Process Capability Cp, Cpk and Process Performance Pp, Ppk What is the Difference Process Capability Cp, Cpk and Process Performance Pp, Ppk What is the Difference 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. This article will present definitions, interpretations and calculations for Cpk and Ppk though the use of forum quotations. Thanks to everyone below that helped contributed to this excellent reference. Jump To The Following Sections 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. Interpreting Cp, CpkCpk is an index a simple number which measures how close a process is running to its specification limits, relative to the natural variability of the process. The larger the index, the less likely it is that any item will be outside the specs. Neil PolhemusIf you hunt our shoot targets with bow, darts, or gun try this analogy. If your shots are falling in the same spot forming a good group this is a high Cp, and when the sighting is adjusted so this tight group of shots is landing on the bullseye, you now have a high Cpk. TommyCpk measures how close you are to your target and how consistent you are to around your average performance. A person may be performing with minimum variation, but he can be away from his target towards one of the specification limit, which indicates lower Cpk, whereas Cp will be high. On the other hand, a person may be on average exactly at the target, but the variation in performance is high but still lower than the tolerance band i. QI Macros SPC for Excel Free download and software reviews. Pros. Integrated with Excel. Reasonable cost. Lots of features. Currently, I am working on developing a. SPC for Excel Software Download the Free. Process Capability Cpk. SPC for Excel software. Weve included process capability features that any. I have datas of one process characteristicoutput Y. I would like to calculate Cp and Cpk for that process output but also to generate chart to see distribution of. In such case also Cpk will be lower, but Cp will be high. Cpk will be higher only when you r meeting the target consistently with minimum variation. AjitYou must have a Cpk of 1. Joe PeritoConsider a car and a garage. The garage defines the specification limits the car defines the output of the process. If the car is only a little bit smaller than the garage, you had better park it right in the middle of the garage center of the specification if you want to get all of the car in the garage. Cpk Calculations In Excel Free Software' title='Cpk Calculations In Excel Free Software' />If the car is wider than the garage, it does not matter if you have it centered it will not fit. If the car is a lot smaller than the garage Six Sigma process, it doesnt matter if you park it exactly in the middle it will fit and you have plenty of room on either side. If you have a process that is in control and with little variation, you should be able to park the car easily within the garage and thus meet customer requirements. Cpk tells you the relationship between the size of the car, the size of the garage and how far away from the middle of the garage you parked the car. BenThe value itself can be thought of as the amount the process car can widen before hitting the nearest spec limit garage door edge. Cpk 12 means youve crunched nearest the door edge ouchCpk 1 means youre just touching the nearest edge. Cpk 2 means your width can grow 2 times before touching. Cpk 3 means your width can grow 3 times before touching Larry Seibel. Interpreting Pp, PpkProcess Performance Index basically tries to verify if the sample that you have generated from the process is capable to meet Customer CTQs requirements. It differs from Process Capability in that Process Performance only applies to a specific batch of material. Samples from the batch may need to be quite large to be representative of the variation in the batch. Process Performance is only used when process control cannot be evaluated. An example of this is for a short pre production run. Process Performance generally uses sample sigma in its calculation Process capability uses the process sigma value determined from either the Moving Range, Range or Sigma control charts. Praneet. Differences Between Cpk and PpkCpk is for short term, Ppk is for long term. Sundeep SinghPpk produces an index number like 1. Cpk references the variation to your specification limits. If you just want to know how much variation the process exhibits, a Ppk measurement is fine. If you want to know how that variation will affect the ability of your process to meet customer requirements CTQs, you should use Cpk. Michael WhaleyIt could be argued that the use of Ppk and Cpk with sufficient sample size are far more valid estimates of long and short term capability of processes since the 1. EoinCpk tells you what the process is CAPABLE of doing in future, assuming it remains in a state of statistical control. Ppk tells you how the process has performed in the past. You cannot use it predict the future, like with Cpk, because the process is not in a state of control. The values for Cpk and Ppk will converge to almost the same value when the process is in statistical control. F test. When out of control, the values will be distinctly different, perhaps by a very wide margin. Jim ParnellaCp 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. Download Excel 2010 Free' title='Download Excel 2010 Free' />Cpk Calculating Worksheet PR000665 4. Excel can save you time if you re planning on doing statistical data calculations. CPK is. Free Statistical Software. For both Ppk and Cpk the k stands for centralizing facteur  it assumes the index takes into consideration the fact that your data is maybe not centered and hence, your index shall be smaller. It is more realistic to use Pp and Ppk than Cp or Cpk as the process variation cannot be tempered with by inappropriate subgrouping. However, Cp and Cpk can be very useful in order to know if, under the best conditions, the process is capable of fitting into the specs or not. It basically gives you the best case scenario for the existing process. ChantalCp should always be greater than 2. Little Quacks here. For a good process under statistical control, Cpk should be greater than 1. Ranganadha KumarAs for PpkCpk, they mean one or the other and you will find people confusing the definitions and you WILL find books defining them versa and vice versa. Vector Frame there. You will have to ask the definition the person is using that you are talking to. Joe PeritoI just finished up a meeting with a vendor and we had a nice discussion of Cpk vs. Ppk. We had the definitions exactly reversed between us. Buy And Download ExcelThe outcome was to standardize on definitions and move forward from there. My suggestion to others is that each company have a procedure or document we do not, which has the definitions of Cpk and Ppk in it. This provides everyone a standard to refer to for WHEN we forget or get confused. John AdamoThe Six Sigma community standardized on definitions of Cp, Cpk, Pp, and Ppk from AIAG SPC manual page 8. You can get the manual for about 7. Gary. Calculating Cpk and PpkPp USL LSL6Std. Cpl Mean LSL3td. Cpu USL Mean3td. Cpk Min Cpl, Cpu Ranganadha KumarCpk is calculated using an estimate of the standard deviation calculated using R bard. Holes By Louis Sachar For. Ppk uses the usual form of the standard deviation ie the root of the variance or the square root of the sum of squares divided by n 1.