Business Considerations - Fundamentals of Industrial Chemistry: Pharmaceuticals, Polymers, and Business - page 65

per million opportunities. For the phones, we have one defect per 25,000
opportunities or 40 defects per million opportunities. This value is probably
more representative of the quality of the manufacturing processes. We can
account for the complexity of the products and the number of specifications
by considering the value of defects per million opportunities or DPMO.
There is typically less variation in a short period of time than in a longer
period of time. To account for this longer term process variability, an
empirically-based 1.5 sigma shift is introduced into the calculation. Based
upon this idea, a process that fits six sigma between the process mean and
the nearest specification limit in a short-term study will in the long term fit
only 4.5 sigma. A process that is termed a six sigma process is more strictly
speaking a 4.5 sigma process. There are charts [1] that correlate DPMO
with the capability of the process. A process that has 3.4 DPMO is a six
sigma process. In contrast, a three sigma process has 66,800 DPMO. The
goal of a six sigma program is to reduce process defects to a level of 3.4
DPMO. At first, this might seem too intense. Why not target four sigma? A
process running at four sigma has 99.4% of its output defect free. That may
sound good, but not when you focus on DPMO. The DPMO of a four sigma
process is 6,210. If operating at four sigma, every hour the post office would
lose 20,000 pieces of mail and every week, there would be 5,000 surgical
operations that go wrong in some way [2].
Six Sigma is a method to reduce variation and therefore the number of
defects to a level of 3.4 DPMO. Six Sigma uses statistical tools to identify
the important factors that can improve the quality of the processes. There are
five important phases [3]: 1. Define the projects, goals, and deliverables to
customers; 2. Measure the current performance of the process; 3. Analyze
and determine the root cause of the defects; 4. Improve the process to
eliminate defects; and 5. Control the performance of the process. These
phases go by the acronym DMAIC. In the Define phase [4], the goals of
the improvement activity are determined. These could come from internal
or external customers or could be strategic objectives of the organization or
improved throughput and reduced defects. In the Measure phase, valid and
reliable metrics are established to monitor progress toward the goal. In the
Analyze phase, ways to eliminate the gap between current performance and
desired goal are explored using statistical analysis. In the Improve phase,
new ways to do things are implemented and statistical methods are used to
validate the improvement. The statistical tools are then used in the Control
phase to monitor the stability of the new system. Policies, procedures, and
documentation are implemented to enforce the new process.
Implementation of Six Sigma involves people throughout the organization
and the training of many people. Sometimes their roles are given names
such as “Black Belts” or “Green Belts”, based upon the amount of training