give an idea as their turn arises.
• Forces even shy people to participate.
• Creates a certain amount of pressure to contribute.
Brain storming
7QC Tools
Q7T/PPT- 59
2. Unstructured
• Group members simply give ideas as they come to mind.
• Creates more relaxed atmosphere
• Risks domination.
Thumb rule : 5 – 15 minutes works well
Brain storming
7QC Tools
Q7T/PPT- 60
BRAIN STORMING SESSION• Let all the members speak freely and give ideas
• Encourage wild ideas
• “Quantity” rather than “Quality” ideas
• Suspend judgment on “Good” or “Bad”
• Ride on another’s ideas
• Never criticize other persons’ opinions
• Never prohibit a person from speaking
• See the problem from different angles/facets
• Write down all the viewpoints
• List the cause/ideas
• Think of the countermeasures to eliminate the causes
• Leader/facilitator need to guide the members in generating ideas
• Whenever necessary non – members can also be involved
Brain storming
7QC Tools
Q7T/PPT- 61
WHY BRAIN STORMING?
TO IDENTIFY THE PROBLEM
TO IDENTIFY CRITICAL CAUSES
TO FIND THE SOLUTION
TO PREVENT THE PROBLEM
Brain storming
7QC Tools
Q7T/PPT- 62
BENEFITS OF BRAIN STORMING?
Brain storming
• Individual is limited in generating ideas and that
group produces more ideas
• Ideas are improved upon by members
• Presence of others increases creativity
• Pooling of ideas and resources is made possible by
coming together as a group
• Individual is limited in generating ideas and that
group produces more ideas
• Ideas are improved upon by members
• Presence of others increases creativity
• Pooling of ideas and resources is made possible by
coming together as a group
7QC Tools
Q7T/PPT- 63
Cause & effect diagram
Step 2
Draw Cause & Effect diagram – Level 1
Classify the causes into 4M
Sort out the relations among the causes & connect the sub causes to the main causes. The main causes should then be connected to the effect.
7QC Tools
Q7T/PPT- 64
MATERIALMETHOD
MAN MACHINE
Sub cause
Sub-sub cause
CAUSES EFFECT
PROBLEM
7QC Tools
Q7T/PPT- 65
Cause & effect diagram
MACHINEMAN
MATERIAL METHOD
Fatigue
Dimensional Variation
Location
JIGS & FIXTURES
STABILITY
INSPECTION
Method
Attentiveness
SPIRIT
Experience
HEALTH
SKILL
Storage
QUALITY
Inspection
ShapeFORM
Dimension
Feed
WORKING
Spindle speed
Illness Training
ConcentrationInstrument
Clamping
Imbalance
Vibration
SETTING
Degree of tightening
Placement on locator
2
7QC Tools
Q7T/PPT- 66
Cause & effect diagram
Step 3
Delete irrelavant causes
7QC Tools
Q7T/PPT- 67
Cause & effect diagram
MACHINEMAN
MATERIAL METHOD
Fatigue
Dimensional Variation
Location
JIGS & FIXTURES
STABILITY
INSPECTION
Method
Attentiveness
SPIRIT
Experience
HEALTH
SKILL
Storage
QUALITY
Inspection
ShapeFORM
Dimension
Feed
WORKING
Spindle speed
Illness Training
ConcentrationInstrument
Clamping
Imbalance
Vibration
SETTING
Degree of tightening
Placement on locator
2
The EFFECT or PROBLEM is stated on the right side of the diagramand the major INFLUENCES or CAUSES are listed to the left.
7QC Tools
Q7T/PPT- 68
Cause & effect diagram
Step 4
Evaluate the siginificance of each cause to the problem and assign importance factor
Assign an importance to each factor, & mark the particularly important factors which seem to have a significant effect.
7QC Tools
Q7T/PPT- 69
Cause Verification
4M Cause Specification Investigation Analysis
Man No focused training Functionwise training
Generic
No method to measure operator's skills
Skill matrix for each workmen
No skill matrix
No OJTPractical training at genba
No OJT
Workmen not trained in specific jobs
Need based training
Common module given
MaterialModule content is academic oriented
Content should be specific need based
Theory based
Method
7QC Tools
Q7T/PPT- 70
Cause & effect diagram
Step 5
Do why why analysis for the significant causes
Atleast ask why 3 times
7QC Tools
Q7T/PPT- 71
Why defects?
