September 2008 Edition
managing for tomorrow
Seven quality tools can help supervisors roll a winner
By Elizabeth Maze-Emery
Think
of dice … consider the probability of rolling a 7. You have six
possible combinations: 1 and 6, 2 and 5, 3 and 4, 4 and 3, 5 and 2,
6 and 1. So the probability is 6/36, or 16.7 percent, that you will
roll a 7.
In manufacturing, if this is the percentage produced within
specification, you’ll be in trouble fast — which is why it’s a good
thing there are Seven Quality Tools to help us.
When we think of rolling dice or playing cards, we think of
chance playing a key role in the outcome.
But being able to predict the likelihood of future events is not
always enough in manufacturing. A wise man once said that in order
to control the future, we must master the lessons of the past.
Through the use of probability statistics, and by knowing something
about recent past, we can predict and respond
to control the likelihood of future events.
The discipline of total quality control uses Seven Quality Tools
to identify focus for continuous improvement efforts in
manufacturing. Over the years, quality experts realized that many
quality-related problems could be solved with these tools.
1) Check Sheet
Think of a check sheet as similar
to a grocery list. A check sheet is a list of all necessary key settings, tools,
or raw materials are needed to make the product. A check sheet can also be used
to capture pertinent data.
2) Cause & Effect Diagram
A man by the name of
Kaoru Ishikawa developed a diagram that is commonly referred to as a cause and
effect fishbone diagram. Much like when our normally dependable car stops
working, if our manufacturing process exhibits a problem, we need to ask
questions to determine what causes contribute to the effect.
By assessing possible causes related to the 5Ms — materials,
machines, measurements, man, and methods — we can seek effect
relationships to understand today’s problem.
3) Pareto chart
The Pareto chart was named
for Vilfredo Pareto, whose principles allow us to identify the few truly
important cause factors.
In a Pareto chart, the reasons are plotted with the greatest
reason first and in descending order of importance. At a glance, the
greatest contributing reasons are apparent.
4) Flowchart
The intent of a flowchart is to
describe the various steps and decisions in a process. Consider a chart of
getting in our car: step one, open door; step two, get in; step three, insert
and turn key; step four, "Did the car start?" Depending on this answer, there
are other steps outlined graphically.
5) Histogram
Consider a checksheet that
records temperature readings. Consider that we make a tick mark for each
reading within a five-degree temperature category.
For the histogram, we plot the data as adjacent bars with categories across
the bottom X axis and the frequency of readings on the vertical Y axis. The
result is the histogram showing data proportions.
6) Control Chart
A control chart helps the control of the process based upon knowing something
about the normal in-specification manufacturing process. The process average or
in-specification mean is plotted as the centerline. Additionally upper and lower
control limits can be calculated and plotted.
Think of this process average as the centerline of the road and the control
limits are the edges of the road that we must stay between. By plotting all new
data within these limits, we can monitor and respond to trends or out-of-control
conditions.
7) Scatter diagram
The scatter diagram has the ability to show nonlinear relationships between
variables by plotting variables against each other. Variables with no
relationships will result in scattered data plots. A plotting of variables that
have relationships will show clear correlations.
If your intent is to master dice in the game of craps, consult the applied
mathematics of game theory. If your intent is to master manufacturing processes,
consult more information on the Seven Quality Tools to ensure process total
quality control.
Elizabeth Maze-Emery is a quality professional from Dayton, OH. For
information about these quality tools, related topics, or an extended version of
this article that includes sample charts, e-mail her at
emazeemery@jiu.edu.
What do you think?
Will the information in this article increase efficiency or
save time, money, or effort? Let us know by e-mail from our website at
www.ToolingandProduction.com or e-mail the editor at
dseeds@nelsonpub.com.
editor's blogs
Off the Toolpath
EASTEC marks 30th show with spotlight on medical devices
The recession hasn’t stopped business, if the activity at the EASTEC Advanced Productivity Exposition is to judge. The show, in its 30th year, drew 570 exhibitors, down from 608 in 2008 and 650 in 2007. About 15,000 attendees pre-registered. Last year’s show tallied 14,000 attendees. The largest industrial tool trade show on the East Coast, EASTEC was held May19-21 in West Springfield, MA.
by Dennis Seeds, Editor-in-Chief
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