Six Sigma
Six Sigma,
An improvement Strategy…….
Causes of Variation
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Random, chance, constant, common, unknown causes the “rhythm” of the process ● Variation inherent in a process ● Can be eliminated only through improvements in the system Assignable, special causes ● something has changed ● Variation due to identifiable factors ● Can be modified through operator or management action
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What are the sources of variation in a process?
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Machine variation Raw Material variation Different methods used Measurement variation Operator variation Environmental factors
Assignable Causes of Variation:
The Backbone of Six-sigma
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Examples of things that may be assignable causes of variation:
● ● ● ● ●
machine troubles (damaged saw teeth, plugged blowpipe, etc.) faulty measuring device operator overcontrol worker fatigue drastic changes in raw material
Random, chance variation:
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“4M’s and OE”
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Machine Material Method Measurement Operator Environment
Process Capability
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The range of “natural variability” in a process is measured with control charts. A Process cannot meet specifications (customer expectations) if natural variability exceeds tolerances (specification limits) 3-sigma quality
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specifications equal the process control limits. specifications twice as large as control limits
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6-sigma quality
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Process Capability
PROCESS Natural control limits
Design specifications
Process cannot meet specifications because the variability of the process is greater than allowed by design specifications
Process Capability
PROCESS
Natural control limits
Design specifications
Process can meet specifications exactly
Measuring Process Capability
Measures of process capability tell us whether the process is capable of producing within specifications
●
Cpk = min [(USL - μ)/3 σ, (μ - LSL)/3σ ]
●
If Cpk < 1, the process is not capable of performing within specifications.
An improvement Strategy…….
Causes of Variation
●
Random, chance, constant, common, unknown causes the “rhythm” of the process ● Variation inherent in a process ● Can be eliminated only through improvements in the system Assignable, special causes ● something has changed ● Variation due to identifiable factors ● Can be modified through operator or management action
●
What are the sources of variation in a process?
● ● ● ● ● ●
Machine variation Raw Material variation Different methods used Measurement variation Operator variation Environmental factors
Assignable Causes of Variation:
The Backbone of Six-sigma
●
Examples of things that may be assignable causes of variation:
● ● ● ● ●
machine troubles (damaged saw teeth, plugged blowpipe, etc.) faulty measuring device operator overcontrol worker fatigue drastic changes in raw material
Random, chance variation:
●
“4M’s and OE”
● ● ● ● ● ●
Machine Material Method Measurement Operator Environment
Process Capability
●
●
●
The range of “natural variability” in a process is measured with control charts. A Process cannot meet specifications (customer expectations) if natural variability exceeds tolerances (specification limits) 3-sigma quality
●
specifications equal the process control limits. specifications twice as large as control limits
●
6-sigma quality
●
Process Capability
PROCESS Natural control limits
Design specifications
Process cannot meet specifications because the variability of the process is greater than allowed by design specifications
Process Capability
PROCESS
Natural control limits
Design specifications
Process can meet specifications exactly
Measuring Process Capability
Measures of process capability tell us whether the process is capable of producing within specifications
●
Cpk = min [(USL - μ)/3 σ, (μ - LSL)/3σ ]
●
If Cpk < 1, the process is not capable of performing within specifications.