D
People
1st Why
Plant
PoliciesProcedure
5th Why
C
3rd Why
4th Why
Thorough investigation of causes
2nd Why
Cause & effect diagram
ASK WHY? 5 TIMES
7QC Tools
Q7T/PPT- 72
Examples :- Cylinder does not operate smoothly
Why Answer ActionWhy is opertion not smooth? Strainer clogged. Clean strainer.Why has strainer clogged? Oil was dirty. Drain oil and clean.Why did oil get dirty? Dirt enters tank. Prevent scattering of chips and cutting fluidWhy does dirt get in? Upper plate of tank has hole and gap. Plug hole and gap.Why was hole made? Repair error during maintenance work. Standardize repairs.
Phenomenon(Result)
Cause
Phenomenon(Result)
Cause
Cause
Phenomenon(Result)
Phenomenon(Result)
Primary Secondary
Tertier
‘WHY WHY’ Analysis
7QC Tools
Q7T/PPT- 73
Why Answer ActionDisassemble leaking part.
Why did it leak? Cut in O-ring. Replace O-ring.Why was it cut? Rod has scratch. Remove scratch.
Why was it scratched? Chip was scattered and attached on rod.
Take measure to prevent chips from scattering
Why did chips get attached? Cylinder is located within scattering range of chips. Change cylinder position
Rod cover is not placed. Install cover.Why is rod praced in that Why no cover?
Defective design and installation
Standardize design and installation.
- Oil leaks from cylinder rod each time it operates.
‘WHY WHY’ Analysis
7QC Tools
Q7T/PPT- 74
• Special effort should be made to identify as many
causes as possible
• The ideal method to identify as many causes as
possible would be by brainstorming with the team
members.
• All the ideas/causes suggested by members during
the brainstorming session should be noted however
insignificant they may initially appear. Brainstorming
is a session specially meant for free flow of ideas.
Cause & effect diagram
Guidelines
Remember
7QC Tools
Q7T/PPT- 75
MATERIALMETHOD
MAN MACHINE
Sub cause
Sub-sub cause
CAUSES EFFECT
7QC Tools
Q7T/PPT- 76
COPYING PAPERHANDLING
MACHINE PROCESS CONSUMABLES
Party removed
Dust accumulation
POOR QUALITY
OF XEROX COPIES
Paper shortage
Over consumption
Not using specified quality of paper
Non-standard
Non-standard
Supply from various sources
Wrong paper usage
Paper with stablesLack of knowledge
Not understanding the defect codes/ communicating defects
Nominated persons not handling
Paper jam not cleared properly
Untrained personnel handling the machine
Limited machines
Heavy usage
No cleaning
Location
Frequentchanges Serviced by
unauthorized personsImproper service
No periodical service
No stabilizer
Power
High fluctuation
No communication
Specified toner not filled
Lack of knowledge
7QC Tools
Q7T/PPT- 77
Effect
Causes
1
Cause & effect diagram
7QC Tools
Q7T/PPT- 78
A combination of Pareto diagram & cause and effect diagram is an ideal way to arrive at the main problem & its causes.
Take the biggest problem from the pareto diagram & put it on the right side in the cause & effect diagram.
Derive the causes for the same.
7QC Tools
Q7T/PPT- 79
Examples from APC………..
7QC Tools
Q7T/PPT- 80
Data Mixed process& Original
MANMAN
METHODMETHOD MATERIALMATERIAL
MACHINEMACHINE
PROCESS PROCESS
SCRAPSCRAP
Scrap Disposal Training/Procedure is inadequate
Machine rejectionsare high.
No process flow
Improper Handling
Handling Pro not defined.
Incoming material.
Improper Storage
Improper /Movement
High Rej in M/C.
Improper StorageIn racks .
No Awareness
Inadequate Training
Improper tools
Program /Nozzleerror
No plan forFeeder maintenance
Identification and SegregationNot done.
No Alarms for M/C Board Jam.
7QC Tools
Q7T/PPT- 81
Data Mixed process& Original
MANMAN
METHODMETHOD MATERIALMATERIAL
MACHINEMACHINE
PROCESS PROCESS
SCRAPSCRAP
Scrap Disposal Training/Procedure is inadequate
Machine rejectionsare high.
No process flow
Improper Handling
Handling Pro not defined.
Incoming material.
Improper Storage
Improper /Movement
High Rej in M/C.
Improper StorageIn racks .
No Awareness
Inadequate Training
Improper tools
Program /Nozzleerror
No plan forFeeder maintenance
Identification and SegregationNot done.
