Cp, Cpk Formula & Calculations (Cpk > 1.33 is desirable) Cp and Cpk use Sigma Estimator However, if the process is unstable – i.e. if it shifts or drifts over time – you will find Ppk << Cpk. The result comes from the data in Figure 3. Cpk is the potential of a process to meet a specification (short term). 1. In fact, the only difference between these formulas is the use of sigma-hat in the denominators of Cp and Cpk, but sigma in the denominators of Pp and Ppk. P pk tells us how a process has performed in the past and you cannot use it predict the future because the process is not in a state of control. the actual performance will match the predicted potential performance. In other words, how distributed the outcome of your process is vs what the requirements are. When you examine the relationships for both Cpk and Ppk compare the mean, a central tendancy stat, to one side or the other indicating “center”. Cp Cpk Formulas versus Pp Ppk Formulas Formulas for Cp Cpk and Pp Ppk are Similar. The only acceptable formula for Cpk uses the estimated sigma. In 1991, the ASQC/AIAG Task Force published the "Fundamental Statistical Process Control" reference manual, which shows the calculations for Cpk as well as Ppk. Process performance index, is a statistical tool to verify if the sample that have generated from the process is capable to meet the customer requirement. Differences Between Cpk and Ppk. PPK vs CPK . Sowohl PPK als auch CPK haben sehr weitreichende Auswirkungen auf die Leistungsstrategie von … Cpk vs Ppk - Which should you use and How to Calculate Cpk and Ppk: Statistical Analysis Tools, Techniques and SPC: 25: Feb 26, 2007: V: Quality Control Index - We thought that Cpk or Ppk would be good choices: Capability, Accuracy and Stability - Processes, Machines, etc. Given that Ppk uses the calculated sigma, it is no longer necessary to use the calculated sigma in Cpk. Ppk uses "s-long-term" to evaluate the behavior of the process. 2. Ppk is how the process actually did (long term). It measures the performance of the process related to both dispersion and centeredness. However, the difference for Cpk is (3.13 vs. 1.39) +125%! If the process is stable, Ppk = Cpk, i.e. Cpk vs Ppk. It is used to measure the potential capability of a system to meet customer needs. Figure 6: Calculation of Cpk, Ppk with (30) Data Points. Cpk calculates the standard deviation of each subgroup and pools the results, whereas Ppk calculates the standard deviation from all data as one continuous matrix. It is most important to understand the basic relationships and memorize the most common levels of sigma, Cpk, and yield for normal distributions. Also, Cpk is estimated from the sigma level and it isn't always an exact match since the Cpk calculation takes the better of the USL or LSL and doesn't consider the tail of the opposite tail. Process Performance Index (Ppk, Cpk, Pp) x. PPK und CPK sind hauptsächlich Prozessfähigkeitsindizes. It is used to measure the performance of a system to meet customer needs. Please explain why Pp and Cp are referred to as “centralized” rates, and Cpk and Ppk are referred to as “unilaterial” rates in paragraph 5 of this article. (Figure 6). People often get confused about the difference between Pp/Ppk and Cp/Cpk. Wenn PPK für Process Performance Index steht, steht CPK für Process Capability Index.

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