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Fine Tune Your Production Process to Achieve Six Sigma using Design
of Experiments
Many manufacturing processes and some service processes can benefit from
using Design of Experiments (DOE) to optimize their results. Without
DOE, you're stuck with the world's slowest method for success-trial
and error. With Design of Experiments, you just have to test at
the high (+) and low (-) values for any particular "design factor"
(e.g., pressure, temperature, time, etc.) from your QFD House of Quality,
not every increment in between. And you can test more than one factor
at a time.
You can make Design of Experiments wildly complex or straightforward
and simple. In my first Design of Experiments class we spent an
inordinate amount of time understanding "orthogonal arrays"
and all of the other "behind the scenes" mathematics, but you
don't need to know all of that to conduct a Design of Experiments study.
Manufacturing Example
For simplicity, let's assume you are writing a cookbook and want to find
the best directions for baking a cake (which is similar to baking paint
on a car finish). To do this, you will want to establish the high-low
settings for each "factor" in your study. Let's suppose you
have four factors (a four factor experiment):
- Pan shape: Round (low) vs square (high) pan
- Ingredients: 2 vs 3 cups of flour
- Oven temperature: 325 vs 375 degrees
- Cooking Time: 30 vs 45 minutes
Let's say that you'll rank each resulting cake on a 1-10 scale for overall
quality.
You then use the +/- values in the orthogonal array to guide your test
of every combination (16 total):
- High: all high values (+ + + + = square pan, 3 cups, 375 degrees,
45 minutes)
- Low: all low values (- - - - = round pan, 2 cups, 325 degrees,
30 minutes)
- In Between: every other combination ("+ + + -", "+
+ - -", and so on).
To optimize your results, you might want to run more than one test of
each combination. Then you just plug your data into a 16-factor DOE
template (Taguchi or Plackett-Burman format) like the in the QI Macros
and observe the interactions.
Here is a sample QI Macros Plackett Burman DOE Template
The QI Macros for Excel SPC Software
includes Taguchi 4, 8 and 16 factors and Plackett-Burman. You can buy
a DOE template separately or as part of the QI Macros.
Order Design of Experiments Template
Design of Experiments - $99 Download Only
Order the QI Macros for Excel SPC Software
QI Macros Excel SPC Software for Histograms and Control Charts $139 Plus S&H
In Design of Experiments, they talk about "confounding"
which simply means that one factor affects another. You'd expect
a higher temperature to result in a shorter cooking time, and vice versa,
but does a square pan take longer than a round one? Using the results,
a Design of Experiments program will draw the interactions between
each of the factors as a line graph.
If the two lines are parallel, there's no interaction. Is one end higher
than the other? If so, you can immediately tell which value (high/low)
gives you the best result.
If the two lines cross, there is an interaction (confounding). And, by
looking at where the two lines intersect on the graph, you can determine
the optimum settings (e.g., time and temperature) to get the best cake.
To do this using trial-and-error would take hundreds, maybe even thousands
of trials, not just 16.
Here are sample charts created by the QI Macros.
Service Example:
People who send direct mail rigorously tally their results from each mailing.
They will test one headline against another headline, one sales proposition
against another, or one list of prospects against another list, but they
usually only do one test at a time. What if you can't wait? Using Design
of Experiments, you could test all of these factors simultaneously.
Design your experiment as follows:
- Headline: Headline #1 (high), Headline #2 (low)
- Sales proposition: Benefit #1 (high), Benefit #2 (low)
- List: List #1 (high), List #2 (low)
- Guarantee: Unconditional (high), 90 days (low)
This way you might find that headline #1 works best for list #2 and vice
versa. You might find that one headline works best with one benefit.
Design of Experiments can help you shorten the time and effort
required to discover the optimal conditions to produce Six Sigma quality
in your delivered product or service. Don't let the +/- arrays
baffle you. Just pick 2, 3, or 4 factors, pick sensible high/low
values, and design a set of experiments to determine which factors
and settings give the best results.
Start with a 2-factor and work your way up. Have fun! It's just not that
hard, especially with the right software.
Design of Experiments DOE Excel Template includes Taguchi 4,8
and 16 factors and Placket-Burman. Buy one separately or as part of the
QI Macros for Excel SPC Software.
Order Design of Experiments Template
Design of Experiments - $99 Download Only
Order the QI Macros for Excel SPC Software
QI Macros Excel SPC Software for Histograms and Control Charts $139 Plus S&H
© 2007 KnowWare International Inc. (888) 468-1537
knowwareman@qimacros.com
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This is one of 19 SPC charts and over 70 templates included with the QI Macros
for Excel SPC Software $139. Just select the data you want graphed and in just
seconds the QI Macros will draw the graph and do all the math for you.
The QI Macros draws line, pie, bar, pareto, box whisker, histogram (Cp, Cpk),
scatter and control charts (with stability analysis).
Templates include the Ishikawa diagram, QFD, DOE, FMEA, PPAP, and Gage R&R
for MSA. Performs ANOVA, t-test, F-test, and regression analysis.
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