No Alarms for M/C Board Jam.
7QC Tools
Q7T/PPT- 82
LowProductivity
MAN
MATERIAL
METHOD
MACHINE
High Rejection on plastic parts
Scratches
Flow & Black Mark
Printing Defect
Tab & radial BHS problem
GSM error Spindle up
Battery Charging
Operator Skill (Prep of Heat
sink)
Operator absenteeism
Imbalance flow of production
ICT Downtimes and Second pass
High DPU
M/c Cycle time improvement
High Touch up defects before ICT
IC-9 Screening
Serial Number Screening
Board Flow from Wave to ICT
Ishikawa Diagram
7QC Tools
Q7T/PPT- 83
StratificationStratification
Stratification
7QC Tools
Q7T/PPT- 84
Stratification
7QC Tools
Q7T/PPT- 85
Stratification is the act of fine tuning the data in order to
make sure of the significance of the assured factors, to the
grass root level.
Stratification
Stratification
7QC Tools
Q7T/PPT- 86
Why Stratification?
Stratification
To ascertain the difference between different
categories and to analyse the reasons behind
abnormal distribution.
To obtain clues for identifying the causes
7QC Tools
Q7T/PPT- 87
Case studyProblem : Increased Inventory
sheetsBarsTubesImportsProprietarypressingsFastenersRubberRubberBearings
Shop wiseAssy wiseSub-Assy wiseStage wiseMachine wiseRtRejections
Castings
Raw Material
Components
Work in process
Tubes
Proprietary
Fasteners
Bearings
Shop wise
Sub-Assy wise
TotalInventory
Stratification
7QC Tools
Q7T/PPT- 88
Case study 2
Problem : More No. of Accidents
Stratification
Let us stratify the the data regarding the accidents
7QC Tools
Q7T/PPT- 89
STATISTICSSTATISTICS
REPORTABLE ACCIDENTS REPORTABLE ACCIDENTS :: 08 08
NONNON--REPORTABLE ACCIDENTSREPORTABLE ACCIDENTS :: 3333
NEAR MISS INCIDENTSNEAR MISS INCIDENTS :: 2121
LOST TIME INJURIESLOST TIME INJURIES :: 4141
MANDAYS LOSTMANDAYS LOST : : 187187
Rep.acct.Rep.acct. –– Operator not reporting back to duty Operator not reporting back to duty for for more than 48hrsmore than 48hrs
NonNon--reportable acct.reportable acct. –– Operator disablement extending Operator disablement extending beyond beyond the day of shift but the day of shift but less than 48 hrsless than 48 hrs
Lost time injuryLost time injury –– Reportable + NonReportable + Non--reportablereportable
Stratification
7QC Tools
Q7T/PPT- 90
ANALYSIS ANALYSIS ––REPORTABLE ACCIDENTREPORTABLE ACCIDENT
Total no of reportable accident :Total no of reportable accident : 88
Stratification
7QC Tools
Q7T/PPT- 91
ACCORDING TO CATEGORYACCORDING TO CATEGORY
Temp.workman(3)
38%
Regular Employee (4)
49%
Contract Labour (1)
13%
Total no.of Reportable accidents : Total no.of Reportable accidents : 88
Stratification
7QC Tools
Q7T/PPT- 92
ACCORDING TO PROBLEMACCORDING TO PROBLEM
Total no.of Reportable accidents : Total no.of Reportable accidents : 88
0
0
0
0
0
0
0
2
6
0 1 2 3 4 5 6 7
wrong assembly
Contact with chemical
Fall from Two wheeler
Fall from Height
others
Hit by objects/Fallen objects
Hit against object
Wrong handling of material handlingequipment
Adjusting/Cleaning/Loading/Unloadingwhile M/C running
No of Accidents
Stratification
7QC Tools
Q7T/PPT- 93
Total no.of Reportable accidents : Total no.of Reportable accidents : 88
ACCORDING TO BODY PARTS INJUREDACCORDING TO BODY PARTS INJURED
Finger (5)62%
Hand (1)13%
Leg (2)25%
Stratification
7QC Tools
Q7T/PPT- 94
Plant-1 (0)0%
Plant-2 (3)37%
Plant-3 (2)24%
R & D (1)13%
Sp. Wh (1)13%
Others (1)13%
ACCORDING TO PLANTACCORDING TO PLANT
