These calculators compute the process capability index (Cp, Cpk) which shows the process potential of meeting the specifications. Enter the process parameters and specifications in one of the following tables, depending on whether you have a double-sided or single-sided specification.
Historical note: “Six sigma” really started with Cpk… Motorola wanted to tolerate process shifts (i.e., changes in the process mean) of up to 1.5σ in either direction but still wanted to ensure a low defect rate. If the USL and LSL are both set to be 6σ (six sigma!) away from the mean, then a maximal process shift of 1.5σ would still produce the magical number of 3.4 defective parts per millions (PPM).
The result is :
Process Capability Index
Double-sided specification
- The upper specification limit (USL) = 300.000000
- The lower specification limit (LSL) = 100.000000
- The standard deviation = 37.000000
- The mean = 186.000000
The actual process capability is Cpk = 0.775
The potential process capability is Cp = 0.901
The potential process capability can be achieved by centering the process
The PPM calculations are for the potential process capability
The process fallout is approximately 6934 PPM (defective parts-per-million)
For an existing process, the Cp is below the recommended minimum (1.33)
For a new process, the Cp is below the recommended minimum (1.50)
For an existing critical process(*), the Cp is below the recommended minimum (1.50)
For a new critical process(*), the Cp is below the recommended minimum (1.67)
(*) Examples of critical processes are ones related to safety, strength etc.
Continue at: https://www.sqconline.com/process-capability-index-0
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