Sigma is the 18th letter of the Greek alphabet and among other things, the lower case representation is used to denote the Standard Deviation of a population or Probability Distribution in Statistics. In simple terms, this denotes how much of a deviation there is from the perfect situation.
Enough already about plain Sigma, now let's look at Six Sigma.
Six Sigma is a set of data-driven tools and strategies for improving processes - originally developed by Motorola in 1985. It became more popular after Jack Welch made it the standard process to be used in GE in 1995.
The main philosophy behind Six Sigma is to use a data driven approach to measure the number of defects in the process and then figure out a way to systematically reduce them as close to zero as possible. To achieve Six Sigma quality, the defects should be reduced to less than 3.4 per million opportunities. Say for example, if a million parts are produced by a factory in a week, then it would be running at Six Sigma if less than 3.4 (3 or less) parts turn out to be defective in that week.
It was originally intended for improving existing manufacturing processes but later on enhanced to have a methodology for designing new processes as well.
The two methodologies which are composed of five phases each, are (quoted from Wikipedia):
DMAIC : used for improving an existing process.
DFSS / DMADV : used for creating/designing new product or process.
DMAICThe DMAIC project methodology consists of the following five phases:
Define the problem and the project goals, specifically.
Measure key aspects of the current process and collect relevant data.
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 experiments, poka 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 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.
DMADV / DFSSThe DMADV methodology is also known as DFSS - "Design For Six Sigma" and consists of the following five phases:
Define design goals that are consistent with customer demands and the enterprise strategy.
Measure and identify CTQs (characteristics that are Critical To Quality), product capabilities, production process capability, and 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).
Six Sigma denotes four roles for its successful implementation as shown below:
Executive Leadership or top management who are responsible for creating the Six Sigma vision and to empower the employees to bring about this change.
Champions who take responsibility for Six Sigma implementation across the organization in an integrated & consistent manner and also identifying projects/functions for Six Sigma.
Master Black Belts who act as in-house coaches on Six Sigma & devote all their time only to Six Sigma. They assist Champions and guide Black Belts & Green Belts and work on ensuring consistent application of Six Sigma across various functions and departments.
Black Belts operate under Master Black Belts to apply Six Sigma methodology to specific projects and devote all their time to application & execution of Six Sigma for specific projects.
Green Belts are the employees who take up Six Sigma implementation along with their other job responsibilities and work under the guidance of Black Belts.