Six Sigma Process Capability-Minitab Process Capability Analysis • Control Charts measures how the process is performing • The Process Capability Analysis attempts to measure the process in terms of meeting customer requirements • Capability Analysis looks at the mean of the process compared to the target and the Upper and Lower Control Limits as compared to the Upper and Lower Specification Limits. Process Capability Analysis • Use When – Control Chart indicates Process is “in control” – Data has Normal Distribution and is Continuous (Variable). – Measuring Process to Requirements – Comparing two processes to see which meets requirements (i.e. two different machines) – Need data, facts to discuss with Management and/or Customer Process Capability Analysis Process Capability Analysis Process Capability Analysis • • • • Looks somewhat Normal Cp is 1.09 Cpk is 1.06 For a capable process, the larger a number the better. • A Cpk of at least 1.0 is required and a value of 1.33 (both positive) is preferred. • (Really need at least 25 sub-groups) Process Capability Analysis • Difference between Cp and Cpk – Cp needs both lower and upper specifications. Cannot really tell if process is generating defects. – Cpk is more widely used as it measures how much of the production process really conforms to the engineered (customer) specifications. – Pp and Ppk are the longer term capability indexes. Summary Control Chart vs. Capability • Control Charts measure the process in terms of stability; special vs. common causes of variation. • Capability Analysis can only be performed after a process is stabilized and is used to determine if process is meeting customer specifications.
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