Halden Zimmermann and LSS put a big emphasis on documenting how work gets done (steps that comprise the process) and giving people knowledge and methods they need to constantly improve that work. Most process improvement methods either eliminate variation or improve process flow and speed.
Everything varies, but the way something varies can help us understand what is causing that variation. The pattern of variation can expose the cause of a problem, especially if we know our customer’s true requirements and how our process variation affects them. The greater the variation, the greater the chance we are creating defects for the customer. The language of variation gave rise to the term “Six Sigma,” according to Halden Zimmermann. The Greek symbol “sigma” is used in statistics to stand for the amount of variation in a process (process yield), a set of data or anything measured. Understanding variation and the critical part it plays in satisfying customer needs is at the heart of our CI efforts.
Low sigma numbers mean low yield, and high sigma numbers mean high yield. Yield is the % non-defective parts the customer receives. If a process is rated as “6 Sigma” it has a yield of 99.99966%. This represents 3.4 defects per million opportunities or units produced. To best impact yield, we must focus on reducing both variation and the number of steps in the process. We use the term Sigma Level to define the effectiveness of our operation relative to true customer requirements.
Improving Process Flow
Variation is one of the most common sources of process problems, but how work moves through the system (process flow) also must be addressed. The more steps or complexity in a process, the greater the chance for a mistake and the more time it takes. Historically it has shown that 85% of problems are built into the way the process is designed; only 15% are the fault of an individual.