Chapter 2 Basic Tools for Improving Quality

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# Chapter 2 Basic Tools for Improving Quality - PowerPoint PPT Presentation

Chapter 2 Basic Tools for Improving Quality. 7 Basic Tools by Ishikawa. Histogram Pareto chart Scatter plot Control chart Cheek sheet Cause-and-effect diagram Defect concentration diagram. 2.1 Histogram.

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### Chapter 2Basic Tools for Improving Quality

7 Basic Tools by Ishikawa
• Histogram
• Pareto chart
• Scatter plot
• Control chart
• Cheek sheet
• Cause-and-effect diagram
• Defect concentration diagram
2.1 Histogram
• A histogram is a bar chart that shows the relative frequencies of observations in each of several classes.
• Rule for determining the number of classes:
• “Power of 2 rule”: for n observations, we would use a classes, where 2a-1 < n < 2a
• Roundup a = lnn / ln 2 (=ROUNDUP(LN(100)/LN(2), 0)
• a ~
2.2 Pareto Charts
• A Pareto chart is a bar graph that shows the relative frequencies of observations in a descending order.
• draws its name from an Italian economist, VilfredoPareto (1848–1923)
• J. M. Juran is credited with being the ﬁrst person to apply it to industrial problems
2.3 Scatter Plots
• A scatter plot is another simple graphical device
• The simplest type is a bivariate scatter plot, in which two quantities are plotted.
• Scaling of the two axes is somewhat arbitrary
• A time sequence plot is a type of scatter plot in that data on one variable are plotted against a second variable, time.
• A probability plot is another type of scatter plot.
Variations of Scatter Plots
• Use number or special symbols for duplicated data points.
• Use “range frames”, instead of scales
2.4 Control Charts
• A control chart is a time sequence plot with “decision lines” added.
• These decision lines are used to try to determine whether or not a process is in control.
• Type I and II errors
10

9

1

2

3

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5

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7

8

Typical Control Chart

Upper

control

limit

2s

1s

Central

Line

95%

99.73%

1s

Lower

control

limit

-1

-3

-2

=0

1

2

3

2s

Sample number

2.5 Check Sheet
• A check sheet is a means of recording historical data on causes of nonconformities or nonconforming units.
• The general idea is to record all pertinent information relative to nonconformities and nonconforming units, so that the sheets can facilitate process improvement.
• Such information might include notes on raw materials, machine performance, or operator changes.
2.6 Cause-and-Effect Diagram
• The cause-and-effect diagram was introduced in Japan in 1943 by Professor Kaoru Ishikawa of the University of Tokyo.
• For that reason it is sometimes called an Ishikawa diagram; it has also been called a ﬁshbone chart.
2.7 Defect Concentration Diagram
• It is simply a schematic diagram that shows the various sides of a unit of production, with the positions where nonconformities occur pinpointed.
• Afﬁnity Diagram
• Interrelationship Digraph
• Tree Diagram
• Prioritization Matrix
• Matrix Diagram
• Process Decision Program Chart
• Activity Network Diagram
2.8.1 Afﬁnity Diagram
• An afﬁnity diagram is a set of ideas about a particular topic that are grouped into clusters.
• The diagram is the end product of brainstorming that is performed in a prescribed manner.
2.8.2 Interrelationship Digraph
• An interrelationship digraph is used for identifying and exploring causal relationships between related ideas.
• This is a step beyond an afﬁnity diagram, as an interrelationship digraph is a ﬁgure with arrows indicating relationships between ideas.
2.8.3 Tree Diagram
• A tree diagram is somewhat similar to a cause-and-effect diagram in that a desired effect (e.g., reducing delivery delays) can be shown pictorially as related to the factors that can lead to the effect.
• A tree diagram will generally more closely resemble a company organizational chart in appearance than a cause-and-effect diagram.
• A tree diagram is a more structured display than either an afﬁnity diagram or an interrelationship digraph.
2.8.4 Prioritization Matrix
• A prioritization matrix is a relative ranking of issues jobs, objectives, products, and so on.
• The ranking is accomplished by comparing the components pairwise so that a logical and consistent ranking results.
2.8.5 Matrix Diagram
• A matrix diagram is used for showing relationships between two or more sets of ideas, projects, and so on.
• The matrix can have one of several different forms.
• At least ﬁve forms have been used:
• C-shaped
• L-shaped
• T-shaped
• X-shaped, and
• Y-shaped
2.8.6 Process Decision Program Chart
• A process decision program chart is a listing of undesirable events and corresponding contingency actions relative to planned actions.
• It is used when there is considerable concern about the possibility of negative unanticipated outcomes.
2.8.7 Activity Network Diagram
• This is essentially a combination of two well-known techniques: PERT (Program Evaluation and Review) and CPM (Critical Path Method).