Total no.of Reportable accidents : Total no.of Reportable accidents : 88
Stratification
7QC Tools
Q7T/PPT- 95
Total no.of Reportable accidents : Total no.of Reportable accidents : 88
ACCORDING TO UNITACCORDING TO UNIT
1 1 1
0 0 00
1
2
FAB ENG UNIT PAINT VECH UNIT STORES PLATING
No.o
f acc
iden
ts
PLANTPLANT-- 22
Stratification
7QC Tools
Q7T/PPT- 96
ACCORDING TO SHIFTACCORDING TO SHIFT
4
2 2
0 00
1
2
3
4
5
I II III GEN OT
No.o
f acc
iden
ts
Total no.of Reportable accidents : Total no.of Reportable accidents : 88
Stratification
7QC Tools
Q7T/PPT- 97
ACCORDING TO MONTHACCORDING TO MONTH
0
3
0 0 0 0
2
0
1 1
0
1
0
1
2
3
4
APRIL
MAY
JUNE
JULY
AUGUST
SEPTEM
BER
OCTOBER
NOVEMBER
DECEM
BER
JANUARY
FEBRAUARY
MARCH
No.o
f acc
iden
ts
Total no.of Reportable accidents : Total no.of Reportable accidents : 88
Stratification
7QC Tools
Q7T/PPT- 98
ACCORDING TO FAULTACCORDING TO FAULT
3
2
3
0
1
2
3
4
OPERATORS FAULT SUPERVISORY FAULT SYSTEM ANDENVIRONMENT FAULT
No.o
f acc
iden
ts
Total no.of Reportable accidents : Total no.of Reportable accidents : 88
Stratification
7QC Tools
Q7T/PPT- 99
The data has been stratified
1. According to employee category
2. According to phenomenon
3. According to body parts injured
4. According to plant
a. According to unit
5. According to shift
6. According to month
7. According to fault
Stratification
7QC Tools
Q7T/PPT- 100
Graph & Control charts
Graph&control charts
7QC Tools
Q7T/PPT- 101
Graph&control charts
GraphWhat is Graph?When there are more than 2 interrelated data sets,you writethe datasets on a graph so as to clearly define therelationships.
Why Graph? The details of the data should be• Correctly understood• In their entirety• With just a one look – Pictorial representation
A picture is worth of thousand words
7QC Tools
Q7T/PPT- 102
Graph&control charts
Types of Graphs & Its applicationBar graphs,line graphs, pie charts, and band graphs.There are also other specialty graphs such as radarcharts, Z charts and area graphs
Applications
To understand relative sizes of numbers
To understand trends over time
To understand percent-ages of totals
Graph
7QC Tools
Q7T/PPT- 103
Graph&control charts
Pie chart - Composition of sales turnover 2001-02
Vehicle sales92%
Export Sales1%
Spare parts sales
6%
Other income
1%
Pie charts are used to show percentages or proportions of different components of a specific item.
7QC Tools
Q7T/PPT- 104
Graph&control charts
Bar chart - Sales performance
1417 19 27
4162
83
104133
162184 194
262
0
50
100
150
200
250
300
90-91 91-92 92-93 93-94 94-95 95-96 96-97 97-98 98-99 99-00 00-01 '01-02 '02-03
Rs Million x 100Plan for 2002-03
Bar charts are used for comparing quantities between persons, regions, time intervals etc.
7QC Tools
Q7T/PPT- 105
Graph&control charts
Line chart - Hourly output of Workmen
40
45
42 42 42
43
37
38
39
40
41
42
43
44
45
46
Jan Feb Mar Apr May Jun
No.
of w
o rkm
en
Line graphs are used to depict change or variation over time.
7QC Tools
Q7T/PPT- 106
Graph&control charts
How to draw graphs?
• Select the type of chart or graph most suitable for the type of data.
• Decide the units and scale of items to be shown on X-axis and Y-axis
• Fill the information on the graph
• Join the required points to complete lines or bars.
• Colour or shade the lines or bars to distinguish between different groups or classes.
• Provide appropriate title.
