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Six Sigma () is a set of techniques and tools for process improvement. It was introduced by engineer Bill Smith while working at Motorola in 1986.[1][2] Jack Welch made it central to his business strategy at General Electric in 1995.

It seeks to improve the quality of the output of a process by identifying and removing the causes of defects and minimizing variability in manufacturing and business processes. It uses a set of quality management methods, mainly empiricalstatistical methods, and creates a special infrastructure of people within the organization who are experts in these methods. Each Six Sigma project carried out within an organization follows a defined sequence of steps and has specific value targets, for example: reduce process cycle time, reduce pollution, reduce costs, increase customer satisfaction, and increase profits.

The term Six Sigma (capitalized because it was written that way when registered as a Motorola trademark on December 28, 1993) originated from terminology associated with statistical modeling of manufacturing processes. The maturity of a manufacturing process can be described by a sigma rating indicating its yield or the percentage of defect-free products it creates. A six sigma process is one in which 99.99966% of all opportunities to produce some feature of a part are statistically expected to be free of defects (3.4 defective features per million opportunities). Motorola set a goal of "six sigma" for all of its manufacturing.

 

 



The common Six Sigma symbol





Six Sigma doctrine asserts:


  • Continuous efforts to achieve stable and predictable process results (e.g. by reducing process variation) are of vital importance to business success.
  • Manufacturing and business processes have characteristics that can be defined, measured, analyzed, improved, and controlled.
  • Achieving sustained quality improvement requires commitment from the entire organization, particularly from top-level management.

Features that set Six Sigma apart from previous quality-improvement initiatives include:


  • A clear focus on achieving measurable and quantifiable financial returns from any Six Sigma project.
  • An increased emphasis on strong and passionate management leadership and support.
  • A clear commitment to making decisions on the basis of verifiable data and statistical methods, rather than assumptions and guesswork.

The term "six sigma" comes from statistics and is used in statistical quality control, which evaluates process capability. Originally, it referred to the ability of manufacturing processes to produce a very high proportion of output within specification. Processes that operate with "six sigma quality" over the short term are assumed to produce long-term defect levels below 3.4 defects per million opportunities (DPMO). The 3.4 dpmo is based on a "shift" of +/- 1.5 sigma created by the psychologist Dr Mikel Harry. He created this figure based on the tolerance in the height of a stack of discs.[3][4] Six Sigma's implicit goal is to improve all processes, but not to the 3.4 DPMO level necessarily. Organizations need to determine an appropriate sigma level for each of their most important processes and strive to achieve these. As a result of this goal, it is incumbent on management of the organization to prioritize areas of improvement.

"Six Sigma" was registered June 11, 1991 as U.S. Service Mark 1,647,704. In 2005 Motorola attributed over US$17 billion in savings to Six Sigma.[5]

Other early adopters of Six Sigma include Honeywell and General Electric, where Jack Welch introduced the method.[6] By the late 1990s, about two-thirds of the Fortune 500organizations had begun Six Sigma initiatives with the aim of reducing costs and improving quality.[7]

In recent years, some practitioners have combined Six Sigma ideas with lean manufacturing to create a methodology named Lean Six Sigma.[8] The Lean Six Sigma methodology views lean manufacturing, which addresses process flow and waste issues, and Six Sigma, with its focus on variation and design, as complementary disciplines aimed at promoting "business and operational excellence".[8] Companies such as GE,[9] Accenture, Verizon, GENPACT, and IBM use Lean Six Sigma to focus transformation efforts not just on efficiency but also on growth. It serves as a foundation for innovation throughout the organization, from manufacturing and software development to sales and service delivery functions.

The International Organization for Standardization (ISO) has published in 2011 the first standard "ISO 13053:2011" defining a Six Sigma process.[10] Other "standards" are created mostly by universities or companies that have so-called first-party certification programs for Six Sigma.

 

 

Methodologies

 

Six Sigma projects follow two project methodologies inspired by Deming's Plan-Do-Check-Act Cycle. These methodologies, composed of five phases each, bear the acronyms DMAIC and DMADV.[7]


  • DMAIC ("duh-may-ick", /dʌ.ˈmeɪ.ɪk/) is used for projects aimed at improving an existing business process.[7]
  • DMADV ("duh-mad-vee", /dʌ.ˈmæd.vi/) is used for projects aimed at creating new product or process designs.[7]

 

DMAIC



The five steps of DMAIC





Main article: DMAIC

The DMAIC project methodology has five phases:

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  • Define the system, the voice of the customer and their requirements, and the project goals, specifically.
  • Measure key aspects of the current process and collect relevant data; calculate the 'as-is' Process Capability.
  • Analyze the data to investigate and verify cause-and-effect relationships. Determine what the relationships are, and attempt to ensure that all factors have been considered. Seek out root cause of the defect under investigation.
  • Improve or optimize the current process based upon data analysis using techniques such as design of experimentspoka yoke or mistake proofing, and standard work to create a new, future state process. Set up pilot runs to establish process capability.
  • Control the future state process to ensure that any deviations from the target are corrected before they result in defects. Implement control systems such as statistical process control, production boards, visual workplaces, and continuously monitor the process. This process is repeated until the desired quality level is obtained.

Some organizations add a Recognize step at the beginning, which is to recognize the right problem to work on, thus yielding an RDMAIC methodology.[11]

DMADV or DFSS



The five steps of DMADV


Main article: DFSS

The DMADV project methodology, known as DFSS ("Design For Six Sigma"),[7] features five phases:

  • Define design goals that are consistent with customer demands and the enterprise strategy.
  • Measure and identify CTQs (characteristics that are Critical TQuality), measure product capabilities, production process capability, and measure risks.
  • Analyze to develop and design alternatives
  • Design an improved alternative, best suited per analysis in the previous step
  • Verify the design, set up pilot runs, implement the production process and hand it over to the process owner(s).




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