The first application of Six Sigma in the industry was at Motorola in 1986, where it found use to improve the manufacturing process and eliminate product defects. Since then, the method has found widespread acceptance in many other business processes.
The inspiration for Six Sigma came from earlier approaches towards quality such as Total Quality Management, Zero Defects, Schewart's cycle, and others. It differs from such other quality improvement initiatives by its mathematically intensive nature. Six Sigma use statistical techniques to detect undesirable variations in process and product performance, and strives to limit variations to 3.4 defects per million opportunities. The term “Sigma" stands for standard deviation from the mean in a normal distribution, and "Six Sigma" refers to the desired state of a process outside the six statistical deviations.
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The general Six Sigma approach involves:
- Identification of the undesirable process or product variation
- Defining the statistical scope and parameters of the problem
- Developing and applying initial measures of process or product variability
- Collecting and analyzing data to pinpoint the causes of variation
- Developing a time bound action plan for improving the process
- Implementing the improvements
- Ensuring that the changes remain without a relapse to the previous state
Such an apprach to implement Six Sigma takes place through the DMAIC (Define, Measure, Analyze, Implement, and Control) or DMADV (Design, Measure, Analyze, Design, Verify) process.
DMAIC, used to implement Six Sigma in existing processes stands for:
- Define: defining project scope, resources, and timelines
- Measure: quantifying and benchmarking the process using actual data
- Analyze: applying statistical tools to validate root causes of problems. The tools used include Failure Mode Effective Analysis (FMEA), Analysis of Variance (ANOVA), and others.
- Improve: identifying solutions to the problems using tests and experiments
- Control: establishing metrics and control charts to prevent roll back
DMADV finds application to implement Six Sigma in new processes. Of the Six Sigma steps in DMADV, Define, Measure, and Analysis remains the same. DMADV incorporates a Design phase to incorporate feedback instead of the Improve phase, and Verification phase to replace the Control phase.
Implementation of Six Sigma requires a special purpose team trained in Six Sigma step and concepts.
Six Sigma Champions are business leaders who lead the Six Sigma methodology by selecting projects. Such champions select and mentor Six Sigma project leaders, referred to by their “belt" which indicates to the level or the position in Six Sigma competency of such person at the time of project implementation.
- Green Belt: those qualified to implement Six Sigma under supervision of Black Belts
- Black Belt: those competent to explain six sigma philosophies and principles, and use specific Six Sigma tools
- Master Black Belt: six sigma quality experts responsible for strategic implementations within an organization, and training and mentoring of black belts and the green belts.
- Yellow Belt: those having overall insight to Six Sigma management techniques.
Special purpose teams such as inventory reduction team, manufacturing scrap reduction team and others formed specifically for implementing Six Sigma usually have Green Belts led by a Black Belt or Master Black Belt. Such a team remains exclusively responsible for the implementation of Six Sigma, and they may choose to involve others at their discretion.
Lean Six Sigma
The Lean philosophy of quality improvement aims at identifying and eliminating non-essential and non-value adding activities to improve process flow and enhance productivity.
Six Sigma dovetails with lean, and the Lean Six Sigma approach entails using lean methodologies to identify and remove non-value adding activities and processes, and then applying Six Sigma methodologies to identify and eliminate process variation. Len Six Sigma also involves the combination of Six Sigma management techniques and Lean tools such as 5S, Kanban, poka-yoke, value stream apping and others in the DMAIC or DMADV process.
One major criticism levied against Six Sigma is that it concerns itself with only the specific process, without looking into the bigger scheme of things, and specifically that the Six Sigma changes do not permeate to the entire organization. While this holds true in theory, the need for perfection means that most Six Sigma program invariably include not just a specific department, but the entire processes that matter. In a similar vein, the need for all round perfection induced by competition make Six Sigma teams involve everyone involved in the process to strive for continuous, unrelenting improvement. Success in this count however depends on the extent to which leadership aligns Six Sigma initiatives with organizational priorities.
An effective Six Sigma approach improves customer response time, cut cycle times, and improves product quality, leading to overall customer satisfaction.