7QC Tools
Q7T/PPT- 107
To add examples from APC
Histogram
7QC Tools
Q7T/PPT- 108
Productivity improvement
208
277246
278
370397
522
0
100
200
300
400
500
600
OCT NOV DEC JAN FEB MARCH APRILMonth
Uni
ts p
rodu
ced
/ Shi
ft
BeforeAfter
Results
7QC Tools
Q7T/PPT- 109
Results
DPU Trend for Cerror Torre
13.912.1 11.9
8.27.3 7.4
6.5
9.98.3
12
7.4
4.4 4.2 3.8
23.8
20.4
23.9
15.6
11.7 11.610.3
0
5
10
15
20
25
30
% D
PUICTFINALDPU
ICT 13.9 12.1 11.9 8.2 7.3 7.4 6.5FINAL 9.9 8.3 12 7.4 4.4 4.2 3.8DPU 23.8 20.4 23.9 15.6 11.7 11.6 10.3
OCT NOV DEC JAN FEB MAR APRIL
Before
After
7QC Tools
Q7T/PPT- 110
Southern chips Problem trend
April
25%
11%26%
16%
22%ScratchesPrinting missingCkt Brkr BrokenSleeve not putWire interchangeWire not connected
7QC Tools
Q7T/PPT- 111
Histogram
Histogram
7QC Tools
Q7T/PPT- 112
It shows the distribution of data
Histogram is an important diagnostic tool which gives a ‘Birds –eye-view’ of the variation in a data set. It is nothing but a frequency distribution chart.
7QC Tools
Q7T/PPT- 113
• In quality control, we try to discover facts by collecting data & then take necessary action based on those facts.
• The data is not collected as an end in itself, but as a means of finding out the facts behind the data.
Histogram
Data
FACTS
7QC Tools
Q7T/PPT- 114
• For example, consider a sampling inspection. We take a sample from a lot, carry out measurements on it, and then decide whether we should accept the whole lot or not. Here our concern is not the sample itself, but the quality of the whole lot.
The totality of items under consideration is called the population.
Histogram
7QC Tools
Q7T/PPT- 115
• The data obtained from a sample serves as a basis for a decision on the population.
• The larger the sample size is, the more information we get about the population.
• But an increase of sample size also means an increase in the amount of data
Histogram
7QC Tools
Q7T/PPT- 116
• It becomes difficult to understand the population from these data even when they are arranged into tables.
• In such a case we need a method which will enable us to understand the population at a glance.
A histogram answers our needs.
Histogram
7QC Tools
Q7T/PPT- 117
Histogram shows a bar chart of accumulated data and provides the easiest way to evaluate the distribution of data .The horizontal axis shows the values of the characteristics, with the region between the largest value and smallest value being broken into several smaller spaces. The sizes of the vertical bars reflects the number of data that fall into these spaces.
Histogram
What is histogram ?
7QC Tools
Q7T/PPT- 118
How to make a histogram?Let us make a histogram using an example.
Histogram
Example:
To investigate the distribution of the diameters of steel shafts produced in the grinding process, the diameters of 90 shafts are measured as shown in the table.
7QC Tools
Q7T/PPT- 119
SampleNumber1 - 10 2.51 2.517 2.522 2.522 2.51 2.511 2.519 2.532 2.543 2.52511 - 20 2.527 2.536 2.506 2.541 2.512 2.515 2.521 2.536 2.529 2.52421 - 30 2.529 2.523 2.523 2.523 2.519 2.528 2.543 2.538 2.518 2.53431 - 40 2.52 2.514 2.512 2.534 2.526 2.53 2.532 2.526 2.523 2.5241 - 50 2.535 2.523 2.526 2.525 2.532 2.522 2.502 2.53 2.522 2.51451 - 60 2.533 2.51 2.542 2.524 2.53 2.521 2.522 2.535 2.54 2.52861 - 70 2.525 2.515 2.52 2.519 2.526 2.527 2.522 2.542 2.54 2.52871 - 80 2.531 2.545 2.524 2.522 2.52 2.519 2.519 2.529 2.522 2.51381 - 90 2.518 2.527 2.511 2.519 2.531 2.527 2.529 2.528 2.519 2.521
