Processes Capabilities (Cp, Cpk) and Processes Show (Pp, Ppk) – What’s the Distinction?
In the Half dozen Sigma high quality strategy, process overall performance is advertised into business due to the fact good sigma top. The higher this new sigma top, the better the procedure is doing.
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
Whether your automobile is a lot smaller than new driveway (Six Sigma processes), it does not matter for folks who park they exactly in between; it does match and you have more than enough room on possibly 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 instance as well as C
“Consider a datingranking.net/tr/amateurmatch-inceleme/ 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 “Procedure Overall performance Index basically attempts to be certain that if the decide to try one you have got produced regarding processes is actually competent to fulfill Customers CTQs (requirements). They differs from Process Features where Techniques Show merely enforce so you can a specific batch off issue. Trials on the group could need to be some high to be user of one’s version regarding the batch. Techniques Overall performance is just used when process-control can not be evaluated. An example of it is to own a short pre-creation run. Process Overall performance basically uses take to sigma within the formula; Procedure capability spends the procedure sigma well worth determined of often the fresh Swinging Range, Diversity or Sigma handle maps.” Praneet