SIX SIGMA
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Six Sigma is a rigorous methodology to improve process capability. This process is known as:
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D M A I C
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- Define the Problem
- Measure the Current State
- Analyze Information to Determine Significant Factors
- Improve the Process
- Control the Future State
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| Improving Process Capability |
| Process Capability refers to how well your process produces products to your customer's specifications. Customers define specifications, known as Voice of the Customer; process behavior is the Voice of the Process. |
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| Sigma is simply the Greek symbol for standard deviation. Sigma level can be thought of as the number of standard deviations the average process output is from the nearest specification limit. Therefore, a 6 Sigma process could fit 6 standard deviations between the process average and the nearest specification limit. |
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| Below is an example of a 3-Sigma process. Assuming long-term capability, this process would be expected to produce about 3 defects per thousand opportunities. |
Below is an example of a 6-Sigma process. Assuming long-term capability, this process would be expected to produce about 3.4 defects per million opportunities. |
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| Six Sigma is often misunderstood and applied incorrectly. There is absolutely no better methodology for consistently reducing common-cause variation. That is the key, though; you must be using Six Sigma for variation reduction in stable processes. A stable process is in statistical control (SPC), or only random (a.k.a. common cause) variation exists. |
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| If your processes are not stable, before applying Six Sigma you must first stabilize using Lean strategies: Kaizen, A3, 5 Why's, level load, kanbans, reduce inventory, etc. |
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| Your processes are in one of these four states: |
Ideal State
Conformance to specifications
Predictable output
Stable process
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Threshold State
Nonconformance to specifications
Predictable output
Stable process
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Brink of Chaos
Conformance to specifications
Unpredictable output
Unstable process
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State of Chaos
Nonconformance to specifications
Unpredictable output
Unstable process
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| Six Sigma is the correct methodology for reducing variation in the top two states, the ideal state and the threshold state. |
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| Too many companies try to apply Six Sigma to the bottom two states; it is mathematically incorrect and won't work. Don't fall into this trap. |
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DMAIC Reviewers Guide
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