Results of Measurement
Diameter after grinding
Histogram
7QC Tools
Q7T/PPT- 120
CONSTRUCTING A HISTOGRAM
STEPS
1. Collect data
2. Determine the largest value & smallest value
3. Obtain the range R (The range is the smallest value in the set of data subtracted from the largest value
4. Divide the range value in to certain number of classes referred to as K
5. Determine the class width, H = R / K
6. Divide the value of class boundary
7. Construct a frequency table, based on the values compiled
8. Construct Histogram based on the frequency table
7QC Tools
Q7T/PPT- 121
STEP 1 Collect data
CASE STUDYPeriod : wk no. 15 to 20Material : ms flange collarUOM : mmThickness : 9 mm + 1.5 mm
9.9 9.3 10.2 9.4 10.1 9.6 10.1 9.9 9.89.8 9.8 10.1 9.9 9.7 9.8 10.0 9.9 9.69.7 9.4 9.6 10.0 9.8 9.9 10.4 10.1 10.010.2 10.1 9.8 10.1 10.3 10.0 9.8 10.2 10.79.9 10.7 9.3 10.3 9.9 9.8 9.5 9.8 9.49.3 10.2 9.2 9.9 9.7 9.9 9.5 9.8 9.49.0 9.5 9.7 9.7 9.8 9.8 9.6 9.3 9.710.0 9.7 9.4 9.8 9.4 9.6 10.3 10.0 9.89.5 9.7 10.6 9.5 10.1 10.0 10.1 9.8 9.39.6 9.4 10.1 9.5 10.1 10.2 9.5 9.8 9.310.3 9.6 9.7 9.7 10.1 9.8 10.0 9.7 10.09.5 9.5 9.8 9.9 9.2 10.0 9.7 10.0 9.79.9 10.4 9.3 9.6 10.2 9.7 9.7 9.7 10.79.9 10.2 9.8 9.3 9.6 9.5 10.7 9.6
N = 125
7QC Tools
Q7T/PPT- 122
CASE STUDY
STEP 2 DETERMINE THRE LARGEST AND SMALLEST VALUEMinimum Maximum
9.9 9.3 10.2 9.4 10.1 9.6 10.1 9.9 9.8 9.3 10.29.8 9.8 10.1 9.9 9.7 9.8 10.0 9.9 9.6 9.6 10.19.7 9.4 9.6 10.0 9.8 9.9 10.4 10.1 10.0 9.4 10.410.2 10.1 9.8 10.1 10.3 10.0 9.8 10.2 10.7 9.8 10.79.9 10.7 9.3 10.3 9.9 9.8 9.5 9.8 9.4 9.3 10.79.3 10.2 9.2 9.9 9.7 9.9 9.5 9.8 9.4 9.2 10.29.0 9.5 9.7 9.7 9.8 9.8 9.6 9.3 9.7 9.0 9.810.0 9.7 9.4 9.8 9.4 9.6 10.3 10.0 9.8 9.4 10.39.5 9.7 10.6 9.5 10.1 10.0 10.1 9.8 9.3 9.5 10.69.6 9.4 10.1 9.5 10.1 10.2 9.5 9.8 9.3 9.3 10.210.3 9.6 9.7 9.7 10.1 9.8 10.0 9.7 10.0 9.6 10.39.5 9.5 9.8 9.9 9.2 10.0 9.7 10.0 9.7 9.2 10.09.9 10.4 9.3 9.6 10.2 9.7 9.7 9.7 10.7 9.3 10.79.9 10.2 9.8 9.3 9.6 9.5 10.7 9.6 9.3 10.7
9.0 10.7
N = 125
7QC Tools
Q7T/PPT- 123
CASE STUDY
STEP 4 Divide the ‘R’ in to No. Of Classes, referred to as ‘K’ 125 data points would be broken down in to 7 – 12 classes.
Method - 1
No.of data points No. of classes
Under 50 5 – 7
50 – 100 6 – 10
100 – 250 7 – 12
Over 250 10 - 20
Method – 2No. Of Classes – K =√N where,
N = No. Of sample
For example, if N = 125K =√125 = 11
Let us use K = 10 classes
7QC Tools
Q7T/PPT- 124
CASE STUDY
STEP 3 Obtain the range of R
Maximum value – Minimum Value = R
10.7 – 9.0 = 1.7
R = 1.7
7QC Tools
Q7T/PPT- 125
CASE STUDY
STEP 5 Determine the class width ‘H’
R (Range)= H
K (# of classes)1.7
= 0.1710
Can be rounded off to 0.20
7QC Tools
Q7T/PPT- 126
CASE STUDY
STEP 6 Divide the value of class boundaryFor simple determination of class boundaries, take the smallest individual measurement in the data set. Use this number or round to the next appropriate lowest number. This will be lower end point for our first class boundary.
In our example this would be 9.0. Now take this number and add the class width to it, 9.00 + 0.20.
But it is essential to fix class boundaries in such way that every observed reading will fit in to ‘one’ and ‘only’ class. Therefore, we may choose the class boundaries with one decimal place more than the observed readings.
