Statistical Process Control (SPC)

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Six Sigma Methodology | Six Sigma Model | Six Sigma Approach > Best Practices > Statistical Process Control (SPC)

Statistical Process Control (SPC)
Fred Allen
According to many, Six Sigma is based on Statistical Process Control (SPC), a method of visually monitoring production processes. In Six Sigma, each business process must be measured and for this often the SPC methodology is used. Aims of SPC are: 1. Adjustment: To detect quickly when a process needs readjustment or repair. 2. Improvement: To find the most urgently needed improvement in the system itself.
 

 
PC
Alice
What is the difference between PPK & CPK?
 

 
What is the difference between PPK & CPK?"
Lo.Max
PPK is measured by unknowed process, cpk is measured by stable process
 

 
Cpk or Ppk??
Jacques-Alain TIAKO, Manager, France, Member
Cpk - It's the capability index for a stable process (the process must be in a state of statistical control). The sigma calculation is based on within subgroup variation.
Ppk - It's the performance index (the actual process PERFORMANCE). The estimate of sigma is based on total variation. Ppk must be calculated if less than 100 samples or when the process is chronically unstable but meeting the specifications and in a predictable pattern.
 

 
What is the Difference Between PPK & CPK?
Ger de Waard, Management Consultant, Netherlands, SIG Leader
In the Six Sigma quality methodology, process performance is reported to the organization as a sigma level. The higher the sigma level, the better the process is performing.
Another way to report process capability and process performance is through the statistical measurements of Cp, Cpk, Pp, and Ppk.
Definitions
Cp = Process Capability. A simple and straightforward indicator of process capability.
Cpk = Process Capability Index. Adjustment of Cp for the effect of non-centered distribution.
Pp = Process Performance. A simple and straightforward indicator of process performance.
Ppk = Process Performance Index. Adjustment of Pp for the effect of non-centered distribution.
Cp and Cpk are for computing the index with respect to the subgrouping of your data (different shifts, machines, operators, etc.), while Pp and Ppk are for the whole process (no subgrouping).
 

     
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Jagdish B Acharya
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