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6 Sigma Statistical Process Control (SPC) Software for Windows 95/98/NT/2000/XP/ME

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Six Sigma Successes
What Are The Six Steps To Six Sigma
What Is Six Sigma and the 1.5 Shift? The Concepts And Theories

Concepts of Six Sigma resource as initiated by Motorola in 1985

In order to understand six sigma, you must understand how Cpk compares to PPM.


Let?s get real here. Is it truly necessary to go for zero defects? Why isn?t 99.9% defect-free good enough? Here are some examples of what life would be like if 99.9% were "good enough:"

  • 1 HOUR OF UNSAFE DRINKING WATER EVERY MONTH
  • 2 LONG OR SHORT LANDINGS AT EVERY AMERICAN AIRPORTS EACH DAY
  • 400 LETTERS PER HOUR WHICH NEVER ARRIVE AT THEIR DESTINATION
  • 500 INCORRECT SURGICAL OPERATIONS EACH WEEK
  • 3,000 NEWBORNS ACCIDENTALLY FALLING FROM THE HANDS OF NURSES OR DOCTORS EACH YEAR
  • 4,000 INCORRECT DRUG PRESCRIPTIONS PER YEAR
  • 22,000 CHECKS DEDUCTED FROM THE WRONG BANK ACCOUNT EACH HOUR
  • 32,000 MISSED HEARTBEATS PER PERSON PER YEAR

Here are some examples of what life would be like at Six Sigma

  • 13 WRONG DRUG PRESCRIPTIONS PER YEAR
  • 10 NEWBORNS ACCIDENTALLY FALLING FROM THE HANDS OF NURSES OR DOCTORS EACH YEAR
  • 1 LOST ARTICLE OF MAIL PER HOUR

SUDDENLY, THE QUEST FOR SIX SIGMA ISN’T SO BAD

THE SIX STEPS TO SIX SIGMA USING

Step #1 – Identify the product you create or the service you provide

In other words … WHAT DO YOU DO?

Step #2 – Identify the Customer(s) for your product or service, and determine what they consider important i.e. Customer Requirements

In other words … WHO USES YOUR PRODUCT AND SERVICES?

Step #3 – Identify your needs (to provide product/service so that it satisfies the Customer)

In other words … WHAT DO YOU NEED TO DO YOUR WORK?

Step #4 – Define the process for doing your work

In other words … HOW DO YOU DO YOUR WORK?

Step #5 – Mistake-proof the process and eliminate wasted efforts using…

In other words … HOW CAN YOU DO YOUR WORK BETTER?

Step #6 – Ensure continuous improvement by measuring, analyzing and controlling the improved process using
DMAIC – (Define, Measure, Analyze, Improve, Contro/)

In other words … HOW PERFECTLY ARE YOU DOING YOUR CUSTOMER-FOCUSED WORK?

Step 6:

Ensure continuous improvement by measuring, analyzing and controlling the improved process from Step #5

 

What Is Six Sigma and the 1.5 shift?
The Original Concepts And Theories

To quote a Motorola hand out from about 1987 …

‘The performance of a product is determined by how much margin exists between the design requirement of its characteristics (and those of its parts/steps), and the actual value of those characteristics. These characteristics are produced by processes in the factory, and at the suppliers.

Each process attempts to reproduce its characteristics identically from unit to unit, but within each process some variation occurs. For more processes, such as those which use real time feedback to control outcome, the variation is quite small, and for others it may be quite large.

A variation of the process is measured in Std. Dev, (Sigma) from the Mean. The normal variation, defined as process width, is +/-3 Sigma about the mean.

Approximately 2700 parts per million parts/steps will fall outside the normal variation of +/- 3 Sigma. (see chart #2) This, by itself, does not appear disconcerting. However, when we build a product containing 1200 parts/steps, we can expect 3.24 defects per unit (1200 x .0027), on average. This would result in a rolled yield of less than 4%, which means fewer than 4 units out of every 100 would go through the entire manufacturing process without a defect. (see chart #3)Thus, we can see that for a product to be built virtually defect-free, it must be designed to accept characteristics which are significantly more than +/- 3 sigma away from the mean.

It can be shown that a design which can accept TWICE THE NORMAL VARIATION of the process, or +/- 6 sigma, can be expected to have no more than 3.4 parts per million defective for each characteristic, even if the process mean were to shift by as much as +/- 1.5 sigma (see chart #2) In the same case of a product containing 1200 parts/steps, we would now expect only only 0.0041 defects per unit (1200 x 0.0000034). This would mean that 996 units out of 1000 would go through the entire manufacturing process without a defect. To quantify this, Capability Index (Cp) is used; where:

Design Specification Width

Capability Index Cp =

Process Width

A design specification width of +/- 6 Sigma and a process width of +/- 3 Sigma yields a Cp of 12/6 = 2. However, as shown in (see chart #4), the process mean can shift. When the process mean is shifted with respect to design mean, the Capability Index is adjusted with a factor k, and becomes Cpk. Cpk = Cp(1-k), where:

Process Shift
k Factor =
Design Specification Width

The k factor for a +/- 6 Sigma design with a 1.5 Sigma process shift …

1.5/(12/2) or 1.5/6 = 0.25

and the

Cpk = 2(1- 0.25)=1.5

…’

Also see RTY – Rolled throughput yield.

NOTE: Our software always calculates sigma. It only estimates sigma when calculating control limits for the X Bar and Range control charts.

These concepts are what our software was designed around. And our software allows you to grow from 3 to 6 sigma in .5 sigma steps.

You need to see how to Interpret the Histogram and Capability Indices and how Cpk compares to PPM in order to understand what Six Sigma is all about. And remember, Six Sigma depends on one’s process being in statistical control according to WECO, (Western Electric Company), rules.

 


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Last Updated: Saturday, 10-Jun-06 15:50:57 PDT

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