For example, if the observations are in one decimal, the class boundaries will be in two decimals and so on.
For our case study, it will be 8.95 + 0.20 = 9.15
Finally, consecutively add the class width, to the lowest class boundary until the correct number of classes, approximately 10 and containing the range of all our numbers is obtained.
7QC Tools
Q7T/PPT- 127
CASE STUDY
STEP 7 Construct a frequency table
Class #
Class Boundaries Midpoint Frequency Total
1 8.95-9.15 9.05 1
2 9.15-9.35 9.25 9
3 9.35-9.55 9.45 16
4 9.55-9.75 9.65 27
5 9.75-9.95 9.85 29
6 9.95-10.5 10.05 26
7 10.5-10.35 10.25 11
8 10.35-10.55 10.45 1
9 10.55-10.75 10.65 5
10 10.75-10.95 10.85 0
7QC Tools
Q7T/PPT- 128
CASE STUDY
STEP 8 Construct Histogram
05
101520253035
8.95 9.15 9.35 9.55 9.75 9.95 10.15 10.35 10.55 10.75Thickness in mm
Freq
uenc
y USL
The specification for the thickness characteristic is 7.5 to 10.5, with a target of 9. The above Histogram indicates the process is targeted high and that 3% may be above the upper specification limit.
7QC Tools
Q7T/PPT- 129
HISTOGRAM
Having two peaks
Having a cut end
Having extraordinarily high value in
the end internal
Having an isolated peak
Right & Left symmetrical
Slopping the right
Slopping to the left
7QC Tools
Q7T/PPT- 130
Average response time to patient rings (1st shift)
050
100150200
1 2 3 4 5 6 7 8 9 1Minutes
# O
f Res
pons
es
Histogram - Daily Example Height of 100 men
010203040
63 65 67 69 71Height (inches)
# O
f Men
Histogram-ManufacturingPrint Density
02468
0.6 0.8 0.1 1.2 1.4Block density of print
Freq
uenc
y
Histogram – Administration/Service Example
7QC Tools
Q7T/PPT- 131
To analyze processes and discover items to be improved
To research process capability
To control the process (in a time series)
To verify effects of an improvement
Histogram
Application
7QC Tools
Q7T/PPT- 132
A Histogram can be used:• To display large amounts of data values in a relatively
simple chart form.• To tell relative frequency of occurrence.• To easily see the distribution of the data.• To see if there is variation in the data.• To make future predictions based on the data.
Histogram
Uses of Histogram
7QC Tools
Q7T/PPT- 133
Scatter diagramScatter diagram
Scatter diagram
7QC Tools
Q7T/PPT- 134
In actual practice, it is often essential to study the relation of two corresponding data types
For example, to what extent will the dimension of a machined part be varied by the change in the speed of a lathe?
Scatter diagram Scatter diagram
7QC Tools
Q7T/PPT- 135
To study the relation of two variables such as the speed of the lathe & the dimension of the part we can use what is called a Scatter diagram.
Scatter diagram
7QC Tools
Q7T/PPT- 136
The two variables we will deal with are:
a) A quality – characteristic & a factor affecting it,
b) Two related quality characteristics, or
c) Two factors relating to a single quality characteristic.
Let’s consider the steps in making a scatter diagram
Scatter diagram
7QC Tools
Q7T/PPT- 137
Examples of such relationships
Speed Vs Mileage
Cutting speed Vs Tool life
Etc……
Scatter diagram
7QC Tools
Q7T/PPT- 138
Step 1
Collect paired data (x,y) between which you want to study the relations & arrange the data in a table. It is desirable to have at least 30 pairs of data.
Scatter diagram
7QC Tools
Q7T/PPT- 139
Step 2
Find the maximum & minimum values for both x & y. Decide the scales of horizontal & vertical axes so that both the lengths become approximately equal, then the diagram will be easier to read. Keep the number of unit graduations between 3 to 10 for each axis & use round numbers to make it easier to read.
=
Scatter diagram
Choosing units that express the range of the x and y values, draw an x scale along the horizontal axis and a y scale along the vertical axis.
7QC Tools
Q7T/PPT- 140
Step 3Plot the data on the section paper. Step 4Enter all necessary items. Make sure that the following
items are included so that anyone besides the maker of the diagram can understand at a glance:
a) Title of the diagramb) Time intervalc) Number of pairs of datad) Title & units of each axise) Name (etc) of the person who made the diagram
Scatter diagram
7QC Tools
Q7T/PPT- 141
Example
A manufacturer of plastic tanks who made them using the blow moulding process encountered problems with defective tanks that had thin tank walls. It was suspected that the variation in air pressure, which varied from day to day, was the cause of the defective thin walls. The table shows data on blowing pressure & percent defective. Let us draw a scatter diagram using this data according to the steps given previously.
