Use Lean Six Sigma for Efficiency & Quality Improvement
October 27, 2023Comments
The Six Sigma quality-system methodology developed by Motorola in the early 1980s uses statistical analysis to guide process improvements.
The Six Sigma quality-system methodology developed by Motorola in the early 1980s uses statistical analysis to guide process improvements. The term originates from a well-controlled process with a tolerance band within six standard deviations (±6σ) from the center line. A Six-Sigma-capable process will have Cp and Cpk (centered and non-centered stable process capabilities, respectively) measuring at least 2.0 and a maximum of 3.4 defects/million opportunities over the long term. This equates to 99.99966-percent defect-free operations.
The statistical term sigma refers to the standard deviation of a process around its mean on a normal distribution. Although sigma represents variation, it says nothing about acceptability. An attribute with a small sigma outside of the acceptable range always is defective. Similarly, an attribute possessing a large sigma reflects a large range of likely values. However, if it is not a key input variable to the process, then it may always be acceptable regardless of the variation.
Companies deploying the Six Sigma model aim to eliminate defects while driving toward six standard deviations between the mean and the nearest limit in any process. DMAIC (define, measure, analyze, improve and control) is a continuous-process-improvement methodology in widespread use, and provides a framework to achieve this goal. (Refer to the October 2023 issue of MetalForming for a DMAIC overview.)
