Ishikawa’s Basic Tools of Quality
• Kaoru Ishikawa developed seven basic
visual tools of quality so that the average
person could analyze and interpret data.
COURSE: Quality management methods
Basic Tools of Quality
4. lecture
• These tools have been used worldwide by
companies, managers of all levels and
employees.
Seven Quality Control Tools
1.
2.
3.
4.
• Remember the 80/20 rule states that approximately 80% of
the problems are created by approximately 20% of the
causes.
5. Scatter Diagram
6. SPC Chart
7. Cause-and-Effect
Diagram
(64)
Pareto Chart
Flow Chart
Start/
Finish
40
Operation
Operation
Decision
Operation
Operation
Operation
Decision
Start/
Finish
30
20
(13)
10
(10)
(6)
(3)
(2)
(2)
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Causes of poor quality
CAUSE
NUMBER OF
DEFECTS
Poor design
Wrong part dimensions
Defective parts
Incorrect machine calibration
Operator errors
Defective material
Surface abrasions
PERCENTAGE
80
16
12
7
4
3
3
64 %
13
10
6
3
2
2
125
100 %
Check Sheet
50
W
ro
ng
Percent from each cause
60
Pareto Analysis
– Pareto charts are used to identify and prioritize
problems to be solved.
– They are actually histograms aided by the 80/20 rule
adapted by Joseph Juran.
Pareto Analysis
Flow Chart
Check Sheet
Histogram
70
Pareto Charts
• Pareto Chart Defined
Histogram
Histogram
Histogram
• Used to visualize the distribution
Histogram of univariate sample - bimodal tendency
0.04
20
Histogram of univariate sample
0.08
0.03
15
10
Density
0.06
Density
histogram is a
graphical
representation
showing a visual
impression of
the distribution
of data.
0.04
0.01
0.02
5
0.00
0.00
20
0
30
40
50
20
40
60
80
measurement scale
1 2
measurement scale
6 13 10 16 19 17 12 16 2017 13 5 6 2 1
Histogram
Scatter Diagram
Histograms
Histogram of univariate sample - skewed tendency
• Histogram Defined
Y
– A histogram is a bar graph that shows
frequency data.
– Histograms provide the easiest way to
evaluate the distribution of data.
0.04
0.03
Density
0.02
0.02
0.01
0.00
0
20
40
60
80
measurement scale
X
Scatter Diagrams
• Scatter Diagrams Defined
– Scatter Diagrams are used to study and
identify the possible relationship between the
changes observed in two different sets of
variables.
Scatter Diagrams
• An Example of When a Scatter Diagram
Can Be Used
– A scatter diagram can be used to identify the
relationship between the production speed of
an operation and the number of defective
parts made.
Scatter Diagrams
• An Example of When a Scatter Diagram Can Be Used
(cont.)
– Displaying the direction of the relationship will determine whether
increasing the assembly line speed will increase or decrease the
number of defective parts made. Also, the strength of the
relationship between the assembly line speed and the number of
defective parts produced is determined.
Control Chart
Control Charts
24
UCL = 23.35
Number of defects
21
c = 12.67
18
• Control Charts Defined
15
– Control charts are used to determine whether
a process will produce a product or service
with consistent measurable properties.
12
9
Cause-and-Effect Analysis
6
LCL = 1.99
3
2
4
6
8
10
12
14
16
Sample number
Cause and Effect Diagram
• Cause and Effect Diagram Defined
– The cause and effect diagram is also called the Ishikawa
diagram or the fishbone diagram.
– It is a tool for discovering all the possible causes for a particular
effect.
– The major purpose of this diagram is to act as a first step in
problem solving by creating a list of possible causes.
Cause & Effect Diagrams
• Bones should not include solutions
• Bones should not include lists of process
steps
• Bones include the possible causes
The '5-Why' Method
• The 5 Whys is a question-asking
technique used to explore the cause-andeffect relationships underlying a particular
problem. The primary goal of the
technique is to determine the root cause of
a defect or problem.
• The method involves asking "Why … ?"
five times in succession.
Tree diagram
Short history of the method
• The technique was originally developed by Sakichi
Toyoda and was used within the Toyota Motor
Corporation during the evolution of its manufacturing
methodologies. It is a critical component of problemsolving training, delivered as part of the induction into the
Toyota Production System.
• The architect of the Toyota Production System, Taiichi
Ohno, described the 5 Whys method as "the basis of
Toyota's scientific approach . . . by repeating why five
times, the nature of the problem as well as its solution
becomes clear.
• The tool has seen widespread use beyond Toyota, and
is now used within Kaizen, lean manufacturing, and Six
Sigma.
Example
The vehicle will not start. (the problem).
1. Why? - The battery is dead. (first why)
2. Why? - The alternator is not functioning. (second why)
3. Why? - The alternator belt has broken. (third why)
4. Why? - The alternator belt was well beyond its useful service life
and not replaced. (fourth why)
5. Why? - The vehicle was not maintained according to the
recommended service schedule. (fifth why, a root cause)
6. Why? - Replacement parts are not available because of the extreme
age of the vehicle. (sixth why, optional footnote)
Start maintaining the vehicle according to the recommended service
schedule. (possible 5th Why solution)
Purchase a different vehicle that is maintainable. (possible 6th Why
solution)