Six Sigma:

Motorola developed a concept called “Six Sigma Quality” that focuses on defect rates, as opposed to percent performed correctly. “Sigma” is a statistical term meaning one standard deviation. “Six Sigma” means six standard deviations. At the Six Sigma statistical level, only 3.4 items per million are outside of the acceptable level. Thus, the Six Sigma quality level means that out of every one million items counted 999,996.6 will be correct, and no more than 3.4 will be defective.

Experience has shown that in most systems, a Four Sigma quality level is the norm. At the Four Sigma level there are 6,120 defects per million parts, or about 6 defects per 1,000 opportunities, to do a task correctly.
Six Sigma asserts the following:
• Continuous efforts to reduce variation in process outputs is key to business success
• Manufacturing and business processes can be measured, analyzed, improved and controlled
• Succeeding at achieving sustained quality improvement requires commitment from the entire organization, particularly from top-level management
Six Sigma has two key methodologies: DMAIC and DMADV. DMAIC is used to improve an existing business process, and DMADV is used to create new product or process designs for predictable, defect-free performance.
DMAIC
Basic methodology consists of the following five steps:
• Define the process improvement goals that are consistent with customer demands and enterprise strategy.
• Measure the current process and collect relevant data for future comparison.
• Analyze to verify relationship and causality of factors. Determine what the relationship is, and attempt to ensure that all factors have been considered.
• Improve or optimize the process based upon the analysis using techniques like Design of Experiments.
• Control to ensure that any variances are corrected before they result in defects. Set up pilot runs to establish process capability, transition to production and thereafter continuously measure the process and institute control mechanisms.
DMADV
Basic methodology consists of the following five steps:
• Define the goals of the design activity that are consistent with customer demands and enterprise strategy.
• Measure and identify CTQs (critical to qualities), product capabilities, production process capability, and risk assessments.
• Analyze to develop and design alternatives, create high-level design and evaluate design capability to select the best design.
• Design details, optimize the design, and plan for design verification. This phase may require simulations.
• Verify the design, set up pilot runs, implement production process and handover to process owners.