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Author's profile photo Former Member

Calculation of Standard deviation, Cp & Cpk in SPC

Foe below result achieved see calculation of how Mean Value, Standard deviation, Cp & Cpk is calculated in standard SAP

SPC calculation 1.jpg

See below result of Mean Value, Standard deviation, Cp & Cpk is calculated in standard SAP

SPC calculation 2.jpg

From above screen I have taken below reading

SPC calculation 3.jpg

1. Calculation of Mean value

So Mean Value,    = (Sum of Recorded Result) / No. of Record

                         

SPC calculation 4.jpg

          Mean Value     = 38.667                       

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SPC calculation 6.jpg                     

The mean (38.667) is closer to one of them than to the other, leading to a Cpk factor (0.17) that is lower than the Cp value (0.22). This implies that the LSL is more difficult to achieve than the USL. Non-conformities exist at both ends of the histogram.

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      6 Comments
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      Author's profile photo Former Member
      Former Member

      good example on calculating Cp, CpK.

      Author's profile photo Ramagiri Srinivas Rao
      Ramagiri Srinivas Rao

      Hi Rajesh,

      Good one. What master data settings are maintained to calculate mean, Cp and Cpk?

      Thanks & Regards,

      Ramagiri

      Author's profile photo Zhao Mishuang
      Zhao Mishuang

      Most of it is statistics knowledge.

      Author's profile photo Mariusz Gach
      Mariusz Gach

      How do you display Process Capability window for given results?

      Author's profile photo Dipeshkumar Bhavsar
      Dipeshkumar Bhavsar

      Hi Rajesh,

      Good Documents.

      Regards,

      Dipeshkumar Bhavsar

      Author's profile photo Former Member
      Former Member

      Hi,

      How do to select USL and LSL limits?

      For example,

      I have measured results of 30 samples Re is 3.43, 3.27 ,3.19, 3.17,3.17, 3.19, 3.19, 3.24, 3.1, 3.12 ,3.25, 3.2, 3.35, 3.2, 3.2, 3.22, 3.23, 3.18, 3.19, 3.31, 3.18, 3.08, 3.18, 3.17, 3.23, 3.19, 3.25, 3.26, 3.23, 3.18

      mean = 3.2117, STD = 0.07

      Company datasheet provided for Re is 3.08 and production tolerances +/- is 7.50%

      ——–
      to find Cpk how do I calculate USL and LSL values?

      Actually, which is the target value?