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How Does Six Sigma Work

Six Sigma is a disciplined and quantitative approach involving setting up a system and process for the improvement of defined metrics in manufacturing, service, or financial processes. The approach drives the overall process of selecting the right projects based on an organization's business goals and selecting and training the right people to obtain the results. Improvement projects follow a disciplined process defined by a system of four macro phases: measure, analyze, improve, control (MAIC).

Sometimes a preliminary step, define, is added at the beginning, which relates to the appropriate selection of projects and problem definition. The problem must be chronic and impactful.

The 4 MAIC phases will be described as follows:

Measure Phase:
Measure the existing systems. Establish valid and reliable metrics to help monitor progress towards the project goals. Customer expectations are defined to determine “out of specification” conditions.

  • Identify and describe the potential critical processes/products

List and describe all of the potential critical processes obtained from brainstorming sessions, historical data, yield reports, failure analysis reports, analysis of line fallout and model the potential problems.

  • Perform measurement system analysis

Determine precision, accuracy, repeatability and reproducibility of each instrument or gauge used in order to ensure that they are capable.

Analyze Phase:
Analyze the system to identify ways to eliminate the gap between the current performance of the system or process and the desired goal. In this phase, project teams explore underlying reasons for defects. They use statistical analysis to examine potential variables affecting the outcome and seek to identify the most significant root causes. Then, they develop a prioritized list of factors influencing the desired outcome.

  • Isolate and verify the critical processes

Narrow the potential list of problems to the vital few. Identify the input/output relationship which directly affects specific problems. Verify potential causes of process variability and product problems.

  • Perform process and measurement system capability studies

Identify and define the limitations of the processes. Ensure that the processes are capable of achieving their maximum potential. Identify and remove all variation due to special causes. Determine what the realistic specifications are. Determine confidence intervals. A process is to be considered capable when it is in control, predictable, and stable.

Improve Phase:
In this phase, project teams seek the optimal solution and develop and test a plan of action for implementing and confirming the solution. The process is modified and the outcome is measured to determine whether the revised method produces results within customer expectations.

  • Conduct design of experiment

Select design of experiment factors and levels. Plan design of experiment execution. Perform design of experiment to find out the most significant factor.

  • Implement variability reduction designs/assessments

Implement permanent corrective action for preventing special cause variations. Demonstrate process stability and predictability.

Control Phase:
Control the new system. Ongoing measures are implemented to keep the problem from recurring. Institutionalize the improved system by modifying policies, procedures, operating instructions, and other management systems.

  • Specify process control method
    • Establish on-going controls for the process based on prevention of special cause variation using statistical process control techniques.

  • Document the improvement processes

    Record all the processes/steps in improvement phase using the decision tree and reaction plan.

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