Updated: Sep 23
Six Sigma is a trademarked methodology for quality control. It seeks to improve processes by removing causes of defects and minimizing process variability. Six Sigma is also often combined with lean manufacturing (called Lean Six Sigma) but I will cover lean manufacturing as a separate topic. The name Six Sigma comes from statistical quality control. Sigma denotes standard deviation (STD) from the mean where the mean represents the desired output. Six Sigma is derived from using an Upper and Lower Specification Limit that is 6 STDs away from the mean. This creates a safety margin even if a plus or minus 1.5 STD shift of the mean exists. A Six Sigma standard would bring defect levels to below 3.4 defects per million opportunities (DPMO). Having a high-quality process control will not only improve product quality but also result in cost savings by reducing process disruption, investigations, rework, duplication, and reverse logistics.
The Six Sigma methodology follows five steps known as DMAIC:
Define – this specifies the problem or process to be addressed
Measure – collect data, quantify and provide a baseline for the defined process
Analyze – identify and determine the root cause of problems
Improve – identify, test, and implement solutions to problems or elimination of the root cause from the previous step.
Control –ensure the changes are made and sustained. It may involve continued monitoring and setting up of control systems to solidify changes.
There are many tools and methods within each of these steps that may be utilized and no two projects/processes will look the same. The process takes a lot of skill and should be executed by a person with Six Sigma certification. The certification has multiple levels. They usually include white, yellow, green, black, and master black belts. There are many organizations awarding certification. I would love your recommendations and input with regard to certification in the comment section below if you are familiar with the process.