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7/30/2019 QM - Six Sigma
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Chapter 20 Six Sigma
Management
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Six Sigma (a registered trademark of the Motorola
Corp.) is the relentless and rigorous pursuit of the
reduction of variation in all critical processes to achievecontinuous and breakthrough improvements that impact
the bottom line of the organization and increase customer
satisfaction.
It is an organizational initiative designed to createmanufacturing, service and administrative processes that
produce approximately 3.4 defects per million.
Opportunities (DPMO).
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Relationship between the Voice of the Customer
and the Voice of the Process
Six Sigma management promotes the idea that the
distribution of output for a process (the Voice of the Process)
should take up no more than half of the tolerance allowed by
the specification limits (the Voice of the Customer)
This assumes that the measurement data is from a stable and
normal distribution of output whose mean can shift by as
much as 1.5 standard deviations over time.
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The following figure shows the Voice of the Customer asspoken in the language of a nominal value, m, and the
lower and upper specification limits, LSL and USL, for aquality characteristic.
This assumes
Distribution of process output is measurement data
The process is stable
The distribution is normal The process average is on nominal
The distance between nominal and either specification limit is 3times the process standard deviation
If these five conditions are met we all the process a 3-
sigma process.
A 3-sigma process will produce 2,700 defects per millionopportunities.
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LSL USL
3-sigma Process
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An Example of a 3-sigma Process
The number of days to complete a month accountingreport is stable and normally distributed with an average
of 7 days and a standard deviation of 1 day.
The lower specification limit is 4 days and the upper
specification limits is 10 days.
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Next we see a quality characteristic represented by
measurement data that:
Is stable Is normally distributed
Has a process output that can shift by as much as 1.5 standard
deviations on either side of nominal
Has a distance between nominal and either specification limit of 3
standard deviations of process output.
This is a 3-sigma process with a 1.5 sigma shift in the
mean.
This process will generate 66,811 defects per million
opportunities or 93.33189% of its output between thespecification limits.
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Accounting process with process average shifts of 1.5
standard deviations.
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Next we see a scenario where the voice of the process
takes up only half the distance between the specification
limits. The process mean remains the same, but theprocess standard deviation has been reduced to one half-
day
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Output for the monthly accounting process with the
standard deviation reduced to one-half day through
process improvement activities.
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Next we will see the voice of the customer and the voice
of the process for a quality characteristic that:
Is represented by measurement data
Is stable
Is normally distributed
Has a process average that can shift by as much as 1.5 standard
deviations on either side of nominal Has the distance between nominal and either specification limit is
6 standard deviations of the process output.
This is a process that will generate 3.4 defects per million
opportunities, or 99.99966% of its output within
specification limits in the near future.
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Six sigma accounting process with a 1.5 sigma shift in
the mean