Processes Possibilities (Cp, Cpk) and you may Processes Abilities (Pp, Ppk) – What’s the Distinction?

Processes Possibilities (Cp, Cpk) and you may Processes Abilities (Pp, Ppk) – What’s the Distinction?

On Half a dozen Sigma high quality methods, processes show is actually stated to your team since the a good sigma peak. The greater brand new sigma peak, the higher the process is carrying out.

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.

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, Cpk “Cpk 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 Polhemus

“If 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.” Tommy

If for example the auto is a lot smaller than the fresh garage (Six Sigma processes), they doesnt count for those who park it just in-between; it does fit and you’ve got plenty of room towards the both front side

“Cpk 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.e., specification interval). pk will be lower, but Cp will be high. Cpk will be higher only when you r meeting the target consistently with minimum variation.” Ajit

This kind of situation together with C

“Consider 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. If the car is wider than the garage, it does not matter if you have it centered; it will not fit. 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.” Ben

“The value itself can be thought of as the amount the process (car) can widen before hitting the nearest spec limit (garage door edge).Cpk =1/2 means youve crunched nearest the door edge (ouch!)Cpk =1 means youre just touching the nearest edgeCpk =2 means your width can grow 2 times before touchingCpk =3 means your width can grow 3 times before touching” Larry Seibel

Interpreting Pp, Ppk “Techniques Overall performance Directory generally attempts to be certain that in case your test that you have made about process is competent to meet Customers CTQs (requirements). They is different from Techniques Capabilities where Techniques Results simply can be applied to a certain batch away from issue. Products regarding group might need to feel quite highest to help you become affiliate of adaptation on group. Process Efficiency is made use of whenever process-control can not be analyzed. A typical example of this can be having a short pre-design work at. Techniques Efficiency basically uses shot sigma within its calculation; Procedure abilities uses the procedure sigma worth computed out of sometimes the Swinging Range, Assortment otherwise Sigma control maps.” Praneet