Scatter diagram
7QC Tools
Q7T/PPT- 142
Date Air pressure Percent(kgf/cm2) Defective
Oct-01 8.6 0.8892 8.9 0.8843 8.8 0.8744 8.8 0.8915 8.4 0.8746 8.7 0.8867 9.2 0.9118 8.6 0.9129 9.2 0.89510 8.7 0.89611 8.4 0.89412 8.2 0.86413 9.2 0.92214 8.7 0.90915 9.4 0.90516 8.7 0.89217 8.5 0.87718 9.2 0.88519 8.5 0.86620 8.3 0.89621 8.7 0.89622 9.3 0.92823 8.9 0.88624 8.9 0.90825 8.3 0.88126 8.7 0.88227 8.9 0.90428 8.7 0.91229 9.1 0.92530 8.7 0.872
Data of blowing air pressure & percent defective of plastic tank
Scatter diagram
7QC Tools
Q7T/PPT- 143
Step 1
As seen in the table, we have 30 pairs of data.
Step 2
In this example, let blowing air pressure be indicated by X(horizontal axis), & percent defective by Y (vertical axis).
Then,
The maximum value of X: Xmax = 9.4 (kgf/cm2)
The minimum value of X : Xmin = 8.2 (kgf/cm2)
The maximum value of Y: Ymax = 0.928 (%)
The minimum value of Y : Ymin = 0.864 (%)
Scatter diagram
7QC Tools
Q7T/PPT- 144
We mark off
the horizontal axis in 0.5(kgf/cm2) intervals, from 8.0 to 9.5 (kgf/cm2) and
the vertical axis in0.01(%) intervals, from 0.85 to 0.93(%)
Step 3
Plot the data.
Scatter diagram
7QC Tools
Q7T/PPT- 145
0.85
0.86
0.87
0.88
0.89
0.9
0.91
0.92
0.93
8 8.5 9 9.5
Scatter diagram
7QC Tools
Q7T/PPT- 146
Step 4
Enter the time interval of the sample obtained (oct.1 – oct 30) number of samples (n = 30), horizontal axis (blowing air pressure [kgf/cm2]), vertical axis (percent defective [%]), and title of diagram (scatter diagram of blowing air pressure & percent defective).
0.85
0.86
0.87
0.88
0.89
0.9
0.91
0.92
0.93
8 8.5 9 9.5
(Oct 1 – Oct 30)
n=30
P er c
e nta
ge d
e fe c
ti ve
Blowing air pressure
Scatter diagram
7QC Tools
Q7T/PPT- 147
How to read scatter diagrams ?You can grasp the correlation between pairs of data just by looking at the shape of a scatter diagram. 5 examples are given below
Scatter diagram
7QC Tools
Q7T/PPT- 148
05
101520253035
0 5 10 15 20
Series1
Positive correlation
Scatter diagram
If y increases with x or the vice versa,then x and y are positively correlated.
7QC Tools
Q7T/PPT- 149
050
100150200250300350
0 100 200 300 400
Series1
Negative correlation
Scatter diagram
If y decreases as x increases, then the two
types of data are negatively correlated.
7QC Tools
Q7T/PPT- 150
0100200300400500600700
0 100 200 300 400
Series1
No correlation
Scatter diagram
If no significant relationship is apparent between x and y, then the two data types are not correlated.
7QC Tools
Q7T/PPT- 151
0
10
20
30
40
0 5 10 15 20
Series1
0
100
200
300
400
500
0 100 200 300 400
Series1
Positive correlation may be present Negative correlation may be present
Scatter diagram
7QC Tools
Q7T/PPT- 152
Let us do an exercise !
Let us say you are simply not satisfied with the marks that your younger brother/sister is scoring. So you want him/her to study more. But does studying more really help? How to find out?
Scatter diagram
7QC Tools
Q7T/PPT- 153
Try a scatter diagram !
No. of hours of study/day0.5 1.0 1.5 2.0 2.5
Perc
enta
ge o
f mar
ks50
60
70
80
90
Scatter diagram
7QC Tools
Q7T/PPT- 154