Six Sigma Overview
•The Six Sigma model is a highly disciplined approach that helps companies focus on developing and delivering near-perfect products and services. It is based on the statistical work of Joseph Juran, a pioneer of quality management who became revered in Japan.
•The word "Sigma" is a Greek letter used for a statistical term that measures how far a given process deviates from perfection (standard deviation). •The higher the sigma number, the closer to perfection. One sigma is not very good, six sigma means only 3.4 defects per million.
•The central idea behind Six Sigma is that if you can measure how many "defects" you have in a process, you can systematically figure out how to eliminate them and get as close to "zero defects" as possible.
Six Sigma History
•‘Invented’ in 1986 in Motorola by Bill Smith
–Saved Motorola from going out of business
–500% growth in sales in 10 years
–Savings of $14bn
Taken up by Allied Signal/Honeywell in early 90’s (Larry Bossidy)
–Saving $600m per year
–6% productivity increase
–Profit margin increased to 13%
Taken up by GE in 1995 & publicised by Jack Welch
–$750m savings in 3 years
–Operating margins increased from 10 to 15%
Six Sigma Statistics
Shown below are the failure rates (defects per million opportunities, or DPMO) for various sigma levels
Note that the failure rate for 'true' 6 sigma is 0.002 ppm. The commonly used headline figure of 3.4 ppm failures arises because a 1.5 sigma mean shift was introduced to take account of process drift over time in typical manufacturing processes, e.g. due to tool wear.
Six Sigma Doctrine
Six Sigma doctrine asserts that:
Features that set Six Sigma apart from previous quality improvement initiatives include:
Six Sigma Process
The Six Sigma process follows 5 steps, called DMAIC
Six Sigma Tools
A comprehensive set of tools is available for use in Six Sigma projects. For more information, click here.
Six Sigma Commentary
•Typically focussed on Manufacturing Processes
•Typically expressed as Defects per ‘Opportunity’ (DPO), rather than overall defects
•This means defects per process, or per tolerance etc. Each ‘opportunity’ is a different way something can go wrong, or be out of specification. However, overall defects depend on DPO and number of opportunities
•If have 3.4 DPMO (6s on an ‘Opportunity’ basis), but each unit has 1000 opportunities for failure, the customer sees a failure rate of 3400ppm. Is this really a 6s product and company or only a 4s company?
It is characterised by a hierarchy of qualifications from Yellow Belt to Master Black Belt and this has engendered a huge industry in training and consultancy.
Over time the Six Sigma term has been hijacked by management consultants and applied to almost anything, to the point of becoming meaningless.
Also there has been a coming together with Lean philosophy, resulting in the hybrid Lean Six Sigma, which takes the best elements of both approaches and combines them into one. See Lean Six Sigma.
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