Section II: Six Sigma
What is Six Sigma?
Six Sigma is a structured data-driven problem-solving methodology. The focus is on process variations and emphasis is given to customer satisfaction. The purpose of this method is continuous process improvement with low defects.
The goal of Six Sigma:
The goal of Six Sigma is to make a process effective that is 99.99996% defect free. This means that a six sigma process produces 3.4 defects per million opportunities, or less, as a result. Problem-solving in Six Sigma is done using the DMAIC framework. There are five stages in this framework. These are:
- Improve, and
Figure 3: The DMAIC Roadmap
Six Sigma Phase
Description of Phase
In this stage, project objectives are outlined. A project charter is an important component of this phase. It is a blueprint document for a six sigma project. A typical charter contains the following information:
- Business case
- Problem statement
- Goal statement
- Project scope
- Estimated benefits
This charter gives an overview of a six sigma project and is approved by top management to give a go-ahead for the six sigma project.
Process variables are measured at this stage. Process data is collected, the baseline is obtained and metrics are compared with final performance metrics. Process capability is obtained.
Root cause analysis is done at this stage. Complex analysis tools are utilized to identify the root causes of a defect. Tools like histograms, Pareto charts, fishbone diagrams are used to identify the root causes. Hypotheses tests are conducted to verify and validate root causes, e.g., Regression test, ANOVA test, Chi-square etc.
Once final root causes are identified, solutions need to be formed to improve the process. Steps to identify, test and implement the solutions to eliminate root causes are part of this stage. Simulation studies, Design of experiments, Prototyping are some of the techniques used here to improve and maximize process performance.
After implementing the solutions, the performance of the solutions must be recorded. A control system must be in place to monitor the performance post improvement. And a response plan is developed to handle solution failure. Process standardization through control plans & work instructions is typically a part of this phase. Control charts show the process performance. Project benefits are discussed and verified against estimated one. The main purpose of this phase is to ensure the holding of the gains.
Table 2: Six Sigma Phases and their descriptions
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