Regarding Half dozen Sigma quality methodology, processes results try claimed towards providers due to the fact good sigma top. The better the fresh sigma level, the better the procedure is undertaking.
Another way to report process capability and process performance is through the statistical measurements of Cp, Cpk, Pp, and . This article will present definitions, interpretations and calculations for Cpk and though the use of forum quotations. Thanks to everyone below that helped contributed to this excellent reference.
A simple and easy straightforward sign from processes capabilities
Definitions Cp= 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. = 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
“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). 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.” Ajit
“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 the car is a lot smaller http://datingranking.net/college-dating/ 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.” 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 “Processes Results List essentially tries to verify in case the decide to try you to definitely you have generated on techniques is capable to see Buyers CTQs (requirements). They is different from Procedure Possibilities where Processes Results only applies so you’re able to a specific batch regarding procedure. Products in the batch may need to be a bit higher to feel user of version about group. Procedure Results is just utilized whenever process-control can not be examined. A good example of that is getting a primary pre-development run. Processes Show generally uses sample sigma in its calculation; Techniques functionality spends the process sigma well worth determined of either the latest Moving Range, Diversity or Sigma control maps.” Praneet