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Copy of The Seven Quality Control Tools and
Transcript of Copy of The Seven Quality Control Tools and
Tool 7: Control Chart
By: Bassel and Hang
Tool 1: The Pareto Chart
Also called: Pareto diagram, Pareto analysis.
A Pareto chart is a bar graph. The lengths of the bars represent frequency or cost (time or money), and are arranged with longest bars on the left and the shortest to the right. In this way the chart visually depicts which situations are more significant.
Tool 2: Cause and Effect Diagram
Also Called: Cause–and–Effect Diagram, Ishikawa Diagram
Variations: cause enumeration diagram, process fishbone, time–delay fishbone, CEDAC (cause–and–effect diagram with the addition of cards), desired–result fishbone, reverse fishbone diagram
The fishbone diagram identifies many possible causes for an effect or problem. It can be used to structure a brainstorming session. It immediately sorts ideas into useful categories
Tool 3: Check Sheet
Also called: defect concentration diagram
A check sheet is a structured, prepared form for collecting and analyzing data. This is a generic tool that can be adapted for a wide variety of purposes.
Tool 4: Histogram
A frequency distribution shows how often each different value in a set of data occurs. A histogram is the most commonly used graph to show frequency distributions. It looks very much like a bar chart, but there are important differences between them.
Tool 6: Control Chart
Also called: statistical process control
The control chart is a graph used to study how a process changes over time. Data are plotted in time order. A control chart always has a central line for the average, an upper line for the upper control limit and a lower line for the lower control limit. These lines are determined from historical data. By comparing current data to these lines, you can draw conclusions about whether the process variation is consistent (in control) or is unpredictable (out of control, affected by special causes of variation).
Control charts for variable data are used in pairs. The top chart monitors the average, or the centering of the distribution of data from the process. The bottom chart monitors the range, or the width of the distribution. If your data were shots in target practice, the average is where the shots are clustering, and the range is how tightly they are clustered. Control charts for attribute data are used singly.
The objective of process control is thus to produce the deliverables meeting the specifications by closely monitoring the processes.
The process control should be planned. The intermediate checks or examination or measurements should be planned.
When analyzing data about the frequency of problems or causes in a process.
When there are many problems or causes and you want to focus on the most significant.
When analyzing broad causes by looking at their specific components.
When communicating with others about your data.
When to Use a Fishbone Diagram
When data can be observed and collected repeatedly by the same person or at the same location.
When collecting data on the frequency or patterns of events, problems, defects, defect location, defect causes, etc.
When collecting data from a production process
• When the data are numerical.
• When you want to see the shape of the data’s distribution, especially when determining whether the output of a process is distributed approximately normally.
• When analyzing whether a process can meet the customer’s requirements.
• When analyzing what the output from a supplier’s process looks like.
• When seeing whether a process change has occurred from one time period to another.
• When determining whether the outputs of two or more processes are different.
• When you wish to communicate the distribution of data quickly and easily to others.
Stratification is a technique used in combination with other data analysis tools. When data from a variety of sources or categories have been lumped together, the meaning of the data can be impossible to see. This technique separates the data so that patterns can be seen.
Pareto Chart Examples
Example #1 shows how many Student complaints were received in each of five categories.
Example #2 takes the largest category, “Halls,” from Example #1, breaks it down into six categories of Halls-related complaints, and shows cumulative values.
If all complaints cause equal distress to the customer, working on eliminating document-related complaints would have the most impact, and of those, working on quality certificates should be most fruitful.
Fishbone Diagram Example
For example, under the heading “Machines,” the idea “materials of construction” shows four kinds of equipment and then several specific machine numbers.
Note that some ideas appear in two different places. “Calibration” shows up under “Methods” as a factor in the analytical procedure, and also under “Measurement” as a cause of lab error. “Iron tools” can be considered a “Methods” problem when taking samples or a “Manpower” problem with maintenance personnel.
When to Use a Pareto Chart?
• When identifying possible causes for a problem.
• Especially when a team’s thinking tends to fall into ruts.
When to Use a Check Sheet
Check Sheet Example
The figure below shows a check sheet used to collect data on telephone interruptions. The tick marks were added as data was collected over several weeks.
When to Use a Histogram?
Tool 5: Scatter Diagram
Also called: scatter plot, X–Y graph
The scatter diagram graphs pairs of numerical data, with one variable on each axis, to look for a relationship between them. If the variables are correlated, the points will fall along a line or curve. The better the correlation, the tighter the points will hug the line.
• When you have paired numerical data.
• When your dependent variable may have multiple values for each value of your independent variable.
• When trying to determine whether the two variables are related, such as…
o When trying to identify potential root causes of problems.
o After brainstorming causes and effects using a fishbone diagram, to determine objectively whether a particular cause and effect are related.
o When determining whether two effects that appear to be related both occur with the same cause.
o When testing for autocorrelation before constructing a control chart.
When to Use a Scatter Diagram??
Steps Involved in Pareto Diagram
Calculate the share of each cause as a percentage of total.
Then arrange the causes in descending order.
If there are too many small causes contributing too little to the total, group them as miscellaneous.
Draw column graphs for each cause equal to their contribution
what is Quality Control?
Benefits of Quality
Intro 7 QC Tools
"Quality control consists of developing, designing, producing, marketing, and servicing products and services with optimum cost-effectiveness and usefulness, which customers will purchase with satisfaction."
Dr. Kaoru Ishikawa
What is Quality Control?
Benefits of Quality Control...
Introducing the 7 QC Tools
Dr. Walter Shewhart & Dr. W Edward Deming
Introduce Quality Control to Japan
Pareto Chart & Diagram
Scatter Diagram Example
When to Use a Control Chart
• When controlling ongoing processes by finding and correcting problems as they occur.
• When predicting the expected range of outcomes from a process.
• When determining whether a process is stable (in statistical control).
• When analyzing patterns of process variation from special causes (non-routine events) or common causes (built into the process).
• When determining whether your quality improvement project should aim to prevent specific problems or to make fundamental changes to the process.
Control Chart Example
Tool 7: Stratification
When to Use Stratification
• Before collecting data.
• When data come from several sources or conditions, such as shifts, days of the
week, suppliers or population groups.
• When data analysis may require separating different sources or conditions.
R. Tague’s The Quality Toolbox, Second Edition, ASQ Quality Press, 2004, pages 376-378
Nancy R. Tague’s The Quality Toolbox, Second Edition, ASQ Quality Press, 2004, pages 247–249.
Excerpted from Nancy R. Tague’s The Quality Toolbox, Second Edition, ASQ Quality Press, 2004, pages 292–299.
Nancy R. Tague’s The Quality Toolbox, Second Edition, ASQ Quality Press, 2004, pages 141–142.
Typical Histogram Shapes and What They Mean
Has or has not
Good or bad
Pass or fail
Accept or reject
Conforming or nonconforming
Measured values (dimension, weight, voltage, surface, etc.)
Data on Read Beads in Samples
A = points in upper left + points in lower right
B = points in upper right + points in lower left
Q = the smaller of A and B
N = A + B
Some Other Tools Introduced
The Flow Diagrams
Design of experiments (DOX)
The Flow Diagram
Halls Parking